Abstract

Powerful IR radiation tunable in the wavelength range of 1.44-4.05 μm can be generated by an OPO of potassium niobate (KNbO₃) pumped by the fundamental of a pulsed Nd:YAG laser ¹. The OPO consists of a 10-mm-long AR- coated crystal (critical type-l phase-matching, θ=41°, ϕ=0°) placed in a 12-mm-long flat-flat mirror cavity resonant for the signal wave The energy density at threshold increases from 0.485 J/cm² at 1.9 μm to more than 0.7 J/cm below 1 48 μm. To avoid damage of the coating of the KNbO₃ crystal the pump energy densities should be less than 1 J/cm². Due to the rather large walk-off of 3.5° the threshold decreases with increasing pump beam diameter (from 0.6 J/cm³ at 2.35 mm to 0.485 J/cm² at 4,85 mm). Hence, enlarging the pump beam diameter front 3.05 mm to 4.85 mm. the OPO energy and efficiency increases at constant pump energy density (0.975 J/cm²) from 6.4 mJ to 30 mJ and from 9 % to 16.7 %, respectively.

© 1996 IEEE