Picosecond Laser-induced Reorientation, Density, Temperature, And Flow Effects In The Mesophases Of Liquid Crystals

Previous studies of nonlinear light scatterings in the mesophases of liquid crystals with nanosecond laser pulses have demonstrated the possibility of inducing large refractive index changes associated with photo-induced fluctuations in density, temperature, and director-axis orientations. High frequency acoustic waves, with periods on the order of a few nanoseconds, have also been observed. In this paper, we report the results of a study where we employed picosecond laser pulses to unambiguously create and measure these nonlinear effects associated with thermoelastic, electrostrictive and dipolar interaction, and their dynamics. A quantitative theory based on solving the full hydrodynamically coupled equations for the density and temperature changes, an Erickson-Leslie type of equation for the laser-induced director-axis reorientation, and the hydrodynamic equation for the flow phenomenon, is also presented for the first time.