Picosecond laser-induced reorientation, density, temperature, and flow effects in the mesophases of liquid crystals

Nonlinear light scatterings in the mesophases of liquid crystals with nanosecond laser pulses have demonstrated the possibility of inducing large refractive index changes associated wtih 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. The results of a study which used picosecond laser pulses to unambiguously create and measure these nonlinear effects associated with thermoelastic, electrostrictive, and dipolar interactions and their dynamics are reported. 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.