Enhanced responsivity of non-steady-state photoinduced electromotive force sensors using asymmetric interdigitated contacts.

The responsivity at a constant detection area of non-steady-state photoinduced electromotive force (photo-emf) detectors is improved by a factor equal to the number of contact pairs contained in asymmetric interdigitated surface contacts. The polar nature of photo-emf current generation requires contact asymmetry in which one increases the total signal by blocking the illumination between alternate contact pairs, in distinct contrast to the behavior of conventional interdigitated contacts fabricated upon isotropic photoconductors.

Powerful, diffraction-limited semiconductor laser using photorefractive beam coupling.

We use semiconductor laser amplifiers and a photorefractive crystal to generate a high-power, diffraction-limited laser beam at 860 nm. Using a single flared amplifier, we obtain 1.09 W in a diffraction-limited beam from 2.2 W of pump power. Using an array of flared amplifiers, we also demonstrate efficient beam coupling, showing that this technique is easily extended to semiconductor amplifier arrays.

Ultralong dark decay measurements in BaTiO(3).

We have observed dark decay rates in BaTiO(3) crystals at elevated temperatures that correspond to dark decay times as long as 2200 years at room temperature. Our investigations have shown that cerium is a desirable dopant in BaTiO(3) for enhancing the dark storage time.

Measurement of the photorefractive phase shift.

We present a method to separate the effects of trap gratings and electro-optic gratings in BaTiO(3) crystals, and we determine the true spatial shift between the electro-optic grating and the optical intensity pattern. At small beam-crossing angles this spatial shift is strongly affected by a photogalvanic current in the crystal.

Measuring photorefractive trap density without the electro-optic effect.

Two optical beams can couple in a photorefractive crystal without using the electro-optic effect. Beam coupling is due to a spatially modulated absorption caused by the rearrangement of trapped charges. We use these gratings to determine the effective photorefractive trap density for several barium titanate crystals.

Self-scanning of a continuous-wave dye laser having a phase-conjugating resonator cavity.

A continuous-wave dye laser having a self-pumped phase conjugator in place of its usual output mirror will slowly change its own output wavelength with time. The laser has a bandwidth of 1.5 GHz and can self-scan to either longer or shorter wavelengths over a 37-nm range. The phase conjugator uses self-pumped four-wave mixing in a BaTiO(3) crystal. A ring laser that uses two-wave mixing in the same crystal is also observed to have a frequency offset of a few hertz compared with the frequency of the pumping beam. These two effects are related; both are caused by a spontaneously moving photorefractive-index grating in the BaTiO(3) crystal.