Publications

Is there an optimal basis to maximise optical information transfer?

We establish the concept of the density of the optical degrees of freedom that may be applied to any photonics based system. As a key example of this versatile approach we explore information transfer using optical communication. We demonstrate both experimentally, theoretically and numerically that the use of a basis set with fields containing optical vortices does not increase the telecommunication capacity of an optical system.

General information

State: E-pub ahead of print
Organisations: School of Physics and Astronomy
Authors: Chen, M., Dholakia, K., Mazilu, M.
Number of pages: 8
Publication date: 15 Mar 2016
Peer-reviewed: Yes
Early online date: 15 Mar 2016

Publication information

Journal: Scientific Reports
Volume: 6
Article number: 22821
ISSN (Print): 2045-2322
Original language: English
Electronic versions: 
 

Research output: Contribution to journalArticle

Measuring and structuring the spatial coherence length of organic light-emitting diodes

The spatial coherence of organic light-emitting diodes (OLEDs) is an important parameter that has gained little attention to date. Here we present a method for making quantitative measurements of the spatial coherence of OLEDs using a Young’s double-slit experiment. The usefulness of the method is demonstrated by making measurements on a range of OLEDs with different emitters (iridium and europium complexes) and architectures (bottom- and top-emitting) and the fringe visibility is further manipulated by gratings embedded in external diffractive optical elements. Based on the experiments and simulation of the results, we quantitatively determine the spatial coherence lengths of several OLEDs and find them to be a few micrometers. A 60% increase in the spatial coherence length was observed when using a narrow bandwidth emitter and a metal-coated grating.

General information

State: Published
Organisations: School of Physics and Astronomy, Condensed Matter Physics
Authors: Xie, G., Chen, M., Mazilu, M., Zhang, S., Bansal, A. K., Dholakia, K., Samuel, I. D. W.
Keywords:  (OLED, Double-slit experiment, Spatial coherence length, Diffractive optical element)
Pages: 82-90
Publication date: Jan 2016
Peer-reviewed: Yes

Publication information

Journal: Laser & Photonics Reviews
Volume: 10
Issue number: 1
ISSN (Print): 1863-8880
Original language: English

Bibliographical note

This work was supported by the Engineering and Physical Science Research Council (EPSRC) grants “Challenging the limits of photonics: structured light” EP/J01771X and “Ultra-parallel visible light communications” EP/K00042X. IDWS and KD also acknowledge Royal Society Wolfson Research Merit awards.

 

Research output: Contribution to journalArticle

Orbital angular momentum transfer to microparticles in vacuum: a new arena for quantum optomechanics

Optical vortex beams can be used to impart orbital angular momentum to microscopic particles. In vacuum, such beams offer a platform for new optomechanical studies of mesoscopic quantum systems including ground state degeneracy potentially showing collapse and revival phenomena, the Aharonov-Carmi thought experiment linking inertial and electro-magnetic vector potentials, or exploring quantum fictitious forces in rotating frames.
Here, we demonstrate the transfer of orbital angular momentum to an optically levitated particle in vacuum. The microparticle is placed within a Laguerre-Gaussian beam and orbits the annular beam profile with increasing angular velocity as the air drag coefficient is reduced. We are able to explore the particle dynamics as a function of the topological charge, L, of the levitating beam. The optomechanics of microparticles is determined by an interplay between the orbital angular momentum of the beam, the gravitational forces, the inertial forces and the radial trap stiffness.

General information

State: Submitted
Organisations: School of Physics and Astronomy
Authors: Mazilu, M., Arita, Y., Vettenburg, T., Aunon-Garcia, J. M., Wright, E. M., Dholakia, K.
Publication date: 2016
Peer-reviewed: Yes

Publication information

Journal: Nature Physics
ISSN (Print): 1745-2473
Original language: English
 

Research output: Contribution to journalArticle

1.2. 2015

Rotation of two trapped microparticles in vacuum: observation of optically mediated parametric resonances

We demonstrate trapping and rotation of two mesoscopic particles in vacuum using a spatial-light-modulator-based approach to trap more than one particle, induce controlled rotation of individual particles, and mediate interparticle separation. By trapping and rotating two vaterite particles, we observe intensity modulation of the scattered light at the sum and difference frequencies with respect to the individual rotation rates. This first demonstration of optical interference between two microparticles in vacuum leads to a platform to potentially explore optical binding and quantum friction effects.

General information

State: Published
Organisations: School of Physics and Astronomy, College of Optical Sciences, University of Arizona
Authors: Arita, Y., Mazilu, M., Vettenburg, T., Wright, E., Dholakia, K.
Keywords:  (Laser trapping, Optical tweezers, Optical manipulation, Harmonic generation and mixing)
Number of pages: 4
Pages: 4751-4754
Publication date: 15 Oct 2015
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 40
Issue number: 20
ISSN (Print): 0146-9592
Original language: English

Bibliographical note

Funding: Engineering and Physical Sciences Research Council (EPSRC) (EP/J01771X/1).

 

Research output: Contribution to journalArticle

Modulated Raman spectroscopy for enhanced cancer diagnosis at the cellular level

Raman spectroscopy is emerging as a promising and novel biophotonics tool for non-invasive, real-time diagnosis of tissue and cell abnormalities. However, the presence of a strong fluorescence background is a key issue that can detract from the use of Raman spectroscopy in routine clinical care. The review summarizes the state-of-the-art methods to remove the fluorescence background and explores recent achievements to address this issue obtained with modulated Raman spectroscopy. This innovative approach can be used to extract the Raman spectral component from the fluorescence background and improve the quality of the Raman signal. We describe the potential of modulated Raman spectroscopy as a rapid, inexpensive and accurate clinical tool to detect the presence of bladder cancer cells. Finally, in a broader context, we show how this approach can greatly enhance the sensitivity of integrated Raman spectroscopy and microfluidic systems, opening new prospects for portable higher throughput Raman cell sorting.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: De Luca, A. C., Dholakia, K., Mazilu, M.
Keywords:  (Raman spectroscopy, Cancer detection, Cell sensor, Fluorescence background, Highly fluorescent samples, Base-line correction, Difference spectroscopy, Biological samples, Multivariate-analysis, Bladder cancer, Light-source, Excitation, Rejection, Spectra)
Number of pages: 25
Pages: 13680-13704
Publication date: Jun 2015
Peer-reviewed: Yes

Publication information

Journal: Sensors
Volume: 15
Issue number: 6
ISSN (Print): 1424-8220
Original language: English
Electronic versions: 

Bibliographical note

We thank the UK and Engineering and Physical Sciences Research Council through grant number EP/J01771X/1.Date of Acceptance: 24/05/2015

Source: WOS
Source-ID: 000357869200082

Research output: Contribution to journalScientific review

The use of Wavelength Modulated Raman Spectroscopy in label-free identification of T lymphocyte subsets, Natural Killer cells and Dendritic cells

Determining the identity of cells of the immune system usually involves destructive fixation and chemical staining, or labeling with fluorescently labeled antibodies recognising specific cell surface markers. Completely label-free identification would be a significant advantage in conditions where untouched cells are a priority. We demonstrate here the use of Wavelength Modulated Raman Spectroscopy, to achieve label-free identification of purified, unfixed and untouched populations of major immune cell subsets isolated from healthy human donors. Using this technique we have been able to distinguish between CD4+ T lymphocytes, CD8+ T lymphocytes and CD56+ Natural Killer cells at specificities of up to 96%. Additionally, we have been able to distinguish between CD303+ plasmacytoid and CD1c+ myeloid dendritic cell subsets, the key initiator and regulatory cells of many immune responses. This demonstrates the ability to identify unperturbed cells of the immune system, and opens novel opportunities to analyse immunological systems and to develop fully label-free diagnostic technologies.

General information

State: Published
Organisations: School of Medicine, Biomedical Sciences Research Complex, School of Physics and Astronomy, INEB-Instituto de Engenharia Biomedica, Porto
Authors: Chen, M., McReynolds, N., Campbell, E. C., Mazilu, M., Barbosa, J., Dholakia, K., Powis, S. J.
Keywords:  (Raman spectroscopy, Dendritic cells, Natural killer cells, T Lymphocytes)
Publication date: 20 May 2015
Peer-reviewed: Yes

Publication information

Journal: PLoS One
Volume: 10
Issue number: 5
Article number: e0125158
ISSN (Print): 1932-6203
Original language: English
Electronic versions: 

Bibliographical note

This work was funded by a Cancer Research United Kingdom, Engineering and Physical Sciences Research Council (grant EP/J01771X/1), Medical Research Council and Department of Health England Imaging Programme (MC, MM KD), and by A European Union FAMOS project (FP7 ICT, 317744) to KD.

 

Research output: Contribution to journalArticle

Data Underpinning - Quantitative detection of pharmaceuticals using a combination of paper microfluidics and wavelength modulated Raman spectroscopy

Raman spectroscopy has proven to be an indispensable technique for the identification of various types of analytes due to the fingerprint vibration spectrum obtained. Paper microfluidics has also emerged as a low cost, easy to fabricate and portable approach for point of care testing. However, due to inherent background fluorescence, combining Raman spectroscopy with paper microfluidics is to date an unmet challenge in the absence of using surface enhanced mechanisms. We describe the first use of wavelength modulated Raman spectroscopy (WMRS) for analysis on a paper microfluidics platform. This study demonstrates the ability to suppress the background fluorescence of the paper using WMRS and the subsequent implementation of this technique for pharmaceutical analysis. The results of this study demonstrate that it is possible to discriminate between both paracetamol and ibuprofen, whilst, also being able to detect the presence of each analyte quantitatively at nanomolar concentrations.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Craig, D., Mazilu, M., Dholakia, K.
Publication date: 4 May 2015
Media of output: Online
 

Research output: Non-textual formData set/Database

Quantitative detection of pharmaceuticals using a combination of paper microfluidics and wavelength modulated Raman spectroscopy

Raman spectroscopy has proven to be an indispensable technique for the identification of various types of analytes due to the fingerprint vibration spectrum obtained. Paper microfluidics has also emerged as a low cost, easy to fabricate and portable approach for point of care testing. However, due to inherent background fluorescence, combining Raman spectroscopy with paper microfluidics is to date an unmet challenge in the absence of using surface enhanced mechanisms. We describe the first use of wavelength modulated Raman spectroscopy (WMRS) for analysis on a paper microfluidics platform. This study demonstrates the ability to suppress the background fluorescence of the paper using WMRS and the subsequent implementation of this technique for pharmaceutical analysis. The results of this study demonstrate that it is possible to discriminate between both paracetamol and ibuprofen, whilst, also being able to detect the presence of each analyte quantitatively at nanomolar concentrations.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Craig, D., Mazilu, M., Dholakia, K.
Number of pages: 10
Publication date: 4 May 2015
Peer-reviewed: Yes

Publication information

Journal: PLoS One
Volume: 10
Issue number: 5
Article number: e0123334
ISSN (Print): 1932-6203
Original language: English
Electronic versions: 
 

Research output: Contribution to journalArticle

Development of a graded index microlens based fiber optical trap and its characterization using principal component analysis

We demonstrate a miniaturized single beam fiber optical trapping probe based on a high numerical aperture graded index (GRIN) micro-objective lens. This enables optical trapping at a distance of 200μm from the probe tip. The fiber trapping probe is characterized experimentally using power spectral density analysis and an original approach based on principal component analysis for accurate particle tracking. Its use for biomedical microscopy is demonstrated through optically mediated immunological synapse formation.

General information

State: Published
Organisations: School of Physics and Astronomy, School of Medicine, Biomedical Sciences Research Complex, School of Biology, Institute of Behavioural and Neural Sciences
Authors: Nylk, J., Kristensen, M. V. G., Mazilu, M., Kubasik-Thayil, A., Mitchell, C. A., Campbell, E. C., Powis, S. J., Gunn-Moore, F. J., Dholakia, K.
Pages: 1512-1519
Publication date: 1 Apr 2015
Peer-reviewed: Yes
Early online date: 27 Mar 2015

Publication information

Journal: Biomedical Optics Express
Volume: 6
Issue number: 4
ISSN (Print): 2156-7085
Original language: English
Electronic versions: 

Bibliographical note

The authors thank the UK Engineering and Physical Sciences Research Council under grant EP/J01771X/1.

 

Research output: Contribution to journalArticle

Prospects for versatile phase manipulation in the TEM: beyond aberration correction

In this paper we explore the desirability of a transmission electron microscope in which the phase of the electron wave can be freely controlled. We discuss different existing methods to manipulate the phase of the electron wave and their limitations. We show how with the help of current techniques the electron wave can already be crafted into specific classes of waves each having their own peculiar properties. Assuming a versatile phase modulation device is feasible, we explore possible benefits and methods that could come into existence borrowing from light optics where the so-called spatial light modulators provide programmable phase plates for quite some time now. We demonstrate that a fully controllable phase plate building on Harald Rose's legacy in aberration correction and electron optics in general would open an exciting field of research and applications. Highlights:

General information

State: Published
Organisations: School of Physics and Astronomy, Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of St Andrews, EMAT, University of Antwerp
Authors: Guzzinati, G., Clark, L., Béché, A., Juchtmans, R., Van Boxem, R., Mazilu, M., Verbeeck, J.
Keywords:  (Vortex, Holography, Aberration correction, Electron optics, Airy waves)
Number of pages: 9
Pages: 85-93
Publication date: Apr 2015
Peer-reviewed: Yes
Early online date: 22 Oct 2014

Publication information

Journal: Ultramicroscopy
Volume: 151
ISSN (Print): 0304-3991
Original language: English

Bibliographical note

G.G., A.B., L.C. and J.V. acknowledge funding from the European Research Council under the Seventh Framework Program (FP7), ERC Starting Grant no. 278510 VORTEX. R.J. and R.v.B. acknowledge funding from FWO PhD Fellowship Grants (Aspirant Fonds Wetenschappelijk Onderzoek-Vlaanderen). J.V. also acknowledges funding from the European Union under the Seventh Framework Program under a contract for an Integrated Infrastructure Initiative. Reference no. 312483- ESTEEM2.

Source: Scopus
Source-ID: 84924769366

Research output: Contribution to journalArticle

Creating and probing of a perfect vortex in situ with an optically trapped particle

We experimentally create a 'perfect' vortex beam, which has a uniform ring profile and fixed radius. In contrast with other vortex fields, the intensity profile is independent of its topological charge. We then correct this field in situ using a single trapped particle as a probe. This results in a constant angular velocity for the particle regardless of its position on the beam circumference.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Chen, M., Mazilu, M., Arita, Y., Wright, E. M., Dholakia, K.
Keywords:  (Optical vortices, Optical manipulation, Optical tweezers, Modes, Light, Beam)
Number of pages: 4
Pages: 162-165
Publication date: Feb 2015
Peer-reviewed: Yes

Publication information

Journal: Optical Review
Volume: 22
Issue number: 1
ISSN (Print): 1340-6000
Original language: English
Electronic versions: 

Bibliographical note

The authors would like to thank the UK Engineering and Physical Sciences Research Council (EPSRC) for funding through grant EP/J01771X/1.

Source: WOS
Source-ID: 000353630200023

Research output: Contribution to journalArticle

Data Underpinning - Enhanced optical manipulation of cells using anti-reflection coated microparticles

We demonstrate the use of anti-reflection (AR) coated microparticles for the enhanced optical manipulation of cells. Specifically, we incubate both CHO-K1 and HL60 cell lines with AR coated titania microparticles and subsequently performed drag force measurements using optical trapping. Direct comparisons were performed between native, polystyrene microparticle and AR microparticle tagged cells. The optical trapping efficiency was recorded by measuring the Q value in a drag force experiment. CHO-K1 cells incubated with AR microparticles show an increase in the Q value of nearly 220% versus native cells. With the inclusion of AR microparticles, cell velocities exceeding 50um/s were recorded for only 33mW of laser trapping power. Cell viability was confirmed with fluorescent dyes and cells expressing a fluorescent ubiquitination-based cell cycle protein (FUCCI) which verified no disruption to the cell cycle in the presence of AR microparticles.

General information

State: Published
Organisations: School of Physics and Astronomy, School of Biology, Institute of Behavioural and Neural Sciences, Biomedical Sciences Research Complex
Authors: Craig, D., McDonald, A., Mazilu, M., Rendall, H. A., Gunn-Moore, F. J., Dholakia, K.
Publication date: 2015
 
Electronic versions: 
 

Research output: Non-textual formData set/Database

Data underpinning: Rotation of two trapped microparticles in vacuum: observation of optically mediated parametric resonances

We demonstrate trapping and rotation of two mesoscopic particles in vacuum using a spatial light modulator based approach to trap more than one particle, induce controlled rotation of individual particles and mediate inter-particle separation. By trapping and rotating two vaterite particles, we observe intensity modulation of the scattered light at the sum and difference frequencies with respect to the individual rotation rates. This first demonstration of optical interference between two microparticles in vacuum leads to a platform to potentially explore optical binding and quantum friction effects.

General information

State: Published
Organisations: School of Physics and Astronomy, Univ Arizona, University of Arizona, Coll Opt Sci
Authors: Arita, Y., Mazilu, M., Vettenburg, T., Wright, E. M., Dholakia, K.
Keywords:  (Laser trapping, Optical tweezers, optical manipulation, Harmonic generation and mixing)
Publication date: 2015
 
Electronic versions: 
 

Research output: Non-textual formData set/Database

EigenOptics v1.00

Matlab scripts to calculate optical forces using the optical eigenmode approach. Used in several publications.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Mazilu, M.
Publication date: 2015
 
Electronic versions: 
 

Research output: Non-textual formData set/Database

Enhanced optical manipulation of cells using anti-reflection coated microparticles

We demonstrate the use of anti-reflection (AR) coated microparticles for the enhanced optical manipulation of cells. Specifically, we incubate both CHO-K1 and HL60 cell lines with AR coated titania microparticles and subsequently performed drag force measurements using optical trapping. Direct comparisons were performed between native, polystyrene microparticle and AR microparticle tagged cells. The optical trapping efficiency was recorded by measuring the Q value in a drag force experiment. CHO-K1 cells incubated with AR microparticles show an increase in the Q value of nearly 220% versus native cells. With the inclusion of AR microparticles, cell velocities exceeding 50um/s were recorded for only 33mW of laser trapping power. Cell viability was confirmed with fluorescent dyes and cells expressing a fluorescent ubiquitination-based cell cycle protein (FUCCI) which verified no disruption to the cell cycle in the presence of AR microparticles.

General information

State: Published
Organisations: School of Physics and Astronomy, School of Biology, Institute of Behavioural and Neural Sciences, Biomedical Sciences Research Complex
Authors: Craig, D., McDonald, A., Mazilu, M., Rendall, H. A., Gunn-Moore, F. J., Dholakia, K.
Keywords:  (Optical trapping, Dielectric tagging, Anti-reflection, Microparticles, Biophotonics, Cell viability)
Pages: 1403-1409
Publication date: 2015
Peer-reviewed: Yes
Early online date: 11 Sep 2015

Publication information

Journal: ACS Photonics
Volume: 2
Issue number: 10
Original language: English

Bibliographical note

The authors thank the UK Engineering and Physical Sciences Research Council under grants EP/J01771X/1 and EP/M000869/1, the University of St Andrews, the BRAINS 600th anniversary appeal and Dr. Killick for funding.

 

Research output: Contribution to journalArticle

1.3. 2014

Biologically enabled sub-diffractive focusing

Evolution shows that photonic structures are a constituent part of many animals and flora. These elements produce structural color and are useful in predator-prey interactions between animals and in the exploitation of light for photosynthetic organisms. In particular, diatoms have evolved patterned hydrated silica external valves able to confine light with extraordinary efficiency. Their evolution was probably guided by the necessity to survive in harsh conditions of sunlight deprivation. Here, we exploit such diatom valves, in conjunction with structured illumination, to realize a biological super-resolving lens to achieve sub-diffractive focusing in the far field. More precisely, we consider a single diatom valve of Arachnoidiscus genus which shows symmetries and fine features. By characterizing and using the transmission properties of this valve using the optical eigenmode technique, we are able to confine light to a tiny spot with unprecedented precision in terms of resolution limit ratio, corresponding in this case to 0.21 λ/NA.

General information

State: Published
Organisations: School of Physics and Astronomy, CNR, Consiglio Nazionale delle Ricerche (CNR), Inst Microelect & Microsyst, Dept Naples, Univ Naples 2, Seconda Universita degli Studi di Napoli, Dept Environm Biol & Pharmaceut Sci & Technol, Univ Naples 2, Seconda Universita degli Studi di Napoli, Dept Architecture & Ind Design Luigi Vanvitelli
Authors: De Tommasi, E., De Luca, A. C., Lavanga, L., Dardano, P., De Stefano, M., De Stefano, L., Langella, C., Rendina, I., Dholakia, K., Mazilu, M.
Keywords:  (Optical eigenmodes, Diatom frustules, Light, Nanostructures)
Number of pages: 14
Pages: 27214-27227
Publication date: 3 Nov 2014
Peer-reviewed: Yes
Early online date: 27 Oct 2014

Publication information

Journal: Optics Express
Volume: 22
Issue number: 22
ISSN (Print): 1094-4087
Original language: English

Bibliographical note

EDT, LL, MDS, CL, LDS are supported by a FIR project RBFR12WAPY. ACDL is supported by an AIRC Start-up Grant 11454 and a FIR project RBFR12WAPY. KD thanks the UK EPSRC for funding.

Source: WOS
Source-ID: 000344004900076

Research output: Contribution to journalArticle

Nonredundant Raman imaging using optical eigenmodes

Various forms of imaging schemes have emerged over the last decade that are based on correlating variations in incident illuminating light fields to the outputs of single “bucket” detectors. However, to date, the role of the orthogonality of the illumination fields has largely been overlooked, and, furthermore, the field has not progressed beyond bright field imaging. By exploiting the concept of orthogonal illuminating fields, we demonstrate the application of optical eigenmodes (OEis) to wide-field, scan-free spontaneous Raman imaging, which is notoriously slow in wide-field mode. The OEi approach enables a form of indirect imaging that exploits both phase and amplitude in image reconstruction. The use of orthogonality enables us to nonredundantly illuminate the sample and, in particular, use a subset of illuminating modes to obtain the majority of information from the sample, thus minimizing any photobleaching or damage of the sample. The crucial incorporation of phase, in addition to amplitude, in the imaging process significantly reduces background noise and results in an improved signal-to-noise ratio for the image while reducing the number of illuminations. As an example we can reconstruct images of a surface-enhanced Raman spectroscopy sample with approximately an order of magnitude fewer acquisitions. This generic approach may readily be applied to other imaging modalities such as fluorescence microscopy or nonlinear vibrational microscopy.

General information

State: Published
Organisations: School of Physics and Astronomy, School of Medicine
Authors: Kosmeier, S., Zolotovskaya, S., De Luca, A. C., Riches, A. C., Herrington, C. S., Dholakia, K., Mazilu, M.
Number of pages: 7
Pages: 257-263
Publication date: 17 Oct 2014
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 1
Issue number: 4
Original language: English
Electronic versions: 

Bibliographical note

We thank funding from the UK Engineering and Physical Sciences Research Council namely grant EP/J01771X/1 and EU FP7 grant FAMOS.

Source: RIS
Source-ID: urn:9B688D4056BA182C4D51797260823475

Research output: Contribution to journalArticle

Optical trapping with a perfect vortex beam

Vortex beams with different topological charge usually have different profiles and radii of peak intensity. This introduces a degree of complexity the fair study of the nature of optical OAM (orbital angular momentum). To avoid this, we introduced a new approach by creating a perfect vortex beam using an annular illuminating beam with a fixed intensity profile on an SLM that imposes a chosen topological charge. The radial intensity profile of such an experimentally created perfect vortex beam is independent to any given integer value of its topological charge. The well-defined OAM density in such a perfect vortex beam is probed by trapping microscope particles. The rotation rate of a trapped necklace of particles is measured for both integer and non-integer topological charge. Experimental results agree with the theoretical prediction. With the flexibility of our approach, local OAM density can be corrected in situ to overcome the problem of trapping the particle in the intensity hotspots. The correction of local OAM density in the perfect vortex beam therefore enables a single trapped particle to move along the vortex ring at a constant angular velocity that is independent of the azimuthal position. Due to its particular nature, the perfect vortex beam may be applied to other studies in optical trapping of particles, atoms or quantum gases.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Chen, M., Mazilu, M., Arita, Y., Wright, E. M., Dholakia, K.
Keywords:  (Optical Trapping, perfect vortex, Orbital Angular Momentum (OAM), Orbital angular-momentum, Modes, Light)
Number of pages: 5
Publication date: 16 Sep 2014

Host publication information

Title of host publication: Optical Trapping and Optical Micromanipulation XI
Place of publication: Bellingham
Publisher: SPIE-The International Society for Optical Engineering
Editors: Dholakia, K., Spalding, G.

Publication series

Name: Proceedings of SPIE
Publisher: SPIE-INT SOC OPTICAL ENGINEERING
Volume: 9164
ISSN (Print): 0277-786X
Electronic versions: 

Bibliographical note

The authors would like to thank the UK Engineering and Physical Sciences Research Council (EPSRC) for funding.

Source: WOS
Source-ID: 000349300600011

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Generation of attenuation-compensating Airy beams

We present an attenuation-corrected "nondiffracting" Airy beam. The correction factor can be adjusted to deliver a beam that exhibits an adjustable exponential intensity increase or decrease over a finite distance. A digital micro-mirror device that shapes both amplitude and phase is used to experimentally verify the propagation of these beams through air and partially absorbing media. (C) 2014 Optical Society of America

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Preciado, M. A., Dholakia, K., Mazilu, M.
Keywords:  (Digital micromirror device, Wave-packets)
Number of pages: 4
Pages: 4950-4953
Publication date: 15 Aug 2014
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 39
Issue number: 16
ISSN (Print): 0146-9592
Original language: English
Electronic versions: 
  • 212492. Embargo ended: 15/08/15

Bibliographical note

This research was supported by the UK Engineering and Physical Sciences Council
Programme Grant EP/J01771X/1 and Royal Society research grant RG130854.

Source: WOS
Source-ID: 000341099400081

Research output: Contribution to journalArticle

Reproducible surface-enhanced Raman quantification of biomarkers in multicomponent mixtures

Direct and quantitative detection of unlabeled glycerophosphoinositol (GroPIns), an abundant cytosolic phosphoinositide derivative, would allow rapid evaluation of several malignant cell transformations. Here we report label-free analysis of GroPIns via surface-enhanced Raman spectroscopy (SERS) with a sensitivity of 200 nM, well below its apparent concentration in cells. Crucially, our SERS substrates, based on lithographically defined gold nanofeatures, can be used to predict accurately the GroPIns concentration even in multicomponent mixtures, avoiding the preliminary separation of individual compounds. Our results represent a critical step toward the creation of SERS-based biosensor for rapid, label-free, and reproducible detection of specific molecules, overcoming limits of current experimental methods.

General information

State: Published
Organisations: School of Physics and Astronomy, CNR, Consiglio Nazionale delle Ricerche (CNR), Inst Prot Biochem
Authors: De Luca, A. C., Reader-Harris, P., Mazilu, M., Mariggio, S., Corda, D., Di Falco, A.
Keywords:  (SERS, Biosensor, Glycerophosphoinositol, Nanofabrication, Label-free detection, Tandem mass-spectrometry, Spectroscopy, Scattering, Substrate, Silver, Glycerophosphoinositols, Nanosensors, Spectra, Arrays)
Number of pages: 9
Pages: 2575-2583
Publication date: Mar 2014
Peer-reviewed: Yes
Early online date: 13 Feb 2014

Publication information

Journal: ACS Nano
Volume: 8
Issue number: 3
ISSN (Print): 1936-0851
Original language: English
Electronic versions: 

Bibliographical note

A.C.D.L. is supported by an AIRC Start-up Grant 11454 and a FIR project RBFR12WAPY. A.D.F. is supported by an EPSRC Career Acceleration Fellowship (EP/I004602/1). D.C. is supported by an AIRC Grant IG10341 and the projects PON01-00117 and PON01-00862. S.M. is supported by a PRIN project 2012CK5RPF_05.

Source: WOS
Source-ID: 000333539400071

Research output: Contribution to journalArticle

Density of optical degrees of freedom: intensity, linear and angular momentum

For any optical system, optical eigenmodes describe solutions of Maxwells equations that are orthogonal to each other. In their simplest free space form, these modes correspond, for example, to Bessel, Laguerre-Gaussian or Hermite-Gaussian beams. However, the orthogonality property is not limited to the intensity of the optical field but more generally the optical eigenmode decomposition can be applied to the linear and angular momentum arising from complex coherent beams. These modes can be seen as describing the independent degrees of freedom of the optical system and are characterized by the mode, their density and coupling efficiency. It is interesting to study the effect of different optical systems on the density of the optical degrees of freedom propagating through them. Here, we look at systems containing different elements such as: dielectric, meta-material and random lenses. Using the optical eigenmode decomposition, we determine their density in these different cases and discuss the origin of the variations observed. Further, we study the overall number of optical degrees of freedom accessible including linear and angular momentum of optical beams.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Mazilu, M.
Keywords:  (Optical eigenmodes, Structured illumination, Optical degrees of freedom)
Number of pages: 6
Publication date: 25 Feb 2014

Host publication information

Title of host publication: Complex Light and Optical Forces VIII
Volume: 8999
Place of publication: Bellingham
Publisher: SPIE-The International Society for Optical Engineering
Editors: Andrews, D., Galvez, E., Gluckstad, J.

Publication series

Name: Proceedings of SPIE
Publisher: SPIE-The International Society for Optical Engineering
Volume: 8999
ISSN (Print): 0277-786X
Electronic versions: 
Source: WOS
Source-ID: 000338075400014

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Random super-prism wavelength meter

The speckle pattern arising from a thin random, disordered scatterer may be used to detect the transversal mode of an incident beam. On the other hand, speckle patterns originating from meter-long multimode fibers can be used to detect different wavelengths. Combining these approaches, we develop a method that uses a thin random scattering medium to measure the wavelength of a near-infrared laser beam with picometer resolution. The method is based on the application of principal component analysis, which is used for pattern recognition and is applied here to the case of speckle pattern categorization.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Mazilu, M., Vettenburg, T., Di Falco, A., Dholakia, K.
Keywords:  (Spectrometer, Resolution, Media, Fiber)
Number of pages: 4
Pages: 96-99
Publication date: 1 Jan 2014
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 39
Issue number: 1
ISSN (Print): 0146-9592
Original language: English
Electronic versions: 

Bibliographical note

The authors acknowledge the UK Engineering and Physical Sciences Research Council for funding (EP/J004200/1). ADF is a EPSRC fellow (EP/I004602/1). Kishan Dholakia is a Royal Society-Wolfson Merit Award Holder.

Source: WOS
Source-ID: 000329033400027

Research output: Contribution to journalArticle

Biomolecular sensing for cancer diagnostics using highly reproducible SERS substrates

We developed a SERS biosensor based on gold fishnets fabricated by using e-beam lithography. This device is used for glycerophosphoinositol (GroPIns) molecule sensing. GroPIns is an abundant component of cell cytosol and high GroPIns levels have been reported in several tumour cells. We demonstrate that our SERS sensor is able to accurately and quantitatively determine the concentration of GroPIns. These results indicate that SERS may provide a novel platform technology to identify GroPIns profiles in disease pathogenesis.

General information

State: Published
Organisations: School of Physics and Astronomy, CNR, Consiglio Nazionale delle Ricerche (CNR), Inst Prot Biochem
Authors: De Luca, A. C., Reader-Harris, P., Mazilu, M., Manago, S., Mariggio, S., Corda, D., Di Falco, A.
Keywords:  (SERS, Cancer diagnostic, Glycerophosphoinositol, Biosensor, Reproducibility, SURFACE-ENHANCED RAMAN, SPECTROSCOPY, SCATTERING, SILVER)
Number of pages: 7
Publication date: 2014

Host publication information

Title of host publication: PLASMONICS IN BIOLOGY AND MEDICINE XI
Publisher: SPIE-The International Society for Optical Engineering
Editors: VoDinh, T., Lakowicz

Publication series

Name: Proceedings of SPIE
Publisher: SPIE-INT SOC OPTICAL ENGINEERING
Volume: 8957
ISSN (Print): 0277-786X
Source: WOS
Source-ID: 000335492800005

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1.4. 2013

Effect of the radial and azimuthal mode indices of a partially coherent vortex field upon a spatial correlation singularity

The existence of a spatial correlation singularity or a ring dislocation in the spatial coherence function when a vortex is present has been demonstrated recently. Here, we investigate how the spatial correlation singularity is affected by both the radial and azimuthal mode indices (p, l) in a partially coherent light field. Theoretically, we find that the spatial correlation singularity may exist even in a non-vortex beam (l = 0) due to the radial index. Numerical simulations show the number of ring dislocations in the far-field cross correlation function is equal to 2p + vertical bar l vertical bar for the low coherence cases. This is confirmed by our experimental results. This phenomenon may occur in any partially coherent vortex wave.

General information

State: Published
Organisations: School of Physics and Astronomy, Univ Elect Sci & Technol China, University of Electronic Science & Technology - China, Sch Aeronaut & Astronaut, Univ St Andrews, University of St Andrews, Dept Phys & Astron, SUPA, Univ Elect Sci & Technol China, University of Electronic Science & Technology - China, Sch Phys Elect
Authors: Yang, Y., Chen, M., Mazilu, M., Mourka, A., Liu, Y., Dholakia, K.
Keywords:  (Orbital angular-momentum, Light, Vortices, Beams)
Number of pages: 9
Publication date: 26 Nov 2013
Peer-reviewed: Yes

Publication information

Journal: New Journal of Physics
Volume: 15
Article number: 113053
ISSN (Print): 1367-2630
Original language: English
Electronic versions: 

Bibliographical note

Funding: UK Engineering and Physical Sciences Research Council for funding. YY
acknowledges support by the National Natural Science Foundation of China under grant numbers 61205122, 60908034 and 61107037, the Fundamental Research Funds for the Central Universities under grant no. ZYGX2010J112, and Doctoral Fund of Ministry of Education of China under grant no. 20090185120016. KD is a Royal Society-Wolfson Merit Award Holder.

Source: WOS
Source-ID: 000327550700008

Research output: Contribution to journalArticle

Laser-induced rotation and cooling of a trapped microgyroscope in vacuum

Quantum state preparation of mesoscopic objects is a powerful playground for the elucidation of many physical principles. The field of cavity optomechanics aims to create these states through laser cooling and by minimizing state decoherence. Here we demonstrate simultaneous optical trapping and rotation of a birefringent microparticle in vacuum using a circularly polarized trapping laser beam—a microgyroscope. We show stable rotation rates up to 5 MHz. Coupling between the rotational and translational degrees of freedom of the trapped microgyroscope leads to the observation of positional stabilization in effect cooling the particle to 40 K. We attribute this cooling to the interaction between the gyroscopic directional stabilization and the optical trapping field.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Arita, Y., Mazilu, M., Dholakia, K.
Keywords:  (Optical physics)
Publication date: 28 Aug 2013
Peer-reviewed: Yes

Publication information

Journal: Nature Communications
Volume: 4
Article number: 2374
ISSN (Print): 2041-1723
Original language: English

Bibliographical note

This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC grant numbers: EP/J01771X/1 and EP/G061688/1)

 

Research output: Contribution to journalArticle

Exploiting lens aberrations to create electron-vortex beams

A model for a new electron vortex beam production method is proposed and experimentally demonstrated. The technique calls on the controlled manipulation of the degrees of freedom of the lens aberrations to achieve a helical phase front. These degrees of freedom are accessible by using the corrector lenses of a transmission electron microscope. The vortex beam is produced through a particular alignment of these lenses into a specifically designed astigmatic state and applying an annular aperture in the condensor plane. Experimental results are found to be in good agreement with simulations.

General information

State: Published
Organisations: School of Physics and Astronomy, EMAT, University of Antwerp, Triebenberglabor, University of Dresden
Authors: Clark, L., Béché, A., Guzzinati, G., Lubk, A., Mazilu, M., Van Boxem, R., Verbeeck, J.
Number of pages: 5
Publication date: Aug 2013
Peer-reviewed: Yes

Publication information

Journal: Physical Review Letters
Volume: 111
Issue number: 6
Article number:  064801
ISSN (Print): 0031-9007
Original language: English
 

Research output: Contribution to journalArticle

Optimisation of wavelength modulated Raman spectroscopy: towards high throughput cell screening

In the field of biomedicine, Raman spectroscopy is a powerful technique to discriminate between normal and cancerous cells. However the strong background signal from the sample and the instrumentation affects the efficiency of this discrimination technique. Wavelength Modulated Raman spectroscopy (WMRS) may suppress the background from the Raman spectra. In this study we demonstrate a systematic approach for optimizing the various parameters of WMRS to achieve a reduction in the acquisition time for potential applications such as higher throughput cell screening. The Signal to Noise Ratio (SNR) of the Raman bands depends on the modulation amplitude, time constant and total acquisition time. It was observed that the sampling rate does not influence the signal to noise ratio of the Raman bands if three or more wavelengths are sampled. With these optimised WMRS parameters, we increased the throughput in the binary classification of normal human urothelial cells and bladder cancer cells by reducing the total acquisition time to 6 s which is significantly lower in comparison to previous acquisition times required for the discrimination between similar cell types.

General information

State: Published
Organisations: School of Physics and Astronomy, School of Medicine, Univ St Andrews, University of St Andrews, Sch Phys & Astron, SUPA
Authors: Praveen, B. B., Mazilu, M., Marchington, R. F., Herrington, C. S., Riches, A., Dholakia, K.
Keywords:  (Absorption spectroscopy, Wavelength Modulated Raman spectroscopy (WMRS), Cell screening, Signal to Noise Ratio (SNR), Urothelial cells , Bladder cancer cells)
Number of pages: 5
Publication date: 25 Jun 2013
Peer-reviewed: Yes

Publication information

Journal: PLoS One
Volume: 8
Issue number: 6
Article number: e67211
ISSN (Print): 1932-6203
Original language: English
Electronic versions: 
Source: WOS
Source-ID: 000321223000091

Research output: Contribution to journalArticle

Enhanced Cell Transfection using sub-wavelength focused optical eigenmode beams

We show that superoscillating light fields, created using the method of optical eigenmodes, enable more efficient multiphoton-mediated cell transfection. Chinese hamster ovary cells are transfected with a plasmid and exhibit expression of DsRed-Mito in the mitochondria. We demonstrate an efficiency improvement of 35% compared to the diffraction-limited spot. This opens up new vistas for nanoscale localized cell transfection. © 2013 Chinese Laser Press

General information

State: Published
Organisations: School of Biology, Institute of Behavioural and Neural Sciences, Biomedical Sciences Research Complex, School of Physics and Astronomy
Authors: Tsampoula, X., Mazilu, M., Vettenburg, T., Gunn-Moore, F. J., Dholakia, K.
Number of pages: 5
Pages: 42-46
Publication date: 11 Jun 2013
Peer-reviewed: Yes

Publication information

Journal: Photonics Research
Volume: 1
Issue number: 1
Original language: English
 

Research output: Contribution to journalArticle

Coherent control of plasmonic nanoantennas using optical eigenmodes

The last decade has seen subwavelength focusing of the electromagnetic field in the proximity of nanoplasmonic structures with various designs. However, a shared issue is the spatial confinement of the field, which is mostly inflexible and limited to fixed locations determined by the geometry of the nanostructures, which hampers many applications. Here, we coherently address numerically and experimentally single and multiple plasmonic nanostructures chosen from a given array, resorting to the principle of optical eigenmodes. By decomposing the light field into optical eigenmodes, specifically tailored to the nanostructure, we create a subwavelength, selective and dynamic control of the incident light. The coherent control of plasmonic nanoantennas using this approach shows an almost zero crosstalk. This approach is applicable even in the presence of large transmission aberrations, such as present in holographic diffusers and multimode fibres. The method presents a paradigm shift for the addressing of plasmonic nanostructures by light.

General information

State: Published
Organisations: School of Physics and Astronomy, Microphotonics and Photonic Crystals Group
Authors: Kosmeier, S., De Luca, A. C., Zolotovskaya, S., Di Falco, A., Dholakia, K., Mazilu, M.
Publication date: 9 May 2013
Peer-reviewed: Yes

Publication information

Journal: Scientific Reports
Volume: 3
Article number: 1808
ISSN (Print): 2045-2322
Original language: English
Electronic versions: 
 

Research output: Contribution to journalArticle

Collision of propagating vortices embedded within Airy beams

We present the engineered collision of two curvilinear propagating optical vortices each embedded in the main lobe of an Airy beam. Two cases are analyzed: the same and opposite unitary topological vortex charge. We observed experimentally that in the first case the main vortices repel each other and remain separated after the collision. In contrast, in the second case an annihilation of the main vortices occurs. Our experimental observations are reinforced by numerical simulations showing that the conservation of topological charge dictates the vortex dynamics.

General information

State: Published
Organisations: School of Physics and Astronomy, Inst Nacl Astrofis Opt & Electr
Authors: Rosales-Guzman, C., Mazilu, M., Baumgartl, J., Rodriguez-Fajardo, V., Ramos-Garcia, R., Dholakia, K.
Keywords:  (Optical vortices, Airy beams, Wave-front, Dislocations, Singularities, Annihilation, Field)
Number of pages: 6
Publication date: Apr 2013
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics
Volume: 15
Issue number: 4
Article number: 044001
ISSN (Print): 2040-8978
Original language: English
Source: WOS
Source-ID: 000317484800002

Research output: Contribution to journalArticle

Modal characterization using principal component analysis: application to Bessel, higher-order Gaussian beams and their superposition

The modal characterization of various families of beams is a topic of current interest. We recently reported a new method for the simultaneous determination of both the azimuthal and radial mode indices for light fields possessing orbital angular momentum. The method is based upon probing the far-field diffraction pattern from a random aperture and using the recorded data as a 'training set'. We then transform the observed data into uncorrelated variables using the principal component analysis (PCA) algorithm. Here, we show the generic nature of this approach for the simultaneous determination of the modal parameters of Hermite-Gaussian and Bessel beams. This reinforces the widespread applicability of this method for applications including information processing, spectroscopy and manipulation. Additionally, preliminary results demonstrate reliable decomposition of superpositions of Laguerre-Gaussians, yielding the intensities and relative phases of each constituent mode. Thus, this approach represents a powerful method for characterizing the optical multi-dimensional Hilbert space.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Mourka, A., Mazilu, M., Wright, E. M., Dholakia, K.
Keywords:  (Orbital angular-momentum, Light-beams, Diffraction, Modes, Decomposition, Information, Intensity, Systems , Planes, Phase)
Number of pages: 8
Publication date: 12 Mar 2013
Peer-reviewed: Yes

Publication information

Journal: Scientific Reports
Volume: 3
Article number: 1422
ISSN (Print): 2045-2322
Original language: English
Electronic versions: 

Bibliographical note

This work was funded by the EPSRC.

Source: WOS
Source-ID: 000315938000003

Research output: Contribution to journalArticle

1.5. 2012

Measuring the orbital angular momentum of partially coherent optical vortices through singularities in their cross-spectral density functions

By analysis of the far-field cross-correlation function (CCF) of partially coherent optical beams, we demonstrate an implicit rule that the number of ring dislocations (dark zones) of the far-field CCF is equal to the original topological charge of an optical vortex rendered partially coherent. This novel link between an optical vortex and its correlation singularity may offer an efficient method for measuring the orbital angular momentum of partially coherent optical vortices in fields such as astrophysics and astronomy, as well as atmospheric laser communication.

General information

State: Published
Organisations: School of Physics and Astronomy, Univ St Andrews, University of St Andrews, Sch Phys & Astron, SUPA, Univ Elect Sci & Technol China, University of Electronic Science & Technology - China, Inst Aeronaut & Astronaut
Authors: Yang, Y., Mazilu, M., Dholakia, K.
Keywords:  (Space, Vortex beam, Triangular aperture, Topological charge)
Number of pages: 3
Pages: 4949-4951
Publication date: 1 Dec 2012
Peer-reviewed: Yes

Publication information

Journal: Optics Letters
Volume: 37
Issue number: 23
ISSN (Print): 0146-9592
Original language: English
Electronic versions: 

Bibliographical note

This work is supported by UK EPSRC

Source: WOS
Source-ID: 000311943900048

Research output: Contribution to journalArticle

An interacting dipole model to explore broadband transverse optical binding

The demonstration of optical binding of micro-particles placed in intense optical fields has resulted in unique and exciting prospects for studying new forms of condensed matter. The ability to tailor optical fields in the spatial and temporal domains elicits the possibility of creating novel condensed matter with the structure controlled by tailoring the optical field. Here, we theoretically calculate the transverse optical binding forces for nanoparticles within monochromatic and broadband optical fields. We demonstrate the decrease in amplitude of the optical binding forces for broadband fields as a function of inter-particle separation and attribute the effect to the averaging effect of spectrally dependent optical forces. We also examine multiple particle optically bound systems and use the interacting dipole method to find self-organized positions for six and ten particles illuminated by a monochromatic plane wave.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Mazilu, M., Rudhall, A., Wright, E. M., Dholakia, K.
Keywords:  (Radiation forces, Particles, Approximation, Manipulation, Grains, Lasers, Light , Array)
Number of pages: 6
Publication date: 21 Nov 2012
Peer-reviewed: Yes

Publication information

Journal: Journal of Physics: Condensed Matter
Volume: 24
Issue number: 46
Article number: 464117
ISSN (Print): 0953-8984
Original language: English

Bibliographical note

Funding: UK Engineering and Physical Sciences Research.

Source: WOS
Source-ID: 000310836300018

Research output: Contribution to journalArticle

Auto-focusing and self-healing of Pearcey beams

We present a new solution of the paraxial equation based on the Pearcey function, which is related to the Airy function and describes diffraction about a cusp caustic. The Pearcey beam displays properties similar not only to Airy beams but also Gaussian and Bessel beams. These properties include an inherent auto-focusing effect, as well as form-invariance on propagation and self-healing. We describe the theory of propagating Pearcey beams and present experimental verification of their auto-focusing and self-healing behaviour. (C) 2012 Optical Society of America

General information

State: Published
Organisations: School of Physics and Astronomy, Univ Bristol, University of Bristol, HH Wills Phys Lab
Authors: Ring, J. D., Lindberg, J., Mourka, A., Mazilu, M., Dholakia, K., Dennis, M. R.
Keywords:  (Abruptly autofocusing waves, Bessel-gauss beams, Airy beams, Property, Scalar)
Number of pages: 12
Pages: 18955-18966
Publication date: 13 Aug 2012
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 20
Issue number: 17
ISSN (Print): 1094-4087
Original language: English

Bibliographical note

EPSRC. KD is a Royal Society Wolfson Merit Award holder and MRD is a Royal Society University Research Fellow.

Source: WOS
Source-ID: 000307873600045

Research output: Contribution to journalArticle

Fluorescence suppression using wavelength modulated Raman spectroscopy in fiber-probe-based tissue analysis

In the field of biomedical optics, Raman spectroscopy is a powerful tool for probing the chemical composition of biological samples. In particular, fiber Raman probes play a crucial role for in vivo and ex vivo tissue analysis. However, the high-fluorescence background typically contributed by the auto fluorescence from both a tissue sample and the fiber-probe interferes strongly with the relatively weak Raman signal. Here we demonstrate the implementation of wavelength-modulated Raman spectroscopy (WMRS) to suppress the fluorescence background while analyzing tissues using fiber Raman probes. We have observed a significant signal-to-noise ratio enhancement in the Raman bands of bone tissue, which have a relatively high fluorescence background. Implementation of WMRS in fiber-probe-based bone tissue study yielded usable Raman spectra in a relatively short acquisition time (∼30  s), notably without any special sample preparation stage. Finally, we have validated its capability to suppress fluorescence on other tissue samples such as adipose tissue derived from four different species.

General information

State: Published
Organisations: School of Physics and Astronomy, School of Medicine
Authors: Balagopal, B., Ashok, P. C., Mazilu, M., Riches, A. C., Herrington, C. S., Dholakia, K.
Keywords:  (Biophotonics, Bone tissue studies, Raman probe, Raman spectroscopy, Tissues)
Number of pages: 6
Publication date: 9 Jul 2012
Peer-reviewed: Yes

Publication information

Journal: Journal of Biomedical Optics
Volume: 17
Issue number: 7
Article number: 077006
ISSN (Print): 1083-3668
Original language: English

Bibliographical note

The work was funded by CR-UK/EPSRC/MRC/DoH (England) imaging programme.

 

Research output: Contribution to journalArticle

Simultaneous determination of the constituent azimuthal and radial mode indices for light fields possessing orbital angular momentum

A wide array of diffractive structures such as arrays of pinholes, triangular apertures, slits, and holograms have all recently been used to measure the azimuthal index of individual Laguerre-Gaussian beams. Here, we demonstrate a powerful approach to simultaneously measure both the radial and azimuthal indices of pure Laguerre-Gaussian light fields using the method of principal component analysis. We find that the shape of the diffracting element used to measure the mode indices is in fact of little importance and the crucial step is training any diffracting optical system and transforming the observed pattern into uncorrelated variables. The method is generic and may be extended to other families of light fields such as Bessel or Hermite-Gaussian beams.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Mazilu, M., Mourka, A., Vettenburg, T., Wright, E. M., Dholakia, K.
Keywords:  (Laguerre-Gaussian beams, Azimuthal index , Principal component analysis, Optical system , Hermite-Gaussian beams)
Number of pages: 4
Publication date: 4 Jun 2012
Peer-reviewed: Yes

Publication information

Journal: Applied Physics Letters
Volume: 100
Issue number: 23
Article number: 231115
ISSN (Print): 0003-6951
Original language: English
Electronic versions: 

Bibliographical note

This work received Engineering and Physical Sciences Research Council funding.

Source: WOS
Source-ID: 000305089900015

Research output: Contribution to journalArticle

Algorithm-based continuous pulse duration tuning and performance control of a mode-locked laser diode

A control algorithm is presented that addresses the stability issues inherent to the operation of monolithic mode-locked laser diodes. It enables a continuous pulse duration tuning without any onset of Q-switching instabilities. A demonstration of the algorithm performance is presented for two radically different laser diode geometries and continuous pulse duration tuning between 0.5 ps to 2.2 ps and 1.2 ps to 10.2 ps is achieved. With practical applications in mind, this algorithm also facilitates control over performance parameters such as output power and wavelength during pulse duration tuning. The developed algorithm enables the user to harness the operational flexibility from such a laser with 'push-button' simplicity. (C) 2012 Optical Society of America

General information

State: Published
Organisations: School of Physics and Astronomy, Univ Glasgow, Sch Phys & Astron, SUPA, Univ Cambridge, Dept Engn, Div Elect
Authors: Metzger, N. K., Olle, V. F., Wonfor, A., Penty, R. V., White, I. H., Mazilu, M., Brown, C. T. A., Sibbett, W.
Keywords:  (Semiconductor lasers, Mode-locked lasers, Laser stabilization)
Number of pages: 13
Pages: 7022-7034
Publication date: 26 Mar 2012
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 20
Issue number: 7
ISSN (Print): 1094-4087
Original language: English
Electronic versions: 
Source: WOS
Source-ID: 000302138800021

Research output: Contribution to journalArticle

Bidirectional Optical Sorting of Gold Nanoparticles

We present a generic technique allowing size-based all-optical sorting of gold nanoparticles. Optical forces acting on metallic nanoparticles are substantially enhanced when they are illuminated at a wavelength near the plasmon resonance, as determined by the particle’s geometry. Exploiting these resonances, we realize sorting in a system of two counter-propagating evanescent waves, each at different wavelengths that selectively guide nanoparticles of different sizes in opposite directions. We validate this concept by demonstrating bidirectional sorting of gold nanoparticles of either 150 or 130 nm in diameter from those of 100 nm in diameter within a mixture.

General information

State: Published
Organisations: School of Medicine, School of Physics and Astronomy
Authors: Ploschner, M., Cizmar, T., Mazilu, M., Di Falco, A., Dholakia, K.
Keywords:  (Gold nanoparticle, optical sorting, optical manipulation, counter-propagating geometry, plasmon resonance)
Number of pages: 5
Pages: 1923-1927
Publication date: 26 Mar 2012
Peer-reviewed: Yes

Publication information

Journal: Nano Letters
Volume: 12
Issue number: 4
ISSN (Print): 1530-6984
Original language: English
 

Research output: Contribution to journalArticle

Exploring the ultrashort pulse laser parameter space for membrane permeabilisation in mammalian cells.

The use of ultrashort femtosecond pulsed lasers to effect membrane permeabilisation and initiate both optoinjection and transfection of cells has recently seen immense interest. We investigate femtosecond laser-induced membrane permeabilisation in mammalian cells as a function of pulse duration, pulse energy and number of pulses, by quantifying the efficiency of optoinjection for these parameters. Depending on pulse duration and pulse energy we identify two distinct membrane permeabilisation regimes. In the first regime a nonlinear dependence of order 3.4-9.6 is exhibited below a threshold peak power of at least 6 kW. Above this threshold peak power, the nonlinear dependence is saturated resulting in linear behaviour. This indicates that the membrane permeabilisation mechanism requires efficient multiphoton absorption to produce free electrons but once this process saturates, linear absorption dominates. Our experimental findings support a previously proposed theoretical model and provide a step towards the optimisation of laser-mediated gene delivery into mammalian cells.

General information

State: Published
Organisations: School of Biology, Institute of Behavioural and Neural Sciences, Biomedical Sciences Research Complex, School of Physics and Astronomy
Authors: Rudhall, A. P., Antkowiak, M., Tsampoula, X., Mazilu, M., Metzger, N. K., Gunn-Moore, F. J., Dholakia, K.
Keywords:  (Ultrashort femtosecond pulsed lasers , Membrane permeabilisation , Mammalian cells )
Pages: 1-5
Publication date: 2012
Peer-reviewed: Yes
Early online date: 14 Nov 2012

Publication information

Journal: Nature Science Reports
Volume: 2
Issue number: 858
Original language: English
Electronic versions: 
 

Research output: Contribution to journalArticle

Optical eigenmodes for imaging applications

We decompose the light field in the focal plane of an imaging system into a set of optical eigenmodes. Subsequently, the superposition of these eigenmodes is identified, that optimizes certain aspects of the imaging process. In practice, the optical eigenmodes modes are implemented using a liquid crystal spatial light modulator. The optical eigenmodes of a system can be determined fully experimentally, taking aberrations into account. Alternatively, theoretically determined modes can be encoded on an aberration corrected spatial light modulator. Both methods are shown to be feasible for applications. To achieve subdiffractive light focussing, optical eigenmodes are superimposed to minimize the width of the focal spot within a small region of interest. In conjunction with a confocal-like detection process, these spots can be utilized for laser scanning imaging. With optical eigenmode engineered spots we demonstrate enhanced two-point resolution compared to the diffraction limited focus and a Bessel beam. Furthermore, using a first order ghost imaging technique, optical eigenmodes can be used for phase sensitive indirect imaging. Numerically we show the phase sensitivity by projecting optical eigenmodes onto a Laguerre-Gaussian target with a unit vortex charge. Experimentally the method is verified by indirect imaging of a transmissive sample.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Kosmeier, S., Mazilu, M., De Luca, A. C., Baumgartl, J., Dholakia, K.
Keywords:  (Optical eigenmodes, Spatial light modulator, Structured light, Beam shaping, Pupil filter, Imaging, Confocal, Superresolution, Image processing, Holography, LATERAL RESOLUTION, MICROSCOPY, LIMIT)
Number of pages: 6
Publication date: 2012

Host publication information

Title of host publication: COMPLEX LIGHT AND OPTICAL FORCES VI
Publisher: SPIE-The International Society for Optical Engineering
Editors: Galvez, E., Andrews, D., Gluckstad, J., Soskin, M.

Publication series

Name: Proceedings of SPIE
Publisher: SPIE-INT SOC OPTICAL ENGINEERING
Volume: 8274
ISSN (Print): 0277-786X
Source: WOS
Source-ID: 000301054600013

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1.6. 2011

Enhanced two-point resolution using optical eigenmode optimized pupil functions

Pupil filters have the capability to arbitrarily narrow the central lobe of a focal spot. We decompose the focal field of a confocal-like imaging system into optical eigenmodes to determine optimized pupil functions, that deliver superresolving scanning spots. As a consequence of this process, intensity is redistributed from the central lobe into side lobes restricting the field of view (FOV). The optical eigenmode method offers a powerful way to determine optimized pupil functions. We carry out a comprehensive study to investigate the relationship between the size of the central lobe, its intensity, and the FOV with the use of a dual display spatial light modulator. The experiments show good agreement with theoretical predictions and numerical simulations. Utilizing an optimized sub-diffraction focal spot for confocal-like scanning imaging, we experimentally demonstrate an improvement of the two-point resolution of the imaging system. © 2011 IOP Publishing Ltd.

General information

State: Published
Organisations: The University of St Andrews, School of Physics and Astronomy
Authors: Kosmeier, S., Mazilu, M., Baumgartl, J., Dholakia, K.
Keywords:  (Pupil filter, Spatial light modulator, Imaging, Optimization)
Number of pages: 9
Publication date: 22 Sep 2011
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics
Volume: 13
Issue number: 10
Article number: 105707
ISSN (Print): 2040-8978
Original language: English

Bibliographical note

Funding: UK EPSRC

Source: Scopus
Source-ID: 80053894650

Research output: Contribution to journalArticle

Optical eigenmode imaging

We present an indirect imaging method that measures both amplitude and phase information from a transmissive target. Our method is based on an optical eigenmode decomposition of the light intensity and the first-order cross correlation between a target field and these eigenmodes. We demonstrate that such optical eigenmode imaging does not need any a priori knowledge of the imaging system and corresponds to a compressive full-field sampling, leading to high image extraction efficiencies. Finally, we discuss the implications with respect to second-order correlation imaging.

General information

State: Published
Organisations: School of Physics and Astronomy, Univ St Andrews, Sch Phys & Astron, SUPA
Authors: De Luca, A. C., Kosmeier, S., Dholakia, K., Mazilu, M.
Number of pages: 4
Pages: -
Publication date: 15 Aug 2011
Peer-reviewed: Yes

Publication information

Journal: Physical Review. A, Atomic, molecular, and optical physics
Volume: 84
Issue number: 2
Article number: 021803
ISSN (Print): 1050-2947
Original language: English
Source: WOS
Source-ID: 000293827400002

Research output: Contribution to journalArticle

Numerical investigation of passive optical sorting of plasmon nanoparticles

We explore the passive optical sorting of plasmon nanoparticles and investigate the optimal wavelength and optimal beam shape of incident field. The condition for optimal wavelength is found by maximising the nanoparticle separation whilst minimising the temperature increase in the system. We then use the force optical eigenmode (FOEi) method to find the beam shape of incident electromagnetic field, maximising the force difference between plasmon nanoparticles. The maximum force difference is found with respect to the whole sorting region. The combination of wavelength and beam shape study is demonstrated for a specific case of gold nanoparticles of radius 40 nm and 50 nm respectively. The optimum wavelength for this particular situation is found to be above 700 nm. The optimum beam shape depends upon the size of sorting region and ranges from plane-wave illumination for infinite sorting region to a field maximising gradient force difference in a single point. (C) 2011 Optical Society of America

General information

State: Published
Organisations: School of Physics and Astronomy, School of Medicine
Authors: Ploschner, M., Mazilu, M., Cizmar, T., Dholakia, K.
Number of pages: 12
Pages: 13922-13933
Publication date: 6 Jul 2011
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 19
Issue number: 15
ISSN (Print): 1094-4087
Original language: English
Electronic versions: 

Bibliographical note

Funding: UK Engineering and Physical Sciences Research Council for funding, KD is a Royal Society-Wolfson Merit Award Holder.

 

Research output: Contribution to journalArticle

Observation and simulation of an optically driven micromotor

In the realm of low Reynolds number flow there is a need to find methods to pump, move and mix minute amounts of analyte. Interestingly, micro-devices performing such actuation can be initiated by means of the light-matter interaction. Light induced forces and torques are exerted on such micro-objects, which are then driven by the optical gradient or scattering force. Here, different driving geometries can be realized to harness the light induced force. For example, the scattering force enables micro-gears to be operated in a tangential setup where the micromotor rotors are in line with an optical waveguide. The operational geometry we investigate has the advantage that it reduces the complexity of the driving of such a device in a microfluidic environment by delivering the actuating light by means of a waveguide or fiber optic. In this paper we explore the case of a micromotor being driven by a fiber optically delivered light beam. We experimentally investigate how the driving light interacts with and diffracts from the motor, utilizing two-photon imaging. The micromotor rotation rate dependence on the light field parameters is explored. Additionally, a theoretical model based on the paraxial approximation is used to simulate the torque and predict the rotation rate of such a device and compare it with experiment. The results presented show that our model can be used to optimize the micromotor performance and some example motor designs are evaluated.

General information

State: Published
Organisations: School of Physics and Astronomy, Biol Res Ctr
Authors: Metzger, N. K., Mazilu, M., Kelemen, L., Ormos, P., Dholakia, K.
Keywords:  (Micromotor, Light-matter interaction, Microfluidics, Lab-on-a-chip, Radiation pressure, Single, Force, Trap, Manipulation, Momentum, Light)
Number of pages: 6
Publication date: 4 Mar 2011
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics
Volume: 13
Issue number: 4
Article number: 044018
ISSN (Print): 2040-8978
Original language: English
Source: WOS
Source-ID: 000291926500019

Research output: Contribution to journalArticle

Modulated Raman spectroscopy for enhanced identification of bladder tumor cells in urine samples

Standard Raman spectroscopy (SRS) is a noninvasive technique that is used in the biomedical field to discriminate between normal and cancer cells. However, the presence of a strong fluorescence background detracts from the use of SRS in real-time clinical applications. Recently, we have reported a novel modulated Raman spectroscopy (MRS) technique to extract the Raman spectra from the background. In this paper, we present the first application of MRS to the identification of human urothelial cells (SV-HUC-1) and bladder cancer cells (MGH) in urine samples. These results are compared to those obtained by SRS. Classification using the principal component analysis clearly shows thatMRS allows discrimination between Raman spectra of SV-HUC-1 andMGH cells with high sensitivity (98%) and specificity (95%). MRS is also used to distinguish between SV-HUC-1 and MGH cells after exposure to urine for up to 6 h.We observe a marked change in the MRS of SV-HUC-1 and MGH cells with time in urine, indicating that the conditions of sample collection will be important for the application of this methodology to clinical urine samples.

General information

State: Published
Organisations: School of Medicine, School of Physics and Astronomy
Authors: Canetta, E., Mazilu, M., De Luca, A. C., Carruthers, A. E., Dholakia, K., Neilson, S., Sargeant, H., Briscoe, T., Herrington, C. S., Riches, A. C.
Keywords:  (Raman spectroscopy, Modulation spectroscopy, Bladder cancer)
Number of pages: 7
Publication date: Mar 2011
Peer-reviewed: Yes

Publication information

Journal: Journal of Biomedical Optics
Volume: 16
Issue number: 3
Article number: 037002
ISSN (Print): 1083-3668
Original language: English
 

Research output: Contribution to journalArticle

Optical sculpting: trapping through disorder and transfer of orbital angular momentum

In this paper, we explore the propagation of light through disordered material and ask whether we can create an optimal focus in such a scenario. We use the complex modulation of the input light (i.e. modulation in both phase and amplitude) for these studies, implemented by use a spatial light modulator (SLM) and show trapping and manipulation through a static turbid medium. We then extend the system to create a tandem SLM system with an acousto-optic deflector. This has further advantages as we can now not only project light fields into turbid media but can also create interference-free mode superpositions of light fields such as Laguerre-Gaussian (LG) and Bessel modes. This is illustrated by controlled rotation of trapped particles in weighted, interference-free superpositions of LG beams of opposite order but equal magnitude.

General information

State: Published
Organisations: School of Physics and Astronomy, School of Medicine, School of Biology, Institute of Behavioural and Neural Sciences, Biomedical Sciences Research Complex
Authors: Cizmar, T., Mazilu, M., Dalgarno, H., Ashok, P., Gunn-Moore, F., Dholakia, K.
Keywords:  (Coherence, Interference, Diffraction, optical vortex, trapping, optical tweezers, LIGHT, BEAMS)
Number of pages: 7
Pages: 79500R
Publication date: 3 Feb 2011

Host publication information

Title of host publication: Complex Light and Optical Forces V
Publisher: SPIE
Editors: Andrews, D. L., Galvez, E. J., Gluckstad, J.
ISBN (Print): 978-0-81948-487-1

Publication series

Name: Proceedings of SPIE
Volume: 7950
ISSN (Print): 0277-786X
Source: WOS
Source-ID: 000293699600022

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Optical Eigenmodes; exploiting the quadratic nature of the energy flux and of scattering interactions

We report a mathematically rigorous technique which facilitates the optimization of various optical properties of electromagnetic fields in free space and including scattering interactions. The technique exploits the linearity of electromagnetic fields along with the quadratic nature of the intensity to define specific Optical Eigenmodes (OEi) that are pertinent to the interaction considered. Key applications include the optimization of the size of a focused spot, the transmission through sub-wavelength apertures, and of the optical force acting on microparticles. We verify experimentally the OEi approach by minimising the size of a focused optical field using a superposition of Bessel beams. (C) 2011 Optical Society of America

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Mazilu, M., Baumgartl, J., Kosmeier, S., Dholakia, K.
Keywords:  (Light, Beams)
Number of pages: 13
Pages: 933-945
Publication date: 17 Jan 2011
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 19
Issue number: 2
ISSN (Print): 1094-4087
Original language: English
Electronic versions: 
Source: WOS
Source-ID: 000286314600054

Research output: Contribution to journalArticle

Enhanced bioanalyte detection in waveguide confined Raman spectroscopy using wavelength modulation

Waveguide confined Raman spectroscopy (WCRS) incorporates a fibre based Raman detection system in a microfluidic platform enabling the spectroscopic detection of analyte. It offers the possibility to develop portable, alignment free devices for bio-analyte sensing with minimal sample preparation. Ultimate sensitivity is limited by the fibre auto-fluorescence background. Here we report enhanced bio-analyte detection sensitivity by combining WCRS with continuous wavelength modulation technique. We used urea as a model analyte and the modulation parameters have been optimized to maximize the sensitivity of the device.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Ashok, P. C., De Luca, A. C., Mazilu, M., Dholakia, K.
Keywords:  (raman spectroscopy, microfluidics, analyte detection , fluorescent suppression)
Number of pages: 5
Publication date: 2011
Peer-reviewed: Yes
Early online date: 24 Jan 2011

Publication information

Journal: Journal of Biophotonics
ISSN (Print): 1864-063X
Original language: English
 

Research output: Contribution to journalArticle

1.7. 2010

Optical path clearing and enhanced transmission through colloidal suspensions

We utilize advanced laser fields to clear a path through a dynamic turbid medium, a concept termed "Optical path clearing (OPC)." Particles are evacuated from a volume of the medium using the gradient and/or scattering forces due to an applied laser field with a suitably tailored spatial profile. Our studies encompass both an analytical model and proof-of-principle experiments where paths are cleared in dense bulk colloidal suspensions. Based on our results we suggest that high-performance and high efficiency OPC will be achieved by multiple-step clearing using dynamic laser fields based on Airy or inverted axicon beams. (C) 2010 Optical Society of America

General information

State: Published
Organisations: School of Medicine, School of Physics and Astronomy, The University of St Andrews, Boeing Res & Technol
Authors: Baumgartl, J., Cizmar, T., Mazilu, M., Chan, V. C., Carruthers, A. E., Capron, B. A., McNeely, W., Wright, E. M., Dholakia, K.
Keywords:  (ORBITAL ANGULAR-MOMENTUM, AIRY BEAMS, MANIPULATION, PARTICLES, TRANSFORMATION, LIGHT)
Number of pages: 11
Pages: 17130-17140
Publication date: 2 Aug 2010
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 18
Issue number: 16
ISSN (Print): 1094-4087
Original language: English
Links: 
Source: WOS
Source-ID: 000281042400088

Research output: Contribution to journalArticle

In situ wavefront correction and its application to micromanipulation

In any optical system, distortions to a propagating wavefront reduce the spatial coherence of a light field, making it increasingly difficult to obtain the theoretical diffraction-limited spot size. Such aberrations are severely detrimental to optimal performance in imaging, nanosurgery, nanofabrication and micromanipulation, as well as other techniques within modern microscopy. We present a generic method based on complex modulation for true in situ wavefront correction that allows compensation of all aberrations along the entire optical train. The power of the method is demonstrated for the field of micromanipulation, which is very sensitive to wavefront distortions. We present direct trapping with optimally focused laser light carrying power of a fraction of a milliwatt as well as the first trapping through highly turbid and diffusive media. This opens up new perspectives for optical micromanipulation in colloidal and biological physics and may be useful for various forms of advanced imaging.

General information

State: Published
Organisations: School of Physics and Astronomy, School of Medicine
Authors: Cizmar, T., Mazilu, M., Dholakia, K.
Keywords:  (HOLOGRAPHIC OPTICAL TWEEZERS, ABERRATION CORRECTION, ADAPTIVE OPTICS, LIGHT, LASER, IMAGE, RESOLUTION, BESSEL, MEDIA, BEAMS)
Number of pages: 7
Pages: 388-394
Publication date: Jun 2010
Peer-reviewed: Yes
Early online date: 9 May 2010

Publication information

Journal: Nature Photonics
Volume: 4
Issue number: 6
ISSN (Print): 1749-4885
Original language: English
Source: WOS
Source-ID: 000278422200017

Research output: Contribution to journalArticle

Optimal algorithm for fluorescence suppression of modulated Raman spectroscopy

Raman spectroscopy permits probing of the molecular and chemical properties of the analyzed sample. However, its applicability has been seriously limited to specific applications by the presence of a strong fluorescence background. In our recent paper [Anal. Chem. 82, 738 (2010)], we reported a new modulation method for separating Raman scattering from fluorescence. By continuously changing the excitation wavelength, we demonstrated that it is possible to continuously shift the Raman peaks while the fluorescence background remains essentially constant. In this way, our method allows separation of the modulated Raman peaks from the static fluorescence background with important advantages when compared to previous work using only two [Appl. Spectrosc. 46, 707 (1992)] or a few shifted excitation wavelengths [Opt. Express 16, 10975 (2008)]. The purpose of the present work is to demonstrate a significant improvement of the efficacy of the modulated method by using different processing algorithms. The merits of each algorithm (Standard Deviation analysis, Fourier Filtering, Least-Squares fitting and Principal Component Analysis) are discussed and the dependence of the modulated Raman signal on several parameters, such as the amplitude and the modulation rate of the Raman excitation wavelength, is analyzed. The results of both simulation and experimental data demonstrate that Principal Component Analysis is the best processing algorithm. It improves the signal-to-noise ratio in the treated Raman spectra, reducing required acquisition times. Additionally, this approach does not require any synchronization procedure, reduces user intervention and renders it suitable for real-time applications. (C) 2010 Optical Society of America

General information

State: Published
Organisations: School of Physics and Astronomy, School of Medicine
Authors: Mazilu, M., De Luca, A. C., Riches, A., Herrington, C. S., Dholakia, K.
Keywords:  (MICROSCOPY, REJECTION, CELLS, DIFFUSION, PARTICLES, NEOPLASIA, TWEEZERS, TOOL)
Number of pages: 14
Pages: 11382-11395
Publication date: 24 May 2010
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 18
Issue number: 11
ISSN (Print): 1094-4087
Original language: English
Source: WOS
Source-ID: 000278512300053

Research output: Contribution to journalArticle

Optical forces near a nanoantenna

The Maxwell stress tensor method is used to calculate the optical forces acting upon a glass nanosphere in the proximity of optically excited gold nanoantenna structures. The dependence of optical forces over a full range of excitation angles is explored: the total internal reflection excitation does not bring any particular advantage to trapping efficiency when compared to the normal incidence excitation. Our calculations show multiple trapping sites with similar trapping properties for the normal and the total internal reflection cases, respectively; furthermore, the convective heating probably dominates over any optical forces in such systems.

General information

State: Published
Organisations: School of Physics and Astronomy, Microphotonics and Photonic Crystals Group
Authors: Ploschner, M., Mazilu, M., Krauss, T. F., Dholakia, K.
Keywords:  (Force, Trapping, Nanoantenna, Maxwell stress tensor, Torque, field)
Number of pages: 13
Publication date: 4 Feb 2010
Peer-reviewed: Yes

Publication information

Journal: Journal of Nanophotonics
Volume: 4
Article number: 041570
ISSN (Print): 1934-2608
Original language: English

Bibliographical note

Partially funded by UK EPSRC

Source: WOS
Source-ID: 000278050500001

Research output: Contribution to journalArticle

Online Fluorescence Suppression in Modulated Raman Spectroscopy

Label-free chemical characterization of single cells is an important aim for biomedical research. Standard Raman spectroscopy provides intrinsic biochemical markers for noninvasive analysis of biological samples but is often hindered by the presence of fluorescence background. In this paper, we present an innovative modulated Raman spectroscopy technique to filter out the Raman spectra from the fluorescence background. The method is based on the principle that the fluorescence background does not change whereas the Raman scattering is shifted by the periodical modulation of the laser wavelength. Exploiting this physical property and importantly the multichannel lock-in detection of the Raman signal, the modulation technique fulfills the requirements of an effective fluorescence subtraction method. Indeed, once the synchronization and calibration procedure is performed, minimal user intervention is required, making the method online and less time-consuming than the other fluorescent suppression methods. We analyze the modulated Raman signal and shifted excitation Raman difference spectroscopy (SERDS) signal of 2 pm-sized polystyrene beads suspended in a solution of fluorescent dye its a function of modulation rate. We show that the signal-to-noise ratio of the modulated Raman spectra at the highest modulation rate is 3 times higher than the SERDS one. To finally evaluate the real benefits of the modulated Raman spectroscopy, we apply our technique to Chinese hamster ovary cells (CHO). Specifically, by analyzing separate spectra from the membrane, cytoplasm, and nucleus of CHO cells, we demonstrate the ability of this method to obtain localized sensitive chemical information from cells, away from the interfering fluorescence background. In particular, statistical analysis of the Raman data and classification using PCA (principal component analysis) indicate that our method allows us to distinguish between different cell locations with higher sensitivity and specificity, avoiding potential misinterpretation of the data obtained using standard background procedures.

General information

State: Published
Organisations: School of Medicine, School of Physics and Astronomy
Authors: De Luca, A. C., Mazilu, M., Riches, A. C., Herrington, C. S., Dholakia, K.
Keywords:  (CELLS, MICROSPECTROSCOPY, REJECTION, TWEEZERS, SPECTRA, INTERFERENCE, NEOPLASIA, PHASE, LASER)
Number of pages: 8
Pages: 738-745
Publication date: 15 Jan 2010
Peer-reviewed: Yes

Publication information

Journal: Analytical Chemistry
Volume: 82
Issue number: 2
ISSN (Print): 0003-2700
Original language: English
Source: WOS
Source-ID: 000273484200041

Research output: Contribution to journalArticle

Fluorescence background suppression in Raman spectroscopy

Raman spectroscopy provides a non-invasive method to study biological samples. We demonstrate the powerful capabilities of our novel Raman modulation technique to detect weak Raman signals hidden by a strong fluorescent background. (C)2010 Optical Society of America

General information

State: Published
Organisations: School of Medicine, School of Physics and Astronomy, Univ Birmingham, Sch Phys & Astron
Authors: Mazilu, M., De Luca, A. C., Riches, A., Herrington, S., Dholakia, K.
Number of pages: 2
Pages: -
Publication date: 2010

Host publication information

Title of host publication: 2010 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) AND QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (QELS)
Place of publication: NEW YORK
Publisher: IEEE
ISBN (Print): 978-1-55752-890-2
Source: WOS
Source-ID: 000290513601124

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Fluorescence-Free Biochemical Characterization of Cells Using Modulated Raman Spectroscopy

General information

State: Published
Organisations: School of Medicine, School of Physics and Astronomy, Univ St Andrews, Sch Phys & Astron, SUPA
Authors: De Luca, A. C., Mazilu, M., Riches, A., Herrington, S., Dholakia, K.
Number of pages: 2
Pages: 227-228
Publication date: 2010

Host publication information

Title of host publication: XXII INTERNATIONAL CONFERENCE ON RAMAN SPECTROSCOPY
Place of publication: MELVILLE
Publisher: AMER INST PHYSICS
Editors: Champion, P., Ziegler, L.
ISBN (Print): 978-0-7354-0818-0
Source: WOS
Source-ID: 000281210900125

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Fluorescence-free biochemical characterization of cells using modulated Raman spectroscopy

The use of Raman spectroscopy for biomedical applications requires overcoming the obstacle of the broad fluorescence background that is generally generated in biological samples. Recently, we have developed a new modulation method for separating the weak Raman peaks from the strong fluorescence background. The novel method is based on the periodical modulation of the excitation wavelength and uses the principle of multi-channel lock-in detection. By continuously modulating the excitation wavelength it is possible to shift the Raman peaks while the fluorescence background remains essentially constant. The powerful capabilities of this novel method are demonstrated by acquiring spectra from different location (nucleus, cytoplasm and membrane) inside a CHO cell. In fact, we show that our modulated Raman spectroscopy provides, with higher efficiency than the standard one, Raman spectra of different locations within a single cell, suggesting that this minimally invasive optical technology could be applied for bio-medical diagnosis and imaging.

General information

State: Published
Organisations: School of Medicine, School of Physics and Astronomy, Univ Birmingham, Sch Phys & Astron
Authors: De Luca, A. C., Mazilu, M., Riches, A., Herrington, S., Dholakia, K.
Number of pages: 6
Pages: -
Publication date: 2010

Host publication information

Title of host publication: ADVANCED BIOMEDICAL AND CLINICAL DIAGNOSTIC SYSTEMS VIII
Place of publication: BELLINGHAM
Publisher: SPIE-The International Society for Optical Engineering
Editors: VoDinh, T., Grundfest, W., MahadevanJansen, A.
ISBN (Print): 978-0-8194-7951-8
Source: WOS
Source-ID: 000284396000023

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Modulated Raman spectroscopy technique for 'real-time' fluorescence rejection

Raman spectroscopy is a label-free and non-invasive method that measures the inelastic scattered light from a sample giving insight into the vibration eigenmodes of the excited molecules. Raman spectroscopy provides a detailed chemical composition of the sample, constituting a sort of its chemical fingerprint. Although Raman spectroscopy is a useful technique to identify and quantify species in a given matrix, it has been severely limited in its applicability by fluorescence. Spectrally, this fluorescence occurs at the same wavelength as the Raman signal and is often several orders of magnitude more intense that the weak chemical transitions probed by Raman spectroscopy. Often, this fluorescence background and its natural variability make biochemical analysis using Raman spectroscopy impractical. In this work, we present the theory and the implementation of an innovative modulated Raman spectroscopy technique to filter out the Raman spectra from the fluorescence background by modulating of the excitation wavelength. The method is based on the continuous wavelength shift of the Raman peaks with the modulation of the laser wavelength while the fluorescence background remains static. Exploiting this physical property allows us to clearly distinguish between the Raman signal and the fluorescence background. Our method is related to wavelength shifting Raman spectroscopy but incorporates two key novel elements: (i) the use of more than two excitation wavelengths and (ii) multi-channel lock-in detection of the Raman signal for suppression of the fluorescence background. Our results establish a direct and practical approach for fluorescence background suppression in 'real-time' Raman spectroscopy for in-vivo biomedical applications.

General information

State: Published
Organisations: School of Medicine, School of Physics and Astronomy, Univ Strathclyde, SUPA
Authors: Mazilu, M., De Luca, A. C., Riches, A., Herrington, S., Dholakia, K.
Number of pages: 5
Pages: -
Publication date: 2010

Host publication information

Title of host publication: IMAGING, MANIPULATION, AND ANALYSIS OF BIOMOLECULES, CELLS, AND TISSUES VIII
Place of publication: BELLINGHAM
Publisher: SPIE-The International Society for Optical Engineering
Editors: Farkas, D., Nicolau, D., Leif, R.
ISBN (Print): 978-0-8194-7964-8
Source: WOS
Source-ID: 000284359700014

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Optical Sculpting: Shaping the Future of Biophotonics

We describe the topic of beam shaping (sculpting) the phase and amplitude of light for applications in Biophotonics. Methods to create and apply 'non-diffracting' modes in cell transfection and micromanipulation will be discussed as well as a new method to correct for aberrations in situ and overcome the diffraction limit.

General information

State: Published
Organisations: School of Physics and Astronomy, School of Medicine, School of Biology, Institute of Behavioural and Neural Sciences, Biomedical Sciences Research Complex
Authors: Dholakia, K., Cizmar, T., Mazilu, M., Baumgartl, J., Tsampoula, X., Gunn-Moore, F.
Keywords:  (Optical trapping, photoporation, cell transfection, wavefront correction, diffraction, MICROMANIPULATION)
Number of pages: 2
Pages: 1-2
Publication date: 2010

Host publication information

Title of host publication: Third International Workshop on Theoretical and Computational Nano-Photonics (TaCoNa-Photonics 2010)
Publisher: American Institute of Physics
Editor: Chigrin, D. N.
ISBN (Print): 978-0-7354-0846-3

Publication series

Name: AIP Conference Proceedings
Volume: 1291
ISSN (Print): 0094-243X
Source: WOS
Source-ID: 000287019200001

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1.8. 2009

Propagation characteristics of Airy beams: dependence upon spatial coherence and wavelength

We generate a broadband "white light" Airy beam and characterize the dependence of the beam properties on wavelength. Experimental results are presented showing that the beam's deflection coefficient and its characteristic length are wavelength dependent. In contrast the aperture coefficient is not wavelength dependent. However, this coefficient depends on the spatial coherence of the beam. We model this behaviour theoretically by extending the Gaussian-Schell model to describe the effect of spatial coherence on the propagation of Airy beams. The experimental results are compared to the model and good agreement is observed. (C) 2009 Optical Society of America

General information

State: Published
Organisations: School of Medicine, School of Physics and Astronomy
Authors: Morris, J. E., Mazilu, M., Baumgartl, J., Cizmar, T., Dholakia, K.
Number of pages: 10
Pages: 13236-13245
Publication date: 20 Jul 2009
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 17
Issue number: 15
ISSN (Print): 1094-4087
Original language: English
Source: WOS
Source-ID: 000268399500106

Research output: Contribution to journalArticle

Spin and angular momentum operators and their conservation

Lorentz's reciprocity lemma and the Feld-Tai reciprocity theorem show the effect of interchanging the action and reaction in Maxwell's equations. We derive a free space version of these reciprocity relations which generalizes the conservation of the momentum-energy tensor. This relation corresponds to the interference conservation of electromagnetic waves. We show that for any transformation or symmetry that leaves Maxwell's equations invariant, we can modify the reciprocity relation to introduce conserved density, optical flux and stress tensor, applying Noether's theorem in a different context. We apply this method to transformations that can be expressed as Hermitian operators and, more specifically, we define the operators associated with the optical energy, spin, linear and angular momentum.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Mazilu, M.
Keywords:  (Conserving currents, Spin density, Orbital angular momentum density, Eigenmodes, Electromagnetic theory, Paraxial beams, Light, Reciprocity, Fields)
Number of pages: 4
Publication date: 27 Apr 2009
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics A: Pure and Applied Optics
Volume: 11
Issue number: 9
Article number: 094005
ISSN (Print): 1464-4258
Original language: English
Source: WOS
Source-ID: 000268692600007

Research output: Contribution to journalArticle

1.9. 2008

Optically mediated particle clearing using Airy wavepackets

The Airy wavepacket solution for a free particle exhibits propagation invariance and, surprisingly, acceleration transverse to the propagation direction(1). Discovered as a solution of the free-particle Schrodinger equation, Airy wavepackets have been predicted(2), and in a recent major step forward, realized(3) in the optical domain, but have never been used in any application. In this Letter we demonstrate the first use of the Airy light beam in optical micromanipulation(4,5). Based on the characteristic intensity pattern, the beam drags particles into the main intensity maximum, which guides particles vertically along a parabolic trajectory. This unusual property of Airy beams leads to a new feature in optical micromanipulation-the removal of particles and cells from a section of a sample chamber. We term this highly robust and efficient process 'optically mediated particle clearing', which enables novel microfluidic applications within the colloidal and biological sciences.

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews
Authors: Baumgartl, J., Mazilu, M., Dholakia, K.
Keywords:  (LIGHT-BEAM, MICROMANIPULATION)
Number of pages: 4
Pages: 675-678
Publication date: Nov 2008
Peer-reviewed: Yes

Publication information

Journal: Nature Photonics
Volume: 2
Issue number: 11
ISSN (Print): 1749-4885
Original language: English
Source: WOS
Source-ID: 000261004900013

Research output: Contribution to journalArticle

Guided neuronal growth using optical line traps

Optically guided neuron growth is a relatively new field where the exact mechanisms that initiate growth are not well understood. Both Gaussian light beams and optical line traps have been purported to initiate neuronal growth. Here we present a detailed study using optical line traps with symmetric and asymmetric intensity profiles which have been previously reported to bias the direction of neuronal growth. In contrast to these previous studies, we show similar levels of growth regardless of the direction of the intensity variation along the line trap. Furthermore, our experimental observations confirm previous suggestions that the filopodia produced from neuronal growth cones can be affected by laser light. We experimentally observe alignment of filopodia with the laser field and present a theoretical model describing the optical torques experienced by filopodia to explain this effect. (c) 2008 Optical Society of America.

General information

State: Published
Organisations: School of Physics and Astronomy, School of Biology
Authors: Carnegie, D., Stevenson, D., Mazilu, M., Gunn-Moore, F. J., Dholakia, K.
Keywords:  (GUIDANCE, DYNAMICS, LIGHT)
Number of pages: 11
Pages: 10507-10517
Publication date: 7 Jul 2008
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 16
Issue number: 14
ISSN (Print): 1094-4087
Original language: English
Source: WOS
Source-ID: 000257564100057

Research output: Contribution to journalArticle

Optical micromanipulation using supercontinuum Laguerre-Gaussian and Gaussian beams

We characterize a single beam supercontinuum "white light" trap and determine the trap stiffness in the transverse trapping plane. We realize a holographic white light trapping system using a spatial light modulator, and explore the generation of a dual beam trap and characterize its performance. We also demonstrate optical trapping and rotation of particles using a supercontinuum vortex beam. It is shown that orbital angular momentum can be transferred to spheres trapped in a supercontinuum vortex. Quantified rotation rates are demonstrated. (C) 2008 Optical Society of America.

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews, Scottish Universities Physics Alliance
Authors: Morris, J. E., Carruthers, A. E., Mazilu, M., Reece, P. J., Cizmar, T., Fischer, P., Dholakia, K.
Keywords:  (COMPUTER-GENERATED HOLOGRAMS, ORBITAL ANGULAR-MOMENTUM, PARTICLES, TWEEZERS, LIGHT, MANIPULATION, SPHERES, MODES, TRAP)
Number of pages: 13
Pages: 10117-10129
Publication date: 7 Jul 2008
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 16
Issue number: 14
ISSN (Print): 1094-4087
Original language: English
Source: WOS
Source-ID: 000257564100012

Research output: Contribution to journalArticle

Simulated holographic three-dimensional intensity shaping of evanescent-wave fields

The size of bright structures in traveling-wave light fields is limited by diffraction. This in turn limits a number of technologies, for example, optical trapping. One way to beat the diffraction limit is to use evanescent waves instead of traveling waves. Here we apply a holographic algorithm, direct search, to the shaping of complex evanescent-wave fields. We simulate three-dimensional intensity shaping of evanescent-wave fields using this approach, and we investigate some of its limitations. (c) 2008 Optical Society of America.

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews, Dept Phys & Astron, Dept Chem Engn
Authors: Thomson, L. C., Whyte, G., Mazilu, M., Courtial, J.
Keywords:  (PERFECT LENS, SEARCH)
Number of pages: 5
Pages: 849-853
Publication date: May 2008
Peer-reviewed: Yes

Publication information

Journal: Journal of the Optical Society of America B : Optical Physics
Volume: 25
Original language: English
Source: WOS
Source-ID: 000256323200021

Research output: Contribution to journalArticle

Optical vortex trap for resonant confinement of metal nanoparticles

The confinement and controlled movement of metal nanoparticles and nanorods is an emergent area within optical micromanipulation. In this letter we experimentally realise a novel trapping geometry near the plasmon resonance using an annular light field possessing a helical phasefront that confines the nanoparticle to the vortex core (dark) region. We interpret our data with a theoretical framework based upon the Maxwell stress tensor formulation to elucidate the total forces upon nanometric particles near the particle plasmon resonance. Rotation of the particle due to orbital angular momentum transfer is observed. This geometry may have several advantages for advanced manipulation of metal nanoparticles. (C) 2008 Optical Society of America.

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews
Authors: Dienerowitz, M., Mazilu, M., Reece, P., Krauss, T. F., Dholakia, K.
Keywords:  (ORBITAL ANGULAR-MOMENTUM, GAUSSIAN LASER MODES, GOLD NANOPARTICLES, RADIATION PRESSURE, PARTICLES, SINGLE, SPECTROSCOPY, FORCES, ATOMS, LIGHT)
Number of pages: 9
Pages: 4991-4999
Publication date: 31 Mar 2008
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 16
Issue number: 7
ISSN (Print): 1094-4087
Original language: English
Source: WOS
Source-ID: 000255100400065

Research output: Contribution to journalArticle

Optical deflection and sorting of microparticles in a near-field optical geometry

Near- field optical micromanipulation permits new possibilities for controlled motion of trapped objects. In this work, we report an original geometry for optically deflecting and sorting micro- objects employing a total internal reflection microscope system. A small beam of laser light is delivered off- axis through a total internal reflection objective which creates an elongated evanescent illumination of light at a glass/ water interface. Asymmetrical gradient and scattering forces from this light field are seen to deflect and sort polystyrene microparticles within a fluid flow. The speed of the deflected objects is dependent upon their intrinsic properties. We present a finite element method to calculate the optical forces for the evanescent waves. The numerical simulations are in good qualitative agreement with the experimental observations and elucidate features of the particle trajectory. In the size range of 1 mu m to 5 mu m in diameter, polystyrene spheres were found to be guided on average 2.9 +/- 0.7 faster than silica spheres. The velocity increased by 3.0 +/- 0.5 mu ms(-1) per mu m increase in diameter for polystyrene spheres and 0.7 +/- 0.2 mu ms(-1) per mu m for silica. We employ this size dependence for performing passive optical sorting within a microfluidic chip and is demonstrated in the accompanying video.

(C) 2008 Optical Society of America.

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews, Microphotonics and Photonic Crystals Group, Fac Engn & Ind Sci
Authors: Marchington, R. F., Mazilu, M., Kuriakose, S., Garces-Chavez, V., Reece, P. J., Krauss, T. F., Gu, M., Dholakia, K.
Keywords:  (EVANESCENT-WAVE ILLUMINATION, POTENTIAL-ENERGY LANDSCAPES, MICROMETER-SIZED SPHERE, RADIATION FORCES, SHEAR-FLOW, PLANE WALL, PARTICLE, CHROMATOGRAPHY, SEPARATION, MOTION)
Number of pages: 15
Pages: 3712-3726
Publication date: 17 Mar 2008
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 16
Issue number: 6
ISSN (Print): 1094-4087
Original language: English
Source: WOS
Source-ID: 000254121400026

Research output: Contribution to journalArticle

1.10. 2007

The resolution of optical traps created by light induced dielectrophoresis (LIDEP)

Light induced dielectrophoresis ( LIDEP) is a variant of the dielectrophoresis ( DEP) mechanism that has been used for some time to manipulate particles in a microfluidic environment. Rather than relying on lithographically created contacts to generate the required electrical fields, the electrical contacts in LIDEP are created through the selective illumination of a photoconductor. The key question we address is how microscopic traps created via LIDEP compare to optical traps based on the gradient force, in terms of power required and trap stiffness achieved, as well as the size resolution of such a trap. We highlight the complex interplay between optical power and resolution with electrical parameters, such as the electrical resistance and applied AC Voltage. We show that for a spotsize of five micrometres and larger, particles can indeed be trapped with low power. We use trap stiffness per mW to compare LIDEP with an optical trap and show that our system is 470 +/- 94 times stiffer per mW than a conventional optical trap, with no loss of resolution. We also discuss the difficulties of achieving trapping at smaller spot sizes, and that the sub-micron resolution possible with gradient force trapping is very difficult to realise with LIDEP. (C) 2007 Optical Society of America.

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews, Microphotonics and Photonic Crystals Group
Authors: Neale, S. L., Mazilu, M., Wilson, J. I. B., Dholakia, K., Krauss, T. F.
Keywords:  (MANIPULATION)
Number of pages: 8
Pages: 12619-12626
Publication date: 1 Oct 2007
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 15
Issue number: 20
ISSN (Print): 1094-4087
Original language: English
Source: WOS
Source-ID: 000250006700006

Research output: Contribution to journalArticle

Fluorescence suppression within Raman spectroscopy using annular beam excitation

This letter demonstrates how the use of an annular beam can significantly reduce the detected fluorescence from optical components within a Raman spectroscopic arrangement. The fluorescence from the excitation beam has a reduced generation and collection efficiency compared to the standard Gaussian beam. Crucially, the Raman signal from the annular beam is collected through the dark center of the excitation light field. This robust and simple technique may be immediately applied to all Raman configurations and may find broader applicability for any spectroscopic methodology which utilizes a high numerical aperture lens and requires the detected fluorescence to be suppressed. (C) 2007 American Institute of Physics.

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews, School of Medicine
Authors: Cormack, I. G., Mazilu, M., Dholakia, K., Herrington, C. S.
Keywords:  (LIGHT, SERS)
Number of pages: 3
Pages: 023903
Publication date: 9 Jul 2007
Peer-reviewed: Yes

Publication information

Journal: Applied Physics Letters
Volume: 91
Issue number: 2
ISSN (Print): 0003-6951
Original language: English
Source: WOS
Source-ID: 000248017300108

Research output: Contribution to journalArticle

Measurement of the restoring forces acting on two optically bound particles from normal mode correlations

Optical binding along the axis of two counterpropagating laser fields may be used to organize microparticles into longitudinal, spatially separated, arrays. Here we investigate correlations between the displacements of two optically bound microparticles from their equilibrium positions due to noise. Measurement of the decay time of the correlation functions of the center of mass and relative normal modes is shown to provide an in situ method to determine the optical restoring forces acting on the bound particles, thereby providing a test of our physical understanding of longitudinal optical binding.

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews
Authors: Metzger, N. K., Marchington, R. F., Mazilu, M., Smith, R. L., Dholakia, K., Wright, E. M.
Keywords:  (TRAP, BINDING, FIELDS)
Number of pages: 4
Publication date: 9 Feb 2007
Peer-reviewed: Yes

Publication information

Journal: Physical Review Letters
Volume: 98
ISSN (Print): 0031-9007
Original language: English
Source: WOS
Source-ID: 000244117400069

Research output: Contribution to journalArticle

Structural characterization of shock-affected sapphire

The presence of dislocations has been revealed by numerical processing of high-resolution transmission electron microscopy images from the regions affected by a shock wave propagation. The shock wave was triggered by a single 220 fs duration pulse of 30 nJ at an 800 nm wavelength inside sapphire at approximately 10 mu m depth. The shock-amorphised sapphire has a distinct boundary with the crystalline phase, which is not wet etchable even at a dislocation density of similar or equal to 8 x 10(12) cm(-2).

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews
Authors: Mazilu, M., Juodkazis, S., Ebisui, T., Matsuo, S., Misawa, H.
Keywords:  (FEMTOSECOND, GLASS)
Number of pages: 4
Pages: 197-200
Publication date: Feb 2007
Peer-reviewed: Yes

Publication information

Journal: Applied Physics A
Volume: 86
Issue number: 2
ISSN (Print): 0947-8396
Original language: English
Source: WOS
Source-ID: 000242446300009

Research output: Contribution to journalArticle

1.11. 2006

Room temperature electron spin relaxation in GaInNAs multiple quantum wells at 1.3 μm

The authors report a direct measurement of electron spin relaxation in GaInNAs semiconductor multiple quantum wells at room temperature. Multiple quantum wells of widths 5.8, 7, and 8 nm exhibiting excitonic absorption around 1.3 mu m have been studied. Spin relaxation times were found to increase with well width in the range of 77-133 ps. The spin relaxation time dependence on first electron confinement energy suggests the Elliot-Yafet mechanism [A. Tackeuchi , Physica B 272, 318 (1999)] as the dominant relaxation process. (c) 2006 American Institute of Physics.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Reith, C., White, S. J., Mazilu, M., Miller, A., Konttinen, J., Guina, M., Pessa, M.
Number of pages: 3
Pages: 211122
Publication date: 20 Nov 2006
Peer-reviewed: Yes

Publication information

Journal: Applied Physics Letters
Volume: 89
Issue number: 21
ISSN (Print): 0003-6951
Original language: English
Source: WOS
Source-ID: 000242220000022

Research output: Contribution to journalArticle

Dual beam fibre trap for Raman micro-spectroscopy of single cells

Raman spectroscopy permits acquisition of molecular signatures from both cellular and sub-cellular samples. When combined with optical trapping we may interrogate an isolated cell reducing extraneous signals from the local environment. To date, experimental configurations have employed combinations of the single beam optical tweezers trap and Raman spectroscopy, using either the same beam or separate beams for Raman interrogation and trapping. A key problem in optical tweezers is the ability to hold and manoeuvre large cells. In this paper, we use a dual beam fibre trap to hold and manoeuvre cells combined with an orthogonally placed objective to record Raman spectra. The dual beam trap, due to its divergent light fields, offers an as yet unexploited ability to hold and move large cellular objects with reduced prospects of photodamage. We additionally show how this system permits us to move large primary human keratinocytes ( approximately 30 microns in diameter), such that we may record Raman spectra from local parts of a trapped cell with ease. Finally, we develop a rudimentary microfluidic system used to generate a flow of cells. Using our dual beam trap, combined with this flow system, we hold and acquire Raman spectra from individual cells chosen from a sample of HL60 human promyelocytic leukemia cells. (c) 2006 Optical Society of America.

General information

State: Published
Organisations: School of Physics and Astronomy, School of Medicine
Authors: Jess, P., Garces-Chavez, V. G., Smith, D., Mazilu, M., Paterson, L., Riches, A. C., Herrington, C. S., Sibbett, W., Dholakia, K.
Keywords:  (OPTICAL TWEEZERS, LIVING CELLS, SPECTROSCOPY, DIFFERENTIATION, PARTICLES, SYSTEM)
Number of pages: 13
Pages: 5779-5791
Publication date: 12 Jun 2006
Peer-reviewed: Yes

Publication information

Journal: Optics Express
Volume: 14
Issue number: 12
Original language: English
Source: WOS
Source-ID: 000238437800094

Research output: Contribution to journalArticle

Size resolution with Light Induced Dielectrophoresis (LIDEP)

We present a study into the small particle size and resolution limits of Light Induced Dielectrophoresis (LIDEP). Here the illumination of a photoconductive layer creates virtual electrodes whose associated electric field gradients cause the dielectrophoretic response of the particles. In this way a potential energy landscape can be created that is optically controlled giving reconfigurable control over a large area [1]. In this paper we discuss the interlinked limits of size of particle it is possible to manipulate and the resolution these particles can be manipulated with. We compare traditional dielectrophoresis (DEP) experiments with LIDEP experiments, and discuss the mechanisms behind the physical limits comparing the effects of carrier diffusion verses the spreading of the electric fields in the medium.

General information

State: Published
Organisations: School of Physics and Astronomy, Microphotonics and Photonic Crystals Group
Authors: Neale, S. L., Mazilu, M., MacDonald, M. P., Wilson, J. I. B., Dholakia, K., Krauss, T. F.
Keywords:  (Light Induced Dielectrophoresis (UDEP), optoelectronic tweezers, optical tweezers)
Number of pages: 10
Pages: U308-U317
Publication date: 2006

Host publication information

Title of host publication: Optical Trapping and Optical Micromanipulation III
Publisher: SPIE-The International Society for Optical Engineering
Editors: Dholakia, K., Spalding, G.
ISBN (Print): 0-8194-6405-8

Publication series

Name: PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS (SPIE)
Publisher: SPIE-INT SOC OPTICAL ENGINEERING
Volume: 6326
ISSN (Print): 0277-786X
Source: WOS
Source-ID: 000243027100036

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1.12. 2005

Spatial dependence of gain nonlinearities in InGaAs semiconductor optical amplifier

Counter-propagating sub-picosecond pulses are used to monitor gain saturation along the waveguide of an InGaAs superlattice semiconductor optical amplifier at 1550 nm wavelength. The functional form of the spatial dependence of gain saturation is found to depend on pulse energy. These observations are interpreted by combining the optical nonlinearities associated with interband carrier dynamics and carrier heating together and their respective time constants. We show that the results are consistent with the predictions of a propagation model. Implications for all-optical switching, particularly in the limit of full saturation across the whole amplifier, are discussed. (c) 2005 American Institute of Physics.

General information

State: Published
Organisations: School of Physics and Astronomy
Authors: Gomez Iglesias, A., Fenn, J. G., Mazilu, M., Miller, A.
Keywords:  (DEMULTIPLEXER, RATES)
Number of pages: 3
Pages: 121108
Publication date: 19 Sep 2005
Peer-reviewed: Yes

Publication information

Journal: Applied Physics Letters
Volume: 87
Issue number: 12
ISSN (Print): 0003-6951
Original language: English
Source: WOS
Source-ID: 000231907200008

Research output: Contribution to journalArticle

Dual lattice photonic-crystal beam splitters

Light propagation in photonic crystals (PhC) is both sensitive to incident angle and wavelength. By combining two different PhC lattices, we utilize this effect to demonstrate a wavelength-dependent beam splitter with enhanced angular separation. The first lattice acts as a superprism that separates the incoming light according to wavelength, whereas the second lattice acts as an angular amplifier. We obtain 90 degrees angular separation for two wavelengths separated by 70 nm (1300 nm regime) in a structure that is less than 10 mu m long. (c) 2005 American Institute of Physics.

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews, Microphotonics and Photonic Crystals Group
Authors: Wu, L. J., Mazilu, M., Gallet, J. F., Krauss, T. F.
Keywords:  (SUPERPRISM PHENOMENA)
Number of pages: 3
Publication date: 23 May 2005
Peer-reviewed: Yes

Publication information

Journal: Applied Physics Letters
Volume: 86
ISSN (Print): 0003-6951
Original language: English
Source: WOS
Source-ID: 000229544200006

Research output: Contribution to journalArticle

1.13. 2003

Low-threshold, multi-gigahertz repetition-rate femtosecond Ti : sapphire laser

A repetition rate of 2.3 GHz is achieved in a femtosecond Ti:sapphire laser. Pulses of 240 fs duration centred on 840 nm are produced from a simple 4-mirror laser cavity that incorporates a saturable Bragg reflector and operates at pump powers as low as 400 mW.

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews
Authors: Stormont, B., Cormack, I. G., Mazilu, M., Brown, C. T. A., Burns, D., Sibbett, W.
Number of pages: 3
Pages: 1820-1822
Publication date: 11 Dec 2003
Peer-reviewed: Yes

Publication information

Journal: Electronics Letters
Volume: 39
ISSN (Print): 0013-5194
Original language: English
Source: WOS
Source-ID: 000187990500034

Research output: Contribution to journalArticle

Beam steering in planar-photonic crystals: From superprism to supercollimator

We utilize the anomalous dispersion of planar-photonic crystals (PhCs) near the dielectric band edge to control the wavelength-dependent propagation of light. Light beams with up to 20degrees divergence were collimated over a 25-nm (1285 nm to 1310 nm) bandwidth using a triangular lattice. The "super-prism" phenomenon is demonstrated in the same configuration, simply by tuning the wavelength. Sources of loss are discussed. Both the plane-wave expansion calculation and finite-difference time-domain simulation match well with the experimental results. This is the first experimental demonstration of self-collimating phenomena in a PhC configuration.

General information

State: Published
Organisations: School of Physics and Astronomy, The University of St Andrews, Microphotonics and Photonic Crystals Group
Authors: Wu, L. J., Mazilu, M., Krauss, T. F.
Keywords:  (angular dispersion, loss, planar-photonic crystals, self-collimating phenomena)
Number of pages: 6
Pages: 561-566
Publication date: Feb 2003
Peer-reviewed: Yes

Publication information

Journal: IEEE Journal of Lightwave Technology
Volume: 21
Issue number: 2
Original language: English
Source: WOS
Source-ID: 000182374900029

Research output: Contribution to journalArticle

1. Research output