Experimental investigation of a photorefractive ring phase modulation amplifier

Abstract : We present the experimental investigation of a photorefractive ring phase modulation amplifier, that is not resonant and that can work with distorted beams. We show that with this geometry an amplification by a factor 5 of a phase modulation signal is possible. We also show that this strong amplification is alleviated by the presence of losses in the ring. These losses lead to a real gain in signal to noise ratio of a factor 3, that nevertheless expresses that with such a system the photon noise limit of laser ultrasonics system can be overpassed. The losses are also responsible for the strong sensitivity of the system to the vibrations, which puts a strong limitation of the ring amplifier