Induced Molecular Reorientations in the Isotropic Phase

Laser-induced molecular reorientation is a common cause of optical nonlinearity in a fluid medium. In this respect, liquid crystals are often strongly nonlinear because of their large molecular anisotropy and strong correlation between molecules. The nonlinear optical properties of liquid crystals in the isotropic phase have already been studied quite extensively by a number of researchers in the past decade, This is, however, not true for liquid crystals in the mesophases. [Pg.107]

Quasielectric Light Scattering and Order Fluctuations in the Isotropic Phase 174 Nuclear Magnetic Resonance and Order Fluctuations in the Isotropic Phase. 175 Quasielastic Light Scattering and Orientational Fluctuations below Tc. . . 177 Nuclear Magnetic Resonance and Orientational Fluctuations below Tc.. .. 177 Optical Kerr Effect and Transient Laser-Induced Molecular Reorientation.. 181... [Pg.963]

Anisotropic molecules show optically isotropic behavior in the bulk when they are disordered and randomly oriented, for instance in solutions or liquid crystal above the transition temperature. Under the influence of a strong beam, the induced dipole moment of the molecules feels a torque that tends to orient the molecule. The reorientation of the molecular dipoles induces a change in the refractive index. The typical values for molecular susceptibilities and the time-responses vary depending on the type of systems. For small anisotropic molecular systems, x 10 esu, with a time response 10 s. However, in the nematic phase, liquid crystal molecules are strongly correlated, resulting in much higher values, x 10 esu,... [Pg.443]

Linear and nonlinear optical properties of liquid crystals in their mesophases have been studied in several contexts, in both fundamental and application-oriented pursuits. In the context of nonlinear optical processes, they have recently received considerable renewed interests as a result of the newly discovered extraordinarily large optical nonlinearity due to the laser-induced molecular reorientation, and a renewed effort explicitly at the large thermal index effect in liquid crystals. In the last few years, several groups [2]-[10] have looked at the optical nonlinearity in the mesophases of liquid crystals and the associated nonlinear processes. A brief review of some of these nonlinear optical processes and the fundamental mechanisms in both the liquid crystal and the isotropic phases has recently appeared [1]. In this paper, therefore, we will concentrate only on optical wave mixing processes that are relevant to this Special Issue. [Pg.214]