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In this article, we review the concepts of holographic and nonholographic organic-inorganic hybrids, both comprising a liquid crystal layer adjacent to inorganic crystalline windows. Photo-generated fields from photorefractive (holographic) or photovoltaic (nonholographic) crystalline windows govern the orientation of the liquid crystal molecules in the hybrid cells. Holographic hybrids have been used to demonstrate a high gain Bragg-matched beam coupling, whereas nonholographic hybrids have been used to demonstrate a lensing effect.

We show that photovoltaic fields generated internally in LiNbO3:Fe substrates are capable of efficiently reorienting liquid crystal molecules leading to new concepts of optically addressable light modulators. Using an arrangement consisting of a liquid crystal layer in contact with one or more LiNbO3:Fe photovoltaic substrates, we observe spatial filtering due to self-phase modulation in a planar oriented cell. The LiNbO3:Fe substrates are arranged such that light propagates along the +c axis, allowing a secondary process of power transfer to occur through photorefractive contra-directional two-beam coupling.

We report on the photorefractive properties of nematic liquid crystals sandwiched between windows of cerium doped strontium barium niobate (Ce:SBN). Unlike simple glass substrates, the Ce:SBN induces molecular pre-tilts that generate electric dipole moments in the liquid crystal through the flexoelectric effect. This enables the liquid crystal to become sensitive to the sign of the space-charge field and leads to an increase in the optical amplification when the cell thickness is decreased.

A nonlinear extinction of transmitted light is observed in liquid crystal cells with large concentrations of anthraquinone dye. Two distinct mechanisms are responsible for this effect when exposed to low and high intensity light, respectively. At low intensities, critical opalescence, micro-scatter, and an increase in linear absorption occur; whereas high intensities result in scattering from photo-induced micro-bubbles.

Optical and electrical measurements have been made on a new codoped potassium niobate crystal that yields a significant increase in linear absorption, photocurrent, and photorefractive beam coupling efficiency. The Ag impurity enters the K site, changing the local field in the lattice. The Fe in the Nb site, perturbed by the replacement of the next near-neighbor K with Ag, is responsible for the enhanced linear and nonlinear properties. The modified material parameters result in an increase of the photorefractive counter-propagating two-beam coupling efficiency.

In contra-directional two-beam coupling using photorefractive reflection gratings in LiNbO 3 :Fe, noise is observed in the form of quasi-periodic temporal instabilities. These instabilities result from different mechanisms that affect the magnitude of the space-charge field, and are attributed to the strong photovoltaic field generated in LiNbO 3 :Fe. A method of coating the z -surfaces of the crystal with a semi-transparent conductive coating eliminates these instabilities.

We investigate the use of a semiconductor optical amplifier operated in the saturation regime as a phase modulator for long range laser radar applications. The nature of the phase and amplitude modulation resulting from a high peak power Gaussian pulse, and the impact this has on the ideal pulse response of a laser radar system, is explored. We also present results of a proof-of-concept laboratory demonstration using phase-modulated pulses to interrogate a stationary target.

Oblique incidence of a weakly focused 532 nm laser beam on LiNbO3:Fe generates stimulated photorefractive backscatter (SPBS) from six-wave mixing in a reflection geometry. SPBS is analyzed through image restoration, interference experiments, and visibility measurements.

The dependence of self-pumped photorefractive two-beam coupling in Fe:KNbO3 with crystal angle has been measured at 532 nm for the a-c and b-c crystal planes using a combination of oil immersion and relay imaging. A significant deviation between existing theory and experiment is found for large crystal angles. We propose this is due to a highly anisotropic effective charge trap density in Fe:KNbO3 of almost two orders of magnitude variation with crystal angle in the a-c plane.

The spatial distribution of the power transfer achieved by contradirectional two-beam coupling using self-pumped photorefractive reflection gratings is investigated in two materials with different photorefractive gain coefficients, LiNbO3:Fe and KNbO3:Fe. Incremental portions of the volume grating are erased optically by inducing thin optical damage planes, reducing the overall two-beam coupling efficiency. By monitoring the effect of local grating disruption, the distribution of power transfer is spatially resolved throughout the crystal, and the results are found to be in agreement with our theoretical predictions.