Large beam coupling gain in lnP:Fe using Franz–Keldysh electrorefractive photorefraction

Abstract

A beam-coupling gain of 19.1 cm−1 in InP:Fe has been achieved using near band edge photorefractive techniques. The conventional electro-optic photorefractive (EOPR) effect in semiconductors may be combined with the Franz–Keldysh electrorefractive photorefractive (ERPR) effect to produce large beam coupling gain coefficients. We have examined the effects using a tuneable Ti:sapphire laser in a pump/probe configuration and an applied electric field. Conventional EOPR creates a sinusoidal space-charge field (Esc) through carrier drift and diffusion, and the applied field (Edc) increases the magnitude of the applied space charge (Etot = Esc + Edc), as well as affecting the phase shift of Δn with respect to the intensity pattern. With appropriate temperature stabilization and ERPR, this phase shift can be maintained near ±90°, depending on the sign of Edc, determining the direction of energy transfer. We have characterized beam coupling gain, Γ, as a function of wavelength, intensity, temperature, grating spacing, and applied electric field and achieved a maximum Γ = 19.1 cm−1 at λ = 970 nm, T = 17 °C, Λ (grating wavelength) = 8.5 μm, IPump = 141 mW/cm2, and β (pump/probe ratio) ≈ 1000. Still higher gains have been seen using a moving grating technique, and the results will be presented at the conference.