Variations in refractive indices with temperature, the thermo-optic co
efficients and temperature-dependent absorption in AgGaSe2 crystal hav
e been measured. Good agreement between the theory and experiment has
been found for the temperature-dependence of phase-matching angles for
second-harmonic generation of CO2 laser radiation in this crystal. He
nce variations of the phase-matching angle with temperature in some im
portant nonlinear devices have also been estimated.