THERMAL LENSING IN SILVER GALLIUM SELENIDE PARAMETRIC OSCILLATOR CRYSTALS

We performed an experimental investigation of thermal lensing in silve r gallium selenide (AgGaSe2) optical parametric oscillator crystals pu mped by a 2-mum laser at ambient temperature. We determined an empiric al expression for the effective thermal focusing power in terms of the pump power, beam diameter, crystal length, and absorption coefficient . This relation may be used to estimate average power limitations in d esigning AgGaSe2 optical parametric oscillators. We also demonstrated an 18% slope efficiency from a 2-mum pumped AgGaSe2 optical parametric oscillator operated at 77 K, at which temperature thermal lensing is substantially reduced because of an increase in the thermal conductivi ty and a decrease in the thermal index gradient dn/dT. Cryogenic cooli ng may provide an additional option for scaling up the average power c apability of a 2-mum pumped AgGaSe2 optical parametric oscillator.