Nonlinear effects in nanosuspensions by optical scattering force

This thesis presents the research on nonlinear optical effect in nanosuspensions. A continuous wave laser (wavelength at 532nm) is launched into a cuvette filled with a suspension of Polystyrene nanoparticles. Optical scattering force and viscosity will drive a flow in the nanoparticle suspension. The flow and the light beam can concentrate the nanoparticles and self-focus the laser beam. We use the He-Ne laser (wavelength at 632nm) to obtain the local refractive index change by interference. In order to understand the physical mechanism, we conduct several experiments. We launch the laser beam at different positions of the cuvette and observe the phenomena near the boundary when the flow symmetry is destroyed. We try to find better conditions for self-focusing. The viscosity of water decreases as temperature rises, as it is about 1.6 times at 10°C than at 30°C. We conduct the experiment from 9°C to 40°C, and observe how the temperature affects the results. Laser beam has a natural tendency to diffracts as it propagates. We change different beam waists and power to find the suitable conditions in which self-focusing balances diffraction, in which the beam diameter remains invariant during propagation, in other word, spatial solitons form. By these experiment results, we come up a hypothesis to explain the formation of the nanoparticle-concentration self-focusing mechanism.