Orientational photorefractive effects in nematic liquid crystal films

We present a detailed theoretical discussion of the fundamental mechanisms for the recently observed nonlinear electro-optical effects in nematic liquid crystal films. Detailed expressions for the three principal mechanisms for space charge fields formation and various dielectric, conductivity and flow induced torques that are responsible for the liquid crystal director axis reorientation process are derived. We have observed strong optical wave mixing effects such as two-beam energy coupling and self-diffraction; the observed effects, their magnitude and dynamics, and dependencies on various physical parameters are found to be in good agreement with theories.