Optical binding presents an original method for self- arrangement of solid microparticles in liquid or air. The
resulting equilibrium positions of the particles in an optically bound structure (OBS) are not only influenced
by the spatial intensity profiles of the incident laser beams but also by the light scattered from all the bound
particles. The inter-particle distances in OBSs can be externally modified by changing the refractive index of
the medium or the spatial intensity distribution of the beams. Especially the last option is now well developed
due to the technology of spatial light modulators (SLM). We utilized this tool to generate OBSs in counterpropagating
laser beams having various spatial intensity profiles. In contrast to the previous methods, where
OBSs were kept stationary without dynamic control, we modified dynamically the optical cage for self-arranged
particles which led to enlargement or shrinking of the OBS. Using elaborate optical fields suitable for particular
cases we demonstrated the size tunability of OBSs that were self-arranged along one, two or three dimensions.
Compressing of the optical cage below a certain limit led to a collapse of the self-arranged micro-structures,
thus indicating a phase transitions in such colloidal structures. Within a system of counter-propagating optical
vortices we observed transfer of angular momentum of light to two-dimensional OBSs, revolving around the
intrinsic on-axis phase singularity of the trapping beams.
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Oto Brzobohatý ; Vítězslav Karásek ; Martin Šiler and Pavel Zemánek
Dynamic size tuning of multidimensional optically bound matter
", Proc. SPIE 8697, 18th Czech-Polish-Slovak Optical Conference on Wave and Quantum Aspects of Contemporary Optics, 86970U (December 18, 2012); doi:10.1117/12.2001101; http://dx.doi.org/10.1117/12.2001101