Nonlinear-optical processes in nematic liquid crystals near Freedericks transitions

Weak-beam amplification and diffracted-beam production are predicted under a variety of conditions, in which thin nematic-liquid-crystal samples maintained in an external magnetic field near Freedericks transitions are simultaneously illuminated by strong and weak beams derived from the same light source. It is shown that for 4-methoxybenzylidene-4′-butylaniline, substantial weak-beam amplification should occur under continuous illumination for modest (∼ 0.1 W/${\mathrm{cm}}^2$) strong-beam intensities, for certain cell and beam geometries. If a small positive frequency difference between the strong and weak incident beams is maintained, weak-beam amplification is further enhanced, and the conditions on the angles of incidence for amplification are considerably relaxed.