Real-time holographic interferometry with double two-wave mixing in photorefractive crystals

We present a real-time holographic interferometer for which two reference w aves of different phases are created by two-wave mixing with a stationary s ignal wave in a photorefractive crystal. These waves are reconstructions of the stationary signal wave and interfere with the momentary (changing) sig nal wave in the manner of a holographic real-time interferometer. A fast ch ange (phase or intensity) of the signal wave leads to different intensity c hanges in both interferograms that are jointly used for evaluation. With an electric de field applied to the crystal, a high sensitivity for measuring phase changes (down to lambda/50, lambda = 633 nm) is found, and the sign of the phase change can be determined. (C) 2000 Optical Society of America.