Laser trapping of nanoparticles
We recently introduced a new technique of trapping nanoparticles in air using optical vortices. The technique is based upon thermal forces induced by uneven heating of light absorbing particles with a laser beam. The laser vortices with doughnut-shaped intensity profile provide a means to trap particles and push them along the zero-intensity beam axis to a desirable location. Our studies cover optical trapping, guiding, and pin-point positioning of particles in air, as well as simultaneous trapping thousands of particle with a single laser beam. Optical vortices can be applied to touch-free transport of containers holding gases, ultra-pure or dangerous substances, and biological macromolecules.
Laser trapping and agglomerating nanoparticles can be applied for monitoring and removal of nano-pollutants from air, offering a new avenue toward environmental protection in the workplace of the nanotechnology industry. We apply this approach to photophoretic traps in air, and investigate the dependence of trap stiffness on laser power, polarization state, and gas pressure.
We analyse the equilibrium positions of trapped spheres depending on laser power and polarisation. This effect, brought about by the balancing of weight and trapping force, could in principle be used to weigh single particles with masses ranging from picograms to 100s of nanograms. Analysis of a particle's motion can recover information about the particle, the trapping forces and the medium in which the particle is trapped.
Figure: Trapping particles with the bottle beam. (a) The bottle beam trapping experiment. The inset shows the trapped particles. Red arrow indicates the HeNe beam. Carbon nanoparticles (red) inside the optical bottle. Opposite side views of the 3-D intensity distribution near the first (top) and seventh (bottom) axial intensity minimum. Side views of a secondary bottle corresponding to the axial intensity minimum (bottom). Arrows indicates beam direction.
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- Li Li, Woei Ming Lee, Xiangsheng Xie, Wieslaw Krolikowski, Andrei V. Rode and Jianying Zhou, “Shaping Self-imaging Bottle Beams with Modified Quasi-Bessel Beams”, Optics Letters 39, 2278-2281 (2014)
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- V. G. Shvedov, A. V. Rode, Ya. V. Izdebskaya, D. Leykam, A. S. Desyatnikov, W. Krolikowski, and Yu. S. Kivshar, “Laser speckle field as a multiple particle trap” Journal of Optics 12, 124003 (2010)
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