New Group Members

This year we welcome two final year undergraduate students into the Optical Tweezers Group for their MSci projects.  Chris Richards will be working on light scattering calculations relevant to our optical trapping and optical binding experiments.  Zhi Wong will be investigating the optical and light scattering properties of metallic nanoparticles in his project on Plasmonics.

SPIE Optics + Photonics Conference

Marios and Susan are attending the Optical Trapping and Optical Micromanipulation IX conference, part of SPIE Optics + Photonics, in San Diego, CA, 12 - 16 August.  Susan will be giving a talk 'Optical squeezing of microbubbles: Ray optics and Mie scattering calculations' (Paper 8458-51) on Wed 16 Aug (Session 10: Combining optical traps with acoustics) and presenting a poster on 'Shaping of the trapping volume in optical tweezers using cylindrical vector beams' (Paper 8458-110).  Marios will be presenting a poster 'Optically bound particle structures in evanescent wave traps' (Paper 8458-124).

Paper published in Optics Letters

Our paper 'Optical trapping of single walled carbon nanotubes with cylindrical vector beams has been published as M. G. Donato et al, Opt. Lett. 37 3381-3383 (2012).  

From the abstract: We use laser beams with radial and azimuthal polarization to optically trap carbon nanotubes. We measure force constants and trap parameters as a function of power showing improved axial trapping efficiency with respect to linearly polarized beams. The analysis of the thermal fluctuations highlights a significant change in the optical trapping potential when using cylindrical vector beams. This enables the use of polarization states to shape optical traps according to the particle geometry, as well as paving the way to nanoprobe-based photonic force microscopy with increased performance compared to a standard linearly polarized configuration.

This paper has also been selected for inclusion in the Virtual Journal of Biomedical Optics 7 (2012)

Royal Society Summer Exhibition

This week we have been at the Royal Society Summer Exhibition 2012 with a display titled POP! The sound of bubbles.  Opposite you can see members of the team explaining the science of bubbles to guests at the soiree on Thu 05 Jul.

The exhibition and our display also featured on the BBC news, and in BBC R4's Material World programme on 05 July. The podcast of this show will be available to download for the next few weeks. 

Trapping and deformation of microbubbles in a dual-beam fibre-optic trap

  

Our paper Trapping and deformation of microbubbles in a dual-beam fibre-optic trap has been published as S E Skelton et al, Journal of Optics 14 075706 (2012).

From the abstract:  We present results of numerical calculations to evaluate the performance of a dual-beam fibre-optic trap for low refractive index particles such as ultrasound contrast agent microbubbles. Using a geometrical optics approach, we determine the range of parameters of microbubble size and beam dimensions over which the optical trap is stable and evaluate the trapping forces and spring constants. Additionally, we calculate the optically induced stress profile over the surface of the microbubble and evaluate the resulting deformation of the microbubble using elastic membrane theory. Our results suggest that such an experiment could be a useful tool for quantifying the mechanical properties (elastic modulus) of the shell material of an ultrasound contrast agent microbubble.

This paper has been included in the IoPscience collection of featured articles "chosen for their quality and recency".

Fluctuations in Dynamical Systems Far From Equilibrium

The workshop will bring together people from applied mathematics, dynamical systems, condensed matter physics and statistical physics. The theme are fluctuations far from equilibrium, particularly in stochastic dynamics. A focus will be on so-called fluctuation relations, which generalize the second law of thermodynamics to small systems. They have been found to be generally valid very far from equilibrium. This active, recent topic of research will be discussed both from a theoretical and from an experimental point of view. Cross-links to large deviation theory and to anomalous stochastic processes will be explored.

Programme

11.30 - 12.30 Ian Ford, UCL: A rough guide to fluctuation relations

14.00 - 15.00 David Carberry, University of Bristol: Fluctuation Relations: Experimental Demonstrations

15.00 - 16.00 Adrian Baule, QMUL: Exact relations in non-equilibrium statistical mechanics

16.30 - 17.30  Nicholas Watkins, Cambridge, UK: Anomalous Diffusion, Anomalous Time Series, and the models that describe them

All talks will be held in seminar room M103 (first floor) of the Department of Mathematics at Queen Mary University of London.

For more information contact Prof Ferruccio Renzoni

Paper in Journal of Quantitative Spectroscopy and Radiative Transfer

Our paper Evanescent wave optical trapping and transport of micro- and nanoparticles on tapered optical fibers has been published online in the Journal of Quantitative Spectrocopy and Radiative Transfer doi: 10.1016/j.jqsrt.2012.06.005.

From the abstract: We investigate the manipulation of microscopic and nanoscopic particles using the evanescent optical field surrounding an optical fiber that is tapered to a micron-scale diameter, and propose that this scheme could be used to discriminate between, and thereby sort, metallic nanoparticles. First we show experimentally the concept of the transport of micron-sized spheres along a tapered fiber and measure the particle velocity. Having demonstrated the principle we then consider theoretically the application to the optical trapping and guiding of metallic nanoparticles, where the presence of a plasmon resonance is used to enhance optical forces. We show that the dynamics of the nanoparticles trapped by the evanescent field can be controlled by the state of polarization of the fiber mode, and by using more than one wavelength differently detuned from the nanoparticle plasmon resonance. Such a scheme could potentially be used for selectively trapping and transporting nano- or microscopic material from a polydisperse suspension.