Simultaneous determination of the index and absorption gratings in multiple quantum well photorefractive devices designed for laser ultrasonic sensor

摘要

A method to determine complex amplitudes of index and absorption gratings in photorefractive multiple quantum wells is presented. Usually to evaluate these parameters, spectral measurement of absorption change due to the applied field over a wide wavelength range is required and the index change is calculated through the Kramers-Kronig's relationship. In our method, only a set of measured data for a photorefractive two-wave mixing set-up with small sinusoidal phase modulation for fixed wavelength is needed. This is thus well adapted to in situ characterization of systems that operate at a fixed wavelength. Real and imaginary part of the gains owing to the index and the absorption gratings are calculated from the output signals of the system. We apply this method to our photorefractive multiple quantum well devices operating at 1064 nm, and obtain consistent results.