PROPAGATION OF A GAUSSIAN-PROFILE LASER-BEAM IN NEMATIC LIQUID-CRYSTALS AND THE STRUCTURE OF ITS NONLINEAR DIFFRACTION RINGS

We present experimental results on and a theoretical explanation of the laser- and electric-field-induced diffraction effect in both homeotropic and homogeneous nematic liquid-crystal (NLC) films. The diffraction effect is due to the Gaussian profile of a laser beam propagating in the liquid crystal. Many diffraction ring patterns under different electric and optical fields are compared and are analyzed. Some novel phenomena have been discovered. We have found that the diffraction ring pattern at a high electric field is much different from that at a low electric field. Rings in a pattern should be asymmetrical to one axis, and the outer ring interval should be wider. For the homogeneous NLC film it is possible that a second set of diffraction rings may occur when the electric field or the maximum optical field is larger than the tricritical field. The numerical result for the deformed wave-front profile of a Gaussian-profile laser beam passing through the NLC film is calculated. The results can explain these novel phenomena of diffraction ring structures. © 1990 Optical Society of America.