Wednesday, 22 April 2015

Paper published in JOSA B

Our paper describing how to constuct an advanced optical tweezers experiment has been published as G. Pesce, G. Volpe, O. M. Maragò, P. H. Jones, S. Gigan, A. Sasso & G. Volpe.  'A step-by-step guide to the realisation of advanced optical tweezers', Journal of the Optical Society of America B 32 B84-B98 (2015).  This paper forms part of the joint Special Issue of Optics Express and JOSA B on Optical Cooling and Trapping organised by the OSA Technical Group.

From the abstract: Since the pioneering work of Arthur Ashkin, optical tweezers (OT) have become an indispensable tool for contactless manipulation of micro- and nanoparticles. Nowadays OT are employed in a myriad of applications demonstrating their importance. While the basic principle of OT is the use of a strongly focused laser beam to trap and manipulate particles, more complex experimental setups are required to perform novel and challenging experiments. With this article, we provide a detailed step-by-step guide for the construction of advanced optical manipulation systems. First, we explain how to build a single-beam OT on a homemade microscope and how to calibrate it. Improving on this design, we realize a holographic OT, which can manipulate independently multiple particles and generate more sophisticated wavefronts such as Laguerre–Gaussian beams. Finally, we explain how to implement a speckle OT, which permits one to employ random speckle light fields for deterministic optical manipulation.

Thursday, 26 March 2015

Paper published in Optics Express

Our paper on optical trapping using a beam with a wavefront shaped by a fractal-generated lens structure has been published as Jixiong Pu & P. H. Jones 'Devil's lens optical tweezers' Optics Express 23 8190-8199 (2015).  This paper forms part of the joint Special Issue of Optics Express and JOSA B on Optical Cooling and Trapping organised by the OSA Technical Group.

From the abstract: We demonstrate an optical tweezers using a laser beam on which is imprinted a focusing phase profile generated by a Devil’s staircase fractal structure (Cantor set). We show that a beam shaped in this way is capable of stably trapping a variety of micron- and submicron-sized particles and calibrate the optical trap as a function of the control parameters of the fractal structure, and explain the observed variation as arising from radiation pressure exerted by unfocused parts of the beam in the region of the optical trap. Experimental results are complemented by calculation of the structure of the focus in the regime of high numerical aperture.

Wednesday, 18 March 2015

SPIE Conference Proceedings: Photonics West

Proceedings from the SPIE Photonics West 2015 conference have been published.  These include our paper based on Phil's invited talk: P. H. Jones, C. J. Richards, T. J. Smart & D. Cubero.  'Dynamical stabilisation in optical tweezers', Proc SPIE 9379, Complex Light & Optical Forces IX, 93790L, doi: 10.1117/12.2078961, (2015)

From the abstract: We present a study of dynamical stabilisation of an overdamped, microscopic pendulum realised using optical tweezers. We first derive an analytical expression for the equilibrium dynamically stabilised pendulum position in a regime of high damping and high modulation frequency of the pendulum pivot. This model implies a threshold behavior for stabilisation to occur, and a continuous evolution of the angular position which, unlike the underdamped case, does not reach the fully inverted position. We then test the theoretical predictions using an optically trapped microparticle subject to fluid drag force, finding reasonable agreement with the threshold and equilibrium behavior at high modulation amplitude. Analytical theory and experiments are complemented by Brownian motion simulations.

Friday, 2 January 2015

MAPS Faculty Research Festival

The Faculty of Mathematical and Physical Sciences (MAPS) Research Festival will celebrate research activities across the faculty by highlighting notable achievements and ongoing projects from the eight departments.

The programme for the event is:

Prof. Ofer Lahav (MAPS Vice Dean for Research)  - "Welcome"
Prof. David Price (Vice Provost for Research)  - "UCL Research Strategy"
Prof. Nick Brook (MAPS Dean) - "MAPS Research Strategy"
Dr David Scanlon (Chemistry) - "Polymorph engineering of TiO2: Understanding the correlation between local coordination, absolute reference potentials and practical applications"
Prof. Rachel McKendry (LCN) - "Connecting for Global Health: nanosensors, mobile phones and big data"
Dr Timo Betcke (Mathematics) - "BEM++: Open-source software development in Mathematics"
Ms. Beate Franke (Statistics) - "Understanding network structure"
Dr Phil Jones (Physics and Astronomy) - "Current research in Biological Physics"
Prof. Dario Alfe (Earth Sciences) - "A window to the Earth's core"

Prof. Mat Page (MSSL) - "Discoveries with Swift"
Dr Jack Stilgoe (STS) - "Responsible Research and Innovation"

Tuesday, 14 October 2014

SPIE Conference Proceedings: OTOM XI

Proceedings from the SPIE Optics + Photonics 2014 conference have been published.  These include Chris F's paper on optical and acoustic manipulation of microbubbles in a microfluidic device: C. R. Fury, P. H. Jones and G. Memoli.  'Multi-scale manipulation of microbubbles employing simultaneous optical and acoustical trapping', Proc SPIE 9164, Optical Trapping and Optical Micromanipulation XI, 91642Z, doi: 10.1117/12.2061622 (2014).

From the abstract: We present a dual-modality microbubble trapping system that incorporates the fine spatial resolution of optical tweezers, with the long range, high force manipulation of acoustic tweezers, in a single microfluidic system. We demonstrate aggregation of polymer microbubbles in the node of an acoustic field, and subsequent selection and separation of a single microbubble using holographic optical tweezers. We further characterize the optical tweezers by measuring the transverse spring constant, and use the calibrated trap to determine the acoustic force on the bubble for varying parameters of optical trap diameter and power, and acoustic frequency and driving voltage. Further development of the system to include acoustic emission measurement is presented, with the goal of having a multi-purpose mechanical and cavitation detection set-up combined into a single system

Monday, 13 October 2014

New Group Members

Two new members have joined the Optical Tweezers Group at the start of the 2014-15 academic year.  Nick Tidy has joined us as a PhD student.  Nick studied Physics at Birmingham University and graduated in 2014.  He will be working with our collaborators at JAIST on optical trapping of polymer vesicles.  Stefan Siwiak-Jaszek is a fourth year undergraduate at UCL studying Natural Sciences.  Stefan spent the third year of his degree studying at the National University of Singapore, and has retured to UCL for his final year where he will be using optical tweezers to study stochastic thermodynamic processes for his MSci project.

Tuesday, 26 August 2014

Optics Express & JOSA B: Joint Special Issue on Optical Trapping

The OSA Technical Group on Optical Cooling and Trapping is organizing a joint special issue of the journals Optics Express and the Journal of the Optical Society of America B.  Topics for the special issues include, but are not limited to, the physics and application of laser cooling, electromagnetic trapping and other radiative manipulation of neutral atoms, ions, dielectric particles and nanostructures.  Subissions for the joint Special Issue will open on 01 November 2014 and close on 05 January 2015, with publication scheduled for early in 2015.  The Guest Editors for the Special Issue will be:

Antonio A. R. Neves (Federal University of ABC, Brazil)
Philip H. Jones (UCL, UK)
Onofrio M. Maragò (CNR-IPCF, Italy