Development of a nanosecond high energy KTA OPO operating at 2.9um

Summary form only given. We present the development of a KTA singly resonant optical parametric oscillator (OPO) with an unstable resonator. The OPO was pumped by a standard lamp-pumped, Q-switched, Nd:YAG laser (Continuum Surelight I) with 450 mJ output pulse energy in 5 ns pulses and 10 Hz repetition rate. The OPO was singly resonant for the idler wavelength, had an unstable resonator and was designed for optimal idler output energy of 30 mJ at 2.9 μm while minimising the linewidth of the free running OPO. The main reasons for choosing KTA were: low crystal loss in the wavelength range 2.6-3.2 μm; high non-linear coefficient; high optical damage threshold; low temperature sensitivity. KTA is also non-hygroscopic, and offers the possibility of critical phase matching with a high value of dλ/dθ which results in a narrow free running linewidth. The OPO system had a flexible design geometry incorporating the potential for both single- and double-pass of the pump beam through the 15 mm KTA crystal.