From the abstract: We propose and demonstrate a novel high numerical aperture (NA) focusing
system composed of an annular beam with alternate radially and
azimuthally polarized rings, focused by a devil’s lens (DL), and further
investigate its radiation forces acting upon a Rayleigh particle both
analytically and numerically. Strongly focused cylindrical vector beams
produce either dark-centered or peak-centered intensity distributions
depending on the state of polarization, whereas the DL produces a series
of foci along the propagation direction. We exploit these focusing
properties and show that by selecting an appropriate truncation
parameter in front of the focusing lens, the proposed optical focusing
system can selectively trap and manipulate dielectric micro-particles
with low or high refractive indices by simply adjusting the radius of
the pupil or the beam. Finally, the stability conditions for effectively
trapping and manipulating Rayleigh particles are analyzed. The results
obtained in this work are of interest in possible applications in
optical confinement and manipulation, sorting micro-particles, and
making use of a DL.
Friday 2 December 2016
Paper published in JOSA A
Our paper on the optical trapping forces of a poarization-structured beam focused by a fractal (Devil's) lens has been published as Zhirong Liu and P. H. Jones, 'Radiation forces acting upon a
Rayleigh particle by highly focused alternate radially- and
azimuthally-polarized beams modulated by a Devil's Lens', Journal of the Optical Society of America A 33 2501-2508 (2016).
From the abstract: We propose and demonstrate a novel high numerical aperture (NA) focusing
system composed of an annular beam with alternate radially and
azimuthally polarized rings, focused by a devil’s lens (DL), and further
investigate its radiation forces acting upon a Rayleigh particle both
analytically and numerically. Strongly focused cylindrical vector beams
produce either dark-centered or peak-centered intensity distributions
depending on the state of polarization, whereas the DL produces a series
of foci along the propagation direction. We exploit these focusing
properties and show that by selecting an appropriate truncation
parameter in front of the focusing lens, the proposed optical focusing
system can selectively trap and manipulate dielectric micro-particles
with low or high refractive indices by simply adjusting the radius of
the pupil or the beam. Finally, the stability conditions for effectively
trapping and manipulating Rayleigh particles are analyzed. The results
obtained in this work are of interest in possible applications in
optical confinement and manipulation, sorting micro-particles, and
making use of a DL.
From the abstract: We propose and demonstrate a novel high numerical aperture (NA) focusing
system composed of an annular beam with alternate radially and
azimuthally polarized rings, focused by a devil’s lens (DL), and further
investigate its radiation forces acting upon a Rayleigh particle both
analytically and numerically. Strongly focused cylindrical vector beams
produce either dark-centered or peak-centered intensity distributions
depending on the state of polarization, whereas the DL produces a series
of foci along the propagation direction. We exploit these focusing
properties and show that by selecting an appropriate truncation
parameter in front of the focusing lens, the proposed optical focusing
system can selectively trap and manipulate dielectric micro-particles
with low or high refractive indices by simply adjusting the radius of
the pupil or the beam. Finally, the stability conditions for effectively
trapping and manipulating Rayleigh particles are analyzed. The results
obtained in this work are of interest in possible applications in
optical confinement and manipulation, sorting micro-particles, and
making use of a DL.
Wednesday 2 November 2016
Paper published in Optics Letters
Our paper on optical binding in two-dimensions has been published as Xiang
Han, Hui Luo, Guangzong Xiao and P. H. Jones. 'Optically bound colloidal lattices in evanescent optical fields', Optics Letters 41 4935 (2016).
From the abstract: In this Letter, we demonstrate the formation of a stable two-dimensional
lattice of colloidal particles in the interference pattern formed by
four evanescent optical fields at a dielectric interface. The
microspheres are observed to form a two-dimensional square lattice with
lattice vectors inclined relative to the beam propagation directions. We
use digital video microscopy and particle tracking to measure the
Brownian motion of particles bound in the lattice, and use this to
characterize fluctuations in the local ordering of particles using the
bond orientational order parameter, the probability distribution of
which is shown to be a chi-squared distribution. An explanation for the
form of this distribution is presented in terms of fluctuations of the
modes of a ring of particles connected by springs.
From the abstract: In this Letter, we demonstrate the formation of a stable two-dimensional
lattice of colloidal particles in the interference pattern formed by
four evanescent optical fields at a dielectric interface. The
microspheres are observed to form a two-dimensional square lattice with
lattice vectors inclined relative to the beam propagation directions. We
use digital video microscopy and particle tracking to measure the
Brownian motion of particles bound in the lattice, and use this to
characterize fluctuations in the local ordering of particles using the
bond orientational order parameter, the probability distribution of
which is shown to be a chi-squared distribution. An explanation for the
form of this distribution is presented in terms of fluctuations of the
modes of a ring of particles connected by springs.
Tuesday 11 October 2016
PhD project in Advanced Characterisation of Materials CDT
The UCL-Imperial CDT in Advanced Characterisation of Materials is now accepting applications. You can apply for a project in the UCL Optical Tweezers Group in collaboration with Valeria Garbin's Group in the Department of Chemical Engineering at Imperial on Nanomechanical Characterisation of Soft Materials.
Project abstract:
The project objective is to develop a suite of analytical techniques, including optical tweezers and microfluidics, for characterising the (nano)mechanical properties of ‘soft’ materials such as liposomes or biomembranes. The principal aims of this project are:
(i) to study the mechanical properties of biomimetic vesicles undergoing extreme deformations as a result of an applied external stress, e.g. optical, acoustic, or fluid shear forces;
(ii) to study phase separation and rupture in artificial vesicles under external forcing;
(iii) to use the result of the above studies to engineer membrane materials with properties optimised for applications including controlled drug release and microreactors.
During the project the student will acquire skills in microfluidics, microdevice fabrication, optics, modelling (including light scattering and transport phenomena), image analysis, and (micro)rheology.
Contact Phil Jones or Valeria Garbin for details
Project abstract:
The project objective is to develop a suite of analytical techniques, including optical tweezers and microfluidics, for characterising the (nano)mechanical properties of ‘soft’ materials such as liposomes or biomembranes. The principal aims of this project are:
(i) to study the mechanical properties of biomimetic vesicles undergoing extreme deformations as a result of an applied external stress, e.g. optical, acoustic, or fluid shear forces;
(ii) to study phase separation and rupture in artificial vesicles under external forcing;
(iii) to use the result of the above studies to engineer membrane materials with properties optimised for applications including controlled drug release and microreactors.
During the project the student will acquire skills in microfluidics, microdevice fabrication, optics, modelling (including light scattering and transport phenomena), image analysis, and (micro)rheology.
Contact Phil Jones or Valeria Garbin for details
Friday 5 August 2016
Postdoc position in UCL Optical Tweezer Group
The Optical Tweezers group at UCL (www.ucl.ac.uk/~ucapphj) is looking to recruit a postdoctoral research associate to work on the British Council-funded project “Manipulation and Destruction of Cancer Cells Using Cavitation Bubbles by Optical and Acoustic Tweezers”.
The aim of the project is to use optical and acoustic techniques to manipulate microscopic bubbles in the vicinity of cancer cells, with the goal of destroying them either by enhancement of drug uptake, or by physical disruption of the cell membrane.
The project will involve several research visits to our collaborators Dr Burcin Unlu (Bogazici University, Istanbul) and Dr Giovanni Volpe (Bilkent University, Ankara).
This position is funded for 18 months in the first instance.
The successful candidate should have (or be about to obtain) and PhD in Physics or Medical Physics, and expertise in experimental optics and/or acoustics (including photoacoustics).
Please contact Dr Phil Jones for further detail, or see jobs.ac.uk to apply.
The closing date for applications is 26 August 2016.
The aim of the project is to use optical and acoustic techniques to manipulate microscopic bubbles in the vicinity of cancer cells, with the goal of destroying them either by enhancement of drug uptake, or by physical disruption of the cell membrane.
The project will involve several research visits to our collaborators Dr Burcin Unlu (Bogazici University, Istanbul) and Dr Giovanni Volpe (Bilkent University, Ankara).
This position is funded for 18 months in the first instance.
The successful candidate should have (or be about to obtain) and PhD in Physics or Medical Physics, and expertise in experimental optics and/or acoustics (including photoacoustics).
Please contact Dr Phil Jones for further detail, or see jobs.ac.uk to apply.
The closing date for applications is 26 August 2016.
Wednesday 27 July 2016
Paper published in Nano Letters
Our paper on the dynamics of silison nanowires in optical tweezers has been published as A. Irrera et al, 'Photonic torque microscopy of the non-conservative force field for optically trapped silicon nanowires', Nano Letters 16, 4181-4188 (2016).
From the abstract: We measure, by photonic torque microscopy, the nonconservative
rotational motion arising from the transverse components of the
radiation pressure on optically trapped, ultrathin silicon nanowires.
Unlike spherical particles, we find that nonconservative effects have a
significant influence on the nanowire dynamics in the trap. We show that
the extreme shape of the trapped nanowires yields a transverse
component of the radiation pressure that results in an orbital rotation
of the nanowire about the trap axis. We study the resulting motion as a
function of optical power and nanowire length, discussing its
size-scaling behavior. These shape-dependent nonconservative effects
have implications for optical force calibration and optomechanics with
levitated nonspherical particles.
Monday 4 April 2016
Paper published in Scientific Reports
Our work on assessing the chage in deformability of red blood cells from patients with the condition diabetic retinopathy has been published as R. Agrawal et al. 'Assessment
of red blood cell deformability in type 2 diabetes mellitus and
diabetic retinopathy by dual optical tweezers stretching technique', Scientific Reports 6 15873, doi:10.1038/srep15873 (2016).
The movie below shows a red blood cell being stretched using our optical tweezers.
Tuesday 15 March 2016
Optical Tweezers: Principles & Applications
Combining state-of-the-art research with a strong pedagogic approach, this text provides a detailed and complete guide to the theory, practice and applications of optical tweezers. In-depth derivation of the theory of optical trapping and numerical modelling of optical forces are supported by a complete step-by-step design and construction guide for building optical tweezers, with detailed tutorials on collecting and analysing data. Also included are comprehensive reviews of optical tweezers research in fields ranging from cell biology to quantum physics. Featuring numerous exercises and problems throughout, this is an ideal self-contained learning package for advanced lecture and laboratory courses, and an invaluable guide to practitioners wanting to enter the field of optical manipulation. The text is supplemented by www.opticaltweezers.org, a forum for discussion and a source of additional material including free-to-download, customisable research-grade software (OTS) for calculation of optical forces, digital video microscopy, optical tweezers calibration and holographic optical tweezers.
"...it is quite simply excellent..." (M Padgett)
"...an amazing Optical Tweezers Software toolbox..." (J J Saenz)
"...a must for all Ph.D. students, researchers, and engineers [...] dealing with optical tweezers..." (M I Mishchenko)
Dr Zhirong Liu joins the group
Tuesday 19 January 2016
LCN / Physics / School of Pharmacy "Meet & Greet"
The department of Physics and Astronomy (P&A), the London Centre for Nanotechnology (LCN), and the School of Pharmacy (SOP) have organised a "meet and greet" event to facilitate links between physics / nanotechnology research on one hand, and pharmaceutical research on the other. The main aim of this event is to highlight respective research activities, expertise and facilities, and identify potential for cross-departmental collaborations and funding applications. This will be achieved by a series of short presentations on research questions, expertise, facilities and industrial collaborations, and by ample opportunity to chat over coffee/tea and lunch.
The event is open for UCL academics, postdocs and PhD students working in relevant or potentially relevant areas.
Wednesday 20th January 2016, 10:00am - 3:30pm
LMCB seminar room, UCL Laboratory for Molecular Cell Biology (map)
Programme:
10.00 – 10.15 Welcome and coffee
10.15 – 10.30 Introduction to the morning, with Simon Gaisford (SOP, morning chair), Jon Butterworth (P&A, Head of Department), Andrew Fisher (LCN, Director)
10.30 – 12:00 Short presentations (15min each)
- Soma Somavarapu (SOP)
- Andela Saric (P&A)
- Sudax Murdan (SOP)
- Bart Hoogenboom (LCN / P&A)
- TBC (SOP)
- Thanh Nguyen (LCN/ P&A)
12.00 – 1.00 Networking lunch
1.00 – 1.15 Introduction to the afternoon, with Bart Hoogenboom (LCN/P&A, afternoon chair) and Duncan Craig (SOP, Director)
1.15 – 2.45 Short presentations (15min each)
- Duncan Craig (SOP)
- Jochen Blumberger (LCN/P&A)
- Simon Gaisford (SOP)
- Phil Jones (P&A)
- Gareth Williams (SOP)
- David Bowler (LCN/ P&A)
2.45 – 3:30 Wrap up followed by coffee/tea
The event is open for UCL academics, postdocs and PhD students working in relevant or potentially relevant areas.
Wednesday 20th January 2016, 10:00am - 3:30pm
LMCB seminar room, UCL Laboratory for Molecular Cell Biology (map)
Programme:
10.00 – 10.15 Welcome and coffee
10.15 – 10.30 Introduction to the morning, with Simon Gaisford (SOP, morning chair), Jon Butterworth (P&A, Head of Department), Andrew Fisher (LCN, Director)
10.30 – 12:00 Short presentations (15min each)
- Soma Somavarapu (SOP)
- Andela Saric (P&A)
- Sudax Murdan (SOP)
- Bart Hoogenboom (LCN / P&A)
- TBC (SOP)
- Thanh Nguyen (LCN/ P&A)
12.00 – 1.00 Networking lunch
1.00 – 1.15 Introduction to the afternoon, with Bart Hoogenboom (LCN/P&A, afternoon chair) and Duncan Craig (SOP, Director)
1.15 – 2.45 Short presentations (15min each)
- Duncan Craig (SOP)
- Jochen Blumberger (LCN/P&A)
- Simon Gaisford (SOP)
- Phil Jones (P&A)
- Gareth Williams (SOP)
- David Bowler (LCN/ P&A)
2.45 – 3:30 Wrap up followed by coffee/tea
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