Limited efficiency of a silver selenogallate optical parametric oscillator caused by two-photon absorption

The nonresonant two-photon absorption (TPA) coefficient in silver selenogallate (AgGaSe2) crystals was measured for both ordinary and extraordinary polarizations in the 1300-1600-nm wavelength range. We found a cutoff wavelength for the TPA at between 1400 and 1500 nn, which corresponds to half of the bandgap energy of the AgGaSe2 crystal. Below the cutoff wavelength we measured the TPA coefficient to be approximately 0.035 cm/MW for the extraordinary polarization and two to three times lower for the ordinary polarization. We compared the AgGaSe2 samples from two manufacturers and observed a factor of 2 difference in the TPA coefficients. Because of the high TPA, the 1.32-mum pumped AgGaSe2 optical parametric oscillator conversion efficiency was clipped at a low level. (C) 2001 Optical Society of America.