| Optical wave-mixing has a lot of applications such as optical amplification, adaptive optics, harmonic wave generation, and multi-photon microscopy. Photorefractivity has been utilized in many important applications including high density optical data storage, image processing, spatial light modulation, phase conjugation, and optical limiting. They have been investigated, theoretically and experimentally, in this thesis, in the contexts of stimulated orientational scattering and photorefractivity in liquid crystals.; Stimulated orientational scattering is a unique optical wave-mixing phenomenon that a scattered noise beam, generated by liquid crystal director oscillation, gets amplified through its interaction with the transmitted beam and director reorientation grating under an intense laser illumination. In this research work, I developed the first steady-state SOS theory without the compromise of non-pump-depletion approximation. I successfully implemented polarization conversion in the infrared wavelength regime and the experimental observations agree well with our developed theory. The control of an external AC field to the stimulated orientational scattering was also experimentally investigated.; Furthermore, I investigated the dynamics of this liquid crystal director reorientational process by analyzing the Fourier spectrum of the stimulated signal. The influence of a modulating AC field to the stimulated signal was also studied. The oscillating frequency of the liquid crystal director grating agreed with theoretically calculated characteristic frequency.; In addition, I have theoretically and experimentally studied the photorefractivity in liquid crystals. Based on the transport band model, the generated space charge field was developed. With the help of an externally applied DC field, the space charge field is able to induce liquid crystal director reorientation and analytical solutions have been derived for both the director reorientational angle and the resulting refractive index grating. Single-wall carbon nanotube doped liquid crystal films showed a big increase in the effective optical nonlinearity compared with previous reported results in dye doped photorefractive liquid crystals. The generation of the diffractive grating in the pure and Methyl-red doped liquid crystals has also been theoretically studied and the absence of the two-beam amplification has been explained as well.; In the last, this investigation in optical wave-mixing and photorefractivity in liquid crystal is concluded and the future works are proposed. |
