Expertise and knowledge
I have long-time experience in optics and plasma physics. I was involved in plasma physics computer simulations, experimental plasma diagnostic techniques (Langmuir probe, mass spectroscopy, etc) and plasma deposition techniques. In the period July 2007-May 2012 I participated in the further development of optical micromanipulation techniques at the position of postdoctoral fellow. I was fully responsible for experimental and theoretical research related to optical force interaction in counter-propagating trapping beams with tailored intensity profiles. My expertises in this area cover optical design of the set-ups, determination of aberrations and parameters in focused beams, measurement of optical forces and trapping potentials, CCD image processing, simulation of optical forces, design of trapping and microfluidic cells, handling and optical manipulation with droplets in immiscible fluids and air.
Complex rotational dynamics of multiple spheroidal particles in a circularly polarized, dual beam trap
We examine the rotational dynamics of spheroidal particles in an optical trap comprising counter-propagating Gaussian beams of opposing helicity. Isolated spheroids undergo continuous rotation with frequencies determined by their size and aspect ratio, whilst pairs of spheroids display phase locking behaviour. The introduction of additional particles leads to yet more complex behaviour. Experimental results are supported by numerical calculations. more.
Optical traping of plasmon nanoparticles
It was previously believed that larger metal nanoparticles behave as tiny mirrors that are pushed by the light beam radiative force along the direction of beam propagation, without a chance to be confined. However, several groups have recently reported successful optical trapping of gold and silver particles as large as 250 nm. We offer a possible explanation based on the fact that metal nanoparticles naturally occur in various non-spherical shapes and their optical properties differ significantly due to changes in localized plasmon excitation. We demonstrate experimentally and support theoretically three-dimensional confinement of large gold nanoparticles in an optical trap based on very low numerical aperture optics. We showed theoretically that the unique properties of gold nanoprisms allow an increase of trapping force by an order of magnitude at certain aspect ratios. These results pave the way to spatial manipulation of plasmonic nanoparticles using an optical fibre, with interesting applications in biology and medicine. more.
Following the Keplerian idea of optical forces, one would intuitively expect that an object illuminated by sunlight radiation or a laser beam will be accelerated along the direction of photon flow. Recent theoretical studies have shown that small particles can be pulled by light beams against the photon stream, even in beams with uniform optical intensity along the propagation axis. Here, we present a geometry to generate such a ‘tractor beam’, and experimentally demonstrate its functionality using spherical microparticles of various sizes, as well as its enhancement with optically self-arranged structures of microparticles. In addition to the pulling of the particles, we also demonstrate that their two-dimensional motion and one-dimensional sorting may be controlled conveniently by rotation of the polarization of the linearly polarized incident beam. The relative simplicity of this geometry could serve to encourage its widespread application, and ongoing investigations will broaden the understanding of the light–matter interaction through studies combining more interacting micro-objects with various properties. more
The light-matter interaction is behind the key processes in the nature or society, e.g. photosynthesis, vision, earth heating, air circulation, transfer and storage of information. However these examples employ only the photon energy. Except the energy photons also carry a linear or angular momentum and its transfer to matter during photon scattering leads to mechanical interaction of light upon a matter. Except tightly focused beams used in optical tweezers other geometries were developed, too. They use elongated or wider beams that illuminate more objects at the same time. Mutual scattering of the trapping beam by the objects mediate new type of long-range interaction between these objects - optical binding. It leads to the spontaneous self-arrangement of micro-particles into stable formations with well defined inter-particle distances - optically bound matter more.
Optical trapping in the Air
The goal of this fully basic research oriented project is to develop optical trapping and manipulation of solid particles and liquid droplets in the air. The geometry of two counter-propagating trapping beams is adapted to enable fast reconfiguration of the trapping beams via a computer interface, fast observation of the trapped particles to measure the trap properties and to quantify collective behaviour of more confined particles interacting via scattered light (optical binding). Since the widely used theoretical models dealing with the behaviour of optically trapped particles consider simplified over-damped case (particle is placed in liquid and the inertial term in Langevine equation is neglected), our experimentally achieved results will serve as the starting point for subsequent comparison and refinement of theoretical models. more
Optical trapping in RF plasma
A dusty plasmas have shown to be an ideal system for investigation of strongly coupled systems. Microscopic particles charged up (due to the fluxes of electrons and ions) in plasma to the floating potential similar to floating Langmuir probes. In typical laboratory experiments in parallel-plate rf discharge the so-called plasma sheaths are formed near the electrodes. The negatively charged dusty particles are confined in the planes parallel to lower electrodes, where the gravitational force is balanced with electric force (negative charge is repelled from the electrodes). Thank to the Coulomb interaction between the particles they form so-called Coulomb crystal. Laser beam has been used to study phase transition, defect dynamics, waves, Mach cones, etc. in such crystal. The dusty particles can also be used as very tiny plasma diagnostic tool. The optical manipulation techniques offer very attractive possibility how to use the dusty particle for plasma diagnostic purpose due to their non-contact character.
Computer simulation of low temperature plasma
A fully kinetic particle model was used for simulation of RF glow discharge (used in various stages of micro-electronic manufacturing). The model was based on well-known Monte Carlo and particle in cell methods. Various interesting problems were investigated, e.g. role of secondary electrons created on electrodes, a mirror effect observed at plasma-chemical deposition and sputtering reactor, an influence of the Ramsauer minimum on plasma characteristics.
An afterglow plasma in FALP (Flowing Afterglow Langmuir Probe) apparatus was studied in the second part of the thesis. Attachment and detachment of electrons to molecule C6F5X (X = Cl, I) were studied in the FALP apparatus. First the problem was studied using simple dimensionless model, which is often used in this experiment. Then one-dimensional simulation model which solved diffusion equation and Poisson equation was developed. Both models were compared and the validity of the dimensionless model was discussed more.
University St Andrews
Kishan Dolakia at School of Physics
University of Dundee
Tomas Cizmar at School of Engineering, Physics and Mathematics
Christian-Albrechts University in Kiel
Holger Kersten at Institut für Experimentelle und Angewandte Physik
H. Daniel Ou-Yang at Soft Matter & Biophotonics Laboratory
David Trunec at Department of Physical Electronics