Novel theoretical aspects on photorefractive ultrasonic detection and implementation of a sensor with an optimum sensitivity

We here expose theoretical and experimental results on homodyne detection using near-infrared laser sources, at 1.06, 1.32, and 1.55 mm wavelengths. The used photorefractive crystals are two large size CdZnTe:V samples. With speckled beams such as the ones scattered by diffusive objects, we reach a detection limit which, at 1.55 mm, is only 1.6 times above the one obtained with plane waves in a classical interferometer and only 2 and 2.2 times above at 1.32 and 1.06 mm, respectively. It is then demonstrated that the electron-hole competition, which varies enormously between these three wavelengths and gives a nearly zero two-wave-mixing gain at 1.32 mm, does not influence the sensitivity of the system. Moreover, we show that the frequency cutoff of the system is four times higher in the attenuation regime than in the amplification one