Abstract

Image amplification using photorefractive two-wave mixing is attractive since high gain and high signal-to-noise ratios are achievable using relatively low-power lasers. Huignard et. al. have achieved high gains in Bi₁₂SiO₂₀ (BSO) using the DC field and moving grating technique¹. The disadvantages of this technique are the uniform illumination and external frequency shift requirements. Another option is the use of alternating electric fields as suggested by Stepanov and Petrov². This technique has been demonstrated in BTO² and GaAs³. It maintains the 90^o phase shift between the incident fringe pattern and holographic grating required for image amplification, while allowing enhancement of the refractive index change via the external field. Other advantages include increased stability, no requirement for uniform illumination, and the avoidance of the electrode "shadowing" problem. In addition, the trap saturation regime (i. e. the maximum possible grating amplitude for a given material) can be reached at very high fields. The application of this technique to BSO has been suggested previously^2,3,4, and preliminary results are presented here.

© 1988 Optical Society of America