Gain exceeding absorptive losses in photorefractive GaAs

K Walsh, TJ Hall - Applied optics, 1989 - opg.optica.org
Applied optics, 1989opg.optica.org
The photorefractive effect is of considerable interest for parallel optical processing
operations. Semiconductor materials have received attention because of their potentially fast
effect,[1] the lack of optical activity,[2] and their sensitivity at wavelengths compatible with
diode lasers and diode-pumped solid-state lasers.[3],[4] To implement practical systems,
however, enhancement techniques are required to overcome the disadvantage of the
relatively low electrooptic coefficients of the semiconductor materials. Two proposed …
Abstract
The photorefractive effect is of considerable interest for parallel optical processing operations. Semiconductor materials have received attention because of their potentially fast effect,[1] the lack of optical activity,[2] and their sensitivity at wavelengths compatible with diode lasers and diode-pumped solid-state lasers.[3],[4] To implement practical systems, however, enhancement techniques are required to overcome the disadvantage of the relatively low electrooptic coefficients of the semiconductor materials. Two proposed enhancement techniques involving applied electric fields are first, a dc field with an intensity interference pattern moving through the crystal [5] or second, a stationary interference pattern with an applied ac electric field.[6] This second technique has many advantages over the first, particularly its nonresonant nature with the lack of dependence on intensity that this implies, allowing enhancement over an arbitrarily long interaction length. This second technique has been applied to GaAs.[7] Although results are described in terms of two-wave mixing gain, no real amplification is achieved because the absorption coefficient must always be subtracted, leaving a net loss. In this Letter we describe our measurement of two-wave mixing gain exceeding absorption in Cr-doped GaAs at 1.09 μm.
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