Jennifer L. Carns

Substrate Induced Pre-tilt in Hybrid Liquid Crystal/Inorganic Photorefractives

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.

Photovoltaic Field-Induced Self-Phase Modulation of Light in Liquid Crystal Cells

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.

Spatial distribution of power coupling in self-pumped photorefractive reflection gratings

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.

Saturated Semiconductor Optical Amplifier Phase Modulation for Long Range Laser Radar Applications

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.

Analysis of Stimulated Photorefractive Backscatter during Six-Wave Mixing in Lithium Niobate

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.

New Phenomena in Dye-Doped Liquid Crystals: Black Hole Effect and Switchable Reversed Diffraction (Postprint)

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.