Fast near-infrared self-pumped phase conjugation with photorefractive Sn2P2S6

A significant improvement of the ring-cavity self-pumped phase conjugation response time in the near-infrared cw regime with a photorefractive brown Sn2P2S6 crystal is reported. Brown Sn2P2S6 is grown by the vapor-transport technique with SnI2 as the transport agent. With our Sn2P2S6 samples response times below 50 ms and phase-conjugate reflectivities of 25% can be achieved at a wavelength of 780 nm with a moderate light intensity of 1 W/cm2. We show that the measured reflectivity represents the limit given by the transmission of the ring-cavity arrangement. Reaching this limit is possible because of the large two-wave mixing gain of 18 cm-1 measured in this crystal.