Abstract

Recent investigations have shown that photorefractive semiconductors have attractive features such as fast response times and operation at near-IR wavelengths for optical image processing applications. However, these advantages cannot be utilized fully unless efficient photorefractive effects in these can be demonstrated. Recently, by applying external electric fields to the crystals, the net photorefractive gain using compound semiconductors has been demonstrated for GaAs:Cr under a dc electric field with a moving grating and for lnP:Fe and undoped GaAs under a square-wave ac electric field. Here we report for the first time, we believe, the observation of net gain using undoped GaAs under a dc electric field only (i.e., without a moving grating) at 1.06 μm. In our experiments the pump and probe beam intensities were 8 and 0.13 mW/cm², respectively. The crystals used were grown by the medium pressure LEC technique with As injection. The sample size was 10 × 6 × 5.4 mm along the $\text{[110][}\overline{\text{1}}\text{10]}$, and [001] crystal orientations, respectively. The $\text{[}\overline{\text{1}}\text{10]}$ sample surfaces were optically polished and anti-reflection coated. The electrodes (Znln) were vacuum deposited on the [001] crystal surfaces. The largest gain coefficient measured was 2.6 cm⁻¹, while the absorption coefficient measured was 1.3 cm⁻¹, indicating a large net gain.

© 1988 Optical Society of America