CW laser trapping assembling of polystyrene nanoparticles at solution/air surface and solution/glass interface receives much attention as new methods to form nano-colloid crystals and to form molecular crystals. Focusing intense CW 1064 nm laser into a 1 micrometer-sized spot at solution surface of heavy water of polystyrene nanoparticles forms an assembly extending from the focus to about 10 micrometer. The disk-like assembly at the surface shows structural color, which was analyzed by transmission and Rayleigh light back scattering imaging and spectroscopy. Systematic spectral analysis reveals formation and decomposition dynamics of the crystal, its structural uniformity, its nanoparticle concentration dependence and so on. Why the trapping expands from the focus to the outside along the interface is considered in terms of inter-nanoparticle interactions, laser-induced heating/convection, surface energy, and so on. When this surface trapping method is applied to amino acids and organic molecules, their single crystals and assemblies are fabricated. Mostly one single crystal is prepared at the focal point upon laser irradiation, crystallization is made possible even in unsaturated solution, and crystal polymorph can be controlled by trapping laser polarization. The spatio-temporal controllability of laser trapping crystallization enables us to elucidate dynamics and mechanism of assembling and crystallization f nanoparticles.<br/><br/>Femtosecond laser trapping dynamics of nanoparticles in solution recently receives much attention, because trapping efficiency is enhanced and new behaviors never observed with CW laser are reported recently. In order to explain these results, we propose two new methods utilizing two femtosecond lasers. This gives new insight on “drag and relaxation” dynamics during and between pulses. These advances will be presented and considered in detail.

Laser trapping assembling and crystallization of nanoparticles at solution surface

251st National Meeting (2016)

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