Ab initio theory of linear and nonlinear optics of liquid crystals.

A new theory of linear and nonlinear optics o crystals is presented. It is based on the ab initio microscopic Lagrangian theory of Lax and Nelson for anisotropic crystals and the dissipation function theory of Lam and Lax for liquid crystals. The theory is completely deductive and the effects of internal excitations can be included in principle. In this paper the formalism is presented with application to nematic liquid crystals. Dielectric constants with frequency dependence are given. Within the electric dipole approximation an effective equation of motion for the director is derived. It agrees with that of Zel'dovich, et al. This equation describes the optically induced reorientation of the molecules. Flexoelectric constants depending on the optical frequency are presented. The flexoelectric effect in our case arises from the induced dipoles due to director gradients and should exist even in molecules without permanent dipoles or quadrupole moments. The physical mechanism differs from that proposed by Meyer and by Prost and Marcerou. Dissipative effects are also discussed with the use of a dissipation function.