Big Bang Science Fair

POP! The Sound of Bubbles was at the Big Bang Science Fair in the ExCeL Centre in Docklands 14 - 17 March.  Members of the NPL/UCL/Oxford microbubble project together with colleagues from NPL, Glasgow University and King's College demonstrated bubble science to over 63,000 visitors in four days.
Among the visitors to our stand was the Secretary of State for Business, Innovation and Skills, Vince Cable, here being shown our Kundt Tube demonstration of acoustic resonance by Ian Butterwoth of the NPL.

Susan Skelton PhD viva

Congratulations to Optical Tweezers PhD student Susan Skelton who has successfully defended her PhD thesis on Applications of cylindrical vector beams for optical micromanipulation.  Susan will be leaving the group to start a postdoc at the University of Osaka, Japan, in the Laboratory for Scientific Instrumentation and Engineering (LaSIE) under the supervision of Prof Satoshi Kawata.  Many thanks to Dr Stephen Hogan (UCL) and Dr David McGloin (Dundee University) for acting as examiners.

Well done Dr Skelton, and good luck in Japan!

AMOP Physics Open Day

On Wednesday 13 February the UCL AMOP Physics Group is holding an Open Day for students interested in studying for a PhD in the group.  The timetable for the day is:

13:00 - 13:30  Introductory talk by Dr Agapi Emmanouilidou and Prof Ferrucio Renzoni (A1)

13:30 - 13:45  Buffet Lunch (E7)

13:45 - 15:30 Poster presentations by research groups (E7)

14:00 - 16:00 Lab tours

A PhD studentship is available to work in the Optical Tweezers Group on the project Exploring stochastic thermodynamics with optical traps.

Simon Hanna visit and seminar

Simon Hanna (Bristol University) is visiting on Wed 30 Jan 2013 to give the AMOP Physics seminar.  Simon is a theoretician in the Nanophysics and Soft Matter Group at Bristol with wide-ranging interests including liquid crystals and polymer physics.  His talk, however, will be about modelling optical forces on specially shaped micoparticles in optical traps.

Title: Optimising forces and torques for optical micromanipulation, Simon Hanna (Bristol University)

Abstract: The motion of a colloidal particle in an optical field depends on a complex interplay between the structure of the field, and the geometry and composition of the particle. There are two complementary approaches to generating a particular force field. The first, involving sculpting of the optical field with e.g. a spatial light modulator, has been extensively developed.  A second method, highlighted recently, involves sculpting of the particles themselves, and has received much less attention. However, as modern two-photon polymerisation methods advance, this avenue becomes increasingly attractive for micromanipulation. In this talk I will show how computational methods may be used to optimise particle geometries in such a way as to produce desirable patterns of forces and torques.  These designs are then tested using particles fabricated using the two-photon method.  In particular, I will demonstrate the design of a constant force optical spring for use as a passive force clamp, a high efficiency optical wing, and a shape-optimised microtool.

Paper published in Optics Letters

Our paper 'Trapping volume control in optical tweezers using cylindrical vector beams' has been published as S. E. Skelton et al, Optics Letters 30 28-30 (2013).

From the abstract: We present the result of an investigation into the optical trapping of spherical microparticles using laser beams with a spatially inhomogeneous polarization direction [cylindrical vector beams (CVBs)]. We perform three-dimensional tracking of the Brownian fluctuations in the position of a trapped particle and extract the trap spring constants. We characterize the trap geometry by the aspect ratio of spring constants in the directions transverse and parallel to the beam propagation direction and evaluate this figure of merit as a function of polarization angle. We show that the additional degree of freedom present in CVBs allows us to control the optical trap strength and geometry by adjusting only the polarization of the trapping beam. Experimental results are compared with a theoretical model of optical trapping using CVBs derived from electromagnetic scattering theory in the T-matrix framework.

PhD Studentships Available

Two PhD studentships are available to work on a project funded by the Leverhulme Trust titled 'Exploring stochastic thermodynamics with optical traps', starting in 2013. The aim of this project is to use optical trapping experiments as a test-bed for fluctuation relations in non-equilibrium (driven) systems.

Project abstract: The theory of equilibrium statistical mechanics is well established, and has found direct or indirect confirmation in a wide range of experiments. This is not the case for the emerging field of non-equilibrium statistical mechanics. In this case, a general theory has yet to be formulated, although a number of theorems (e.g. fluctuation and work theorems) have been introduced to link different physical quantities in systems out of equilibrium. The aim of the proposed research is to develop further, through proof-of-principle experiments with optical traps, the foundations of non-equilibrium statistical mechanics, with a view towards a unified description. 

Studentships will pay a stipend and fees at the rate applicable for UK and European Union students only.

Contact Dr Phil Jones for further details

Pietro Cicuta visit and seminar

Pietro Cicuta (Cambridge University) is visiting the lab on Wednesday 07 November, and giving the AMOPP/BioP seminar.  Pietro works on a variety of problems relevant to soft matter and biological physics, including colloidal systems, complex fluids and membranes.  His talk is titled Emergence of collective states in active colloids, and the abstract is below:

Title: Emergence of collective states in active colloids. Pietro Cicuta (Cambridge University)

Abstract:  Coupled oscillators can, under some conditions, synchronise. There are examples of this everywhere in natural phenomena, technology, and material properties.  A relatively unexplored area is the synchronisation of colloidal oscillators: these are micron-sized objects, coupled through hydrodynamic interaction.   There is reason to study these because physiologically similar structures are thought to enable fluid transport in various organs;   technologically it might be possible to construct very sensitive micro-resonators.
Over the last few years we have worked in this area by developing an experimental platform: optical tweezers are used to create phase oscillators. This talk will present various strategies for making oscillators (active colloids), and the resulting collective behaviour of two or more of these elements.