Pump beam depletion by inverse-ratio two-wave mixing in a BSO crystal

Abstract

Processing techniques such as image subtraction and logic operations using optical elements require the manipulation of light intensities. Usually, amplification of a signal is the required result but, as in the case of optical computing with gray-scale images, the depletion of light energy also becomes necessary. In a photorefractive crystal (PRC), energy transfer between two coherent beams of light may be achieved via two-wave mixing (2WM). The photorefractive effect is a bulk phenomenon in which a medium's index of refraction is modulated by incident light of spatially-varying intensity. Interference within the PRC between a strong pump beam and a weak signal beam leads to amplification of the signal. The gain is a function of the ratio between the beams.
Pump beam depletion of up to 67% via 2WM in an inverse-ratio configuration was successfully achieved. The depleted pump intensity and gain coefficient exhibit logarithmic behavior. The pump depletion approaches 0.39 for m > 0.01. For the specific crystal used, the gain coefficient Γ is approximately 0.95 cm⁻¹ for m > 0.01.