Tuesday, 31 May 2011

New group members

Ewa Karczewska is joining the UCL Optical Tweezers Group today for an eight week research project funded by the Nuffield Foundation.  The foundation provides research bursaries for undergraduate students considering a career in research to gain experience in a research lab over the summer vacation.  The Optical Twezeers Group has peviously hosted three Nuffield bursary students: Muddassar Rashid (2008), Alex Dunning (2009) and Radhika Patel (2010).

Ewa is a second year undergraduate student at UCL, studying for an MSci degree in Physics.  She will be contributing to a number of different projects presently running in the group, and making regular updates of her progress on this blog.

Monday, 16 May 2011

Andrei Rode visit and seminar

This week Prof Andrei Rode from the Laser Physics Centre of the Australian National University, Canberra is visiting.  While here he will also be giving an AMOP Physics seminar on Optical vortices: Trapping of particles and material processing.

Abstract: In physics and biology, manipulation of microscopic objects achieved remarkable precision and functionality using very small radiation pressure of light and dipole-induced gradient forces, so called optical tweezers.  Stable trapping of absorbing particles in air was not achieved till now due to the dominance of forces from thermal interaction of the laser-irradiated particle with the molecules of ambient gas.  We address this challenge by developing a touch-free optical trapping of particles suspended in air with optical vortices.  The ability to guide absorbing particles along the vortex core in a stable and controlled manner can be employed further for high-accuracy manipulation of particles in three dimensions.
We also developed a femtosecond vortex beam converter where polarization singularities are created when the beam propagates through a birefringent crystal, to produce sub-micron ring structures on the surface of fused silica and glass samples. We employ this technique to generate optical vortex as well as radially (TM) and azimuthally (TE) polarized fs-laser pulses for sub-┬Ám structuring of glass samples.
Interaction of tightly focused multiple fs-pulses with transparent media allows one to imprint their local polarization pattern with sub-wavelength resolution, including the presence of the longitudinal component of electric field.  The materials’ response to the state of polarization of high intensity light fields has been used to map the complex vector structure in the focal volume of radially and azimuthally polarized fs-laser pulses.