Abstract

Optical coherent image amplification can be realized by means of two-beam coupling in photorefractive crystals. Image degradation due to the nonuniform pump beam depletion has been studied by Vachss and Yeh.¹ In this work, we present a theoretical analysis of the image degradation due to spatial gain variation at the Fourier transform domain. Since the photorefractive crystal is placed at the rear focal plane of the Fourier transform lens, different spatial components of the input image correspond to different coupling coefficients in the amplification process. This leads to a degradation of the output image. The degradation increases with D/f, where D is the aperture of the input image and f is the focal length of the Fourier transform lens. Strong degradation exists in the plane formed by the pump beam and the axis of the image-bearing beam. Experimental results with a 45° cut, 1.2 mm thick barium titanate crystal will be presented.

© 1992 Optical Society of America