Rayleigh scattering correlation microspectroscopy is developed and applied to study diffusion dynamics of some
nanospheres in water. It was clearly found that the diffusion constant of gold nanoparticles decreased with increasing
excitation laser power at the excitation wavelength of higher absorption cross section. This behavior was explained in
terms of a coupling between laser trapping by the scattering excitation laser itself and laser heating of the particle. In the
case of non-absorbing nanospheres such as silica and polystyrene, the excitation power dependence can be ascribed only
to the laser trapping. Experimental setup is introduced, theoretical formulation is described, and future development of this measurement is considered.
We present direct observation of particle transfer and assembling upon laser irradiation under a microscope. We
employed gold nanoparticles (60 nm) dispersed in water as optical markers and studied laser trapping and accompanying
phenomenon by wide-field Rayleigh scattering microscopy. At the focal spot of the near IR laser, laser trapping of gold
was observed. Simultaneously, we observed that the particle migration toward the focal spot from all the directions
within several tens micrometer. We consider that thermocapillary effect due to laser heating can assist the particle
migration from far away, resulting in concentration increase not only at the focal point but also near the surrounding area.
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