Crucial influence of the twist deformation on degenerate four-wave mixing process in homeotropically aligned nematic liquid crystals

Abstract

The diffraction efficiency suppression and peak shifting from the Freedericksz threshold voltage are predicted for degenerate four-wave mixing process in a low-frequency ac voltage-biased homeotropically aligned nematic liquid crystal film. The crucial factor is the twist deformation in the induced phase grating. Significant amounts of diffraction efficiency suppression and peak shift are shown both in numerical and experimental results.

Nonlinear Birefringence in Electrically Biased Hybrid Aligned Nematics

“…However, as shown in Figure 5 , it is negative for 5CB with a positive dielectric anisotropy. The phase retardation difference is proportional to the biased voltage in agreement with the prediction of Equation (8). The slope of the Equation (8) The discrepancy of data for MBBA with 0.5 volts biased voltage in higher intensity regime on Figure 3 can be explained by thermal effect.13 In general,', the rate of change of index with respect to temperature An,/AT is negative while An,/ AT is positive.…”

“…The degenerate four wave mixing is crucially influenced by the biased electric field, too. 8 In this paper, the birefringence controlled byelectric and/or optical fields is studied for HAN cell for NLC of either positive or negative dielectric anisotropy. The continuum theory is used in the derivation for field-induced molecular reorientation angles and birefringence.…”

Double peaks of fundamental diffraction efficiency versus biasing of electric fields through the degenerate four-wave mixing process in nematic liquid-crystal films

“…(6). This can be explained by the twist-deformation effect discussed in our previous paper, 12 i.e., the term (K 2 / K 3 ) (2d/A) 2 in relation (2), since the smaller the grating period is, the less deep the grating modulates. According to the behavior of the phase-amplitude curve shown in Fig.…”

Optical phase conjugation in a nematic liquid-crystal film modulated by a quasi-static electric field

“…The first-order DFWM diffraction efficiency reaches its maximum at a biased ac voltage that depends on the elastic constant, the sample thickness, and the grating period. 3,4 In other words, the diffraction efficiency can be modulated by the biased voltage. This is important in applications utilizing DFWM, such as optical phase conjugation (OPC).…”