Mid-infrared (2.75-6.0-mu m) second-harmonic generation in LiInS2

Phase-matched second-harmonic generation is obtained in various LiInS2 crys tals by use of the tunable picosecond output of the free-electron laser for infrared experiments (FELIX) as the pump source in the mid-IR range from 2 .75 to 6.0 mum. Deviations from the phase-matching curve calculated from Bo yd's refractive-index data are observed. Furthermore, the optical damage th reshold of the crystals has been measured to be 1.1. J/cm(2) (>6 GW/cm(2)) at the 5-mum wavelength. LiInS2 holds great promise for parametric interact ion in the 1-13-mum range. (C) 2001 Optical Society of America.