Thermal enhancement of optical harmonic generation in a fiber-coupled nematic liquid crystal

Harmonic generation in a nematic liquid crystal

“…In the most of works [1,[3][4][5]14] on the GH, it is mainly either about LC with broken central symmetry (smectics, external fields), or about surface effects where inversion centers may initially be present. In all these works, it is assumed that the optical axis of the LC is rigidly fixed, which is fundamentally different from our research [7][8][9].…”

“…In previous papers [8,9], an NLC droplet sample was located directly at the end of the fiber optics (the diameter of core is 8.9 µm). This made it possible to obtain higher power densities of the pump radiation to achieve high (∼several percent) conversion factors to harmonics.…”

“…These factors also include influences that can be combined with one term-selfaction, which was first demonstrated in [2]. In laser irradiation, self-actions [2,[6][7][8][9], which deform the NLC and change the symmetry in the bulk, may include the light-induced Fredericks transition [10,11], thermo-mechanical [12], and thermo-orientation phenomena [13]. As a result, the generation of even harmonics seems to be divided into two consecutive stages: first, bulk deformation occurs, as a rule, leading to changes in the uniform direction of the optical axis (director) of the NLC in space and removing central symmetry, then nonlinear generation, as in solid crystals, occurs even harmonics.…”

“…Nonlinear optical phenomena in liquid crystals which are associated with the bulk conversion of the radiance frequency (harmonic generation, sum-frequency and differencefrequency generation) are phenomena that may eventually be of great applied value [6,7,14]. The features of the frequency conversion in LC mostly include the high efficiency of the process, which can reach several percent [7][8][9] at thicknesses of 10-100 microns. Such efficiencies, combined with small sizes, allow to create fairly simple and small-sized converters or optical parametric generators [9] to expand the frequency range of laser systems with relatively small (∼100 mW) average power.…”

“…Such efficiencies, combined with small sizes, allow to create fairly simple and small-sized converters or optical parametric generators [9] to expand the frequency range of laser systems with relatively small (∼100 mW) average power. In the previous works [8,9], a drop sample of a nematic LC (NLC) has been examined. It was applied directly to the end face of an fiber optic, so that it became possible to obtain the maximum power density of the pumped radiance for the laser systems.…”