Nanosecond optical parametric oscillators generating eye-safe radiation
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In this thesis, construction and characterization of nanosecond optical parametric oscillators (OPO’s) generating eye-safe radiation are presented. These OPO’s convert the output of an Nd:YAG laser at 1.06 μ,\ι\ wavelength to 1.57 μη\ wavelength which is in the eye-safe band of the spectrum. A potassium titanyl phosphate (KTP) crystal is employed in these OPO’s. In the experiments, output signal energies, pulse durations, spectral characteristics, and divergence angles of the OPO outputs have been measured. We have obtained 35% conversion efficiency by using pump pulses having 15 rnJ energy and 7 ns pulse duration. These low energy OPO’s can be used in range finders. We have also constructed OPO’s that are pumped by 100 mJ pulses of 15 ns pulse duration, and 38% conversion efficiency was achieved. These high energy OPO’s can be used in target designators. The divergence angles of the low energy and the high energy OPO’s hav(' been measured as 4 rnrad and 3 mrad, respectively. A numerical model which takes into account the temporal and spatial beam profiles, diffraction, and absorptions in the crystal has been constructed. The model is in qualitative agreement with the experimental results.