Reorientation In Nematic Liquid Crystals Research Articles

Nonlinear Diffraction of CW-Laserbeams by Spatial Selfphase-Modulation in Nematic Liquid Crystals

Abstract Optical nonlinearities in nematic liquid crystals lead to strong self-defocussing and nonlinear diffraction effects with low power laser intensities of some hundred Watts/cm2. We describe these diffraction effects by expanding the transversally modulated intensity behind the sample into gaussian beams. Using in addition a simple model of light-induced reorientation of nematic liquid crystals as nonlinear mechanism, we get good agreement between theory and self-diffraction experiments, which have been done in the liquid crystal 5CB.

Optically-induced molecular reorientation in nematic liquid crystals and nonlinear optical processes in the nanoseconds regime

We present a detailed theoretical analysis and experimental study of purely optically-induced nematic axis reorientation and the associated nonlinear optical processes such as self-phase modulations and optical switching. It is shown that under a sufficiently intense laser field (∼ 100 MW/cm2), nematic liquid crystals will respond in the nanosecond regime. Single nanosecond laser pulse self-phase modulation and intensity switching effects are observed. The magnitude and dynamics of the response are in agreement with theoretical expectations. Optical power limiting and switching effects associated with self-phase modulations are also demonstrated.

Dynamic hysteresis during the reorientation of nematic liquid crystals in pulsed fields

It is shown that use of the Lavrent'ev-Ishlinskii method in the study of real optical cells based on nematic liquid crystals, enables the experimentally observed deviations in the nature of light transmission by the optical cells at the leading and trailing front of a strong magnetic field acting on the liquid crystal to be explained. The field has the form of a square wave pulse of considerable duration.

Photonic logic based on molecular reorientation of nematic liquid crystals

A new type of photonic logic, based on the use of nematic liquid crystals is proposed. The system takes advantage of the refractive-index changes induced by laser beams. Examples of AND, OR and NOR functions are presented.

Laser Induced Reorientation of Nematic Liquid Crystals

Abstract A significant increase of the divergence and appearance of a fringe system has been observed by illuminating of MBBA (p-n-methoxybenzilidene-p-butylaniline) and OCB (octyl-cyano-biphenyl) nematic liquid crystalline samples with a collimated beam of an argon ion laser. The dependence of this effect on laser power, beam polarization, and angle of incidence has been studied in homeopolar and planar sandwich-like cells of 50-150 μm thickness, in the nematic phase. At a homeopolar cell of MBBA (150 μm thickness), at normal incidence a threshold laser power of 45 m W was found. The phenomena can be explained as deformation of the orientation by the Fredericks effect due to light fields. The observations are in good agreement with the theoretical predictions including an estimation of the laser power threshold.