CHARACTERIZATION OF PHOTOREFRACTIVE CDTE-V - HIGH 2-WAVE MIXING GAIN WITH AN OPTIMUM LOW-FREQUENCY PERIODIC EXTERNAL ELECTRIC-FIELD

We present two-wave mixing results obtained with CdTe:V photorefractiv e crystals under an external dc or low-frequency square-shaped periodi c electric field. The majority photorefractive carriers are holes at 1 .32 and 1.54 mum, whereas electrons dominate slightly at 1.048 mum. At this wavelength an intensity-dependent resonant gain enhancement is o bserved in the presence of a dc field. The effective trap densities ar e near 10(15) cm-3. The highest gains (to as high as 11 cm-1 for a fie ld amplitude of 15 kV/cm at 1.32 mum) are obtained with a square-shape d periodic field at an optimum frequency F0. The dependence of F0 on t he different experimental parameters is presented. A two-level model i n which the secondary level has a thermal emission rate much larger th an the principal one qualitatively describes this nonstandard frequenc y behavior.