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Single-mode optical parametric oscillator

A tunable KTP optical parametric oscillator (OPO) operating on a single longitudinal mode of its resonator is described. Single mode operation has been achieved by using an intracavity Fabry-Perot etalon in a short-length OPO resonator. The crystal is pumped by the second harmonic of a 10 Hz, Q-switched, injection-seeded Nd:YAG laser. the tuning range observed with a crystal cut at 60 degrees is 0.75 - 0.87 micrometer for the signal beam and 1.83 - 1.37 micrometer for the idler beam. The linewidth of the OPO is 200 MHz (0.0066 cm-1), which is very close to the Fourier limit. The total output energy (signal plus idler) was measured to be up to 0.6 mJ per pulse at a pump energy of 10 mJ.