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▲ [11a-PA1-5] Laser trapping of 20 μm polystyrene particles at solution surface leading to necklace-like pattern of 1 μm particles
Keywords:Colloidal particle, Optical scattering
We are studying intensively on “Optically Evolved Assembly Formation in Laser Trapping” of molecules, nanoparticles (NPs) and microparticles (MPs) where optical potential expands from the focus to the outside of a few ten micrometer through scattering and propagation of the trapping laser [1-2]. For polystyrene (PS) MPs of 1 μm at solution surface, a large single assembly of NPs is formed, undergoes structured transformation, and ejects some NPs as a linearly aligned manner. Here we report a new behavior of 20 μm PS MPs and 1 μm PS MPs mixture solution at air/solution, showing necklace formation of small particles on the big particle.
Upon 1064 nm CW laser irradiation, a few 20 μm PS MPs rapidly trapped at the focus and a necklace-like pattern of 1 μm PS MPs was formed on the top of the central irradiated MP (Fig. 1). Sequentially, the strong scattering light was observed in surrounding area, and with continued irradiation the necklace-like pattern appeared on other surrounding MPs. The patterns disappear upon turning off the laser, but quickly return back when the laser was switched on again. Very strong scattering light form the center to outer MPs was observed in the scattering image, and radial scattering from the surface of MPs was detected in transmission images. We consider that the necklace formation is made possible due to the propagation of scattering light where capillary force induced by surface deformation probably contributes [3].
Upon 1064 nm CW laser irradiation, a few 20 μm PS MPs rapidly trapped at the focus and a necklace-like pattern of 1 μm PS MPs was formed on the top of the central irradiated MP (Fig. 1). Sequentially, the strong scattering light was observed in surrounding area, and with continued irradiation the necklace-like pattern appeared on other surrounding MPs. The patterns disappear upon turning off the laser, but quickly return back when the laser was switched on again. Very strong scattering light form the center to outer MPs was observed in the scattering image, and radial scattering from the surface of MPs was detected in transmission images. We consider that the necklace formation is made possible due to the propagation of scattering light where capillary force induced by surface deformation probably contributes [3].