Cadmium silicon phosphide, CdSiP2 or CSP, exhibits the highest nonlinear Figure of Merit (d2/n3) among all bulk birefringent crystals that can be pumped at wavelengths ≤ 2 microns - and the highest among all nonlinear optical (NLO) crystals at any wavelength with practically low absorption losses. Although a 2-micron pumped optical parametric oscillator (OPO) and numerous 1-micron-pumped CSP OPOs have been demonstrated previously, here we report the first 1.5-micron-pumped CSP OPO.
The pump laser for this experiment was a non-critically phase-matched (NCPM) KTP singly-resonant OPO generating 6.3 ns, 10 mj pulses at 1.57 microns, which was in turn pumped by a 1.064-m 5-Hz, 7-ns, 20-mJ Nd:YAG laser. The 1.57-m signal from the KTP OPO pumped a 5x5 mm2 x 5.5-mm long CSP crystal cut for type I phase matching at 63°) inside a linear flat-flat cavity. The measured absorption coefficient at 1570 nm was approximately 0.015cm-1. The input mirror was highly transmitting (97%T) at 1.57 microns and highly reflective from 2.5 to 3.8 microns. The best results were achieved at signal and idler wavelengths of 2.67 microns (50%R output coupling) and 3.83 microns (30%R output coupling) respectively, yielding 2.24 mJ of combined signal and idler output energy for a total optical conversion efficiency of 32%. The slope efficiency was 42%. At 66 MW/cm2 pump peak intensity the OPO was running nearly 4 times over threshold with no signs of roll-over. The CSP crystal was angle-tuned to produce output wavelengths ranging from 2.2 microns to 5.05 microns.
Leonard A. Pomeranz, John C. McCarthy, Randy C. Day, Kevin T. Zawilski, and Peter G. Schunemann, "First 1.57-Micron-Pumped CdSiP2 Optical Parametric Oscillator (Conference Presentation)," Proc. SPIE 10516, Nonlinear Frequency Generation and Conversion: Materials and Devices XVII, 105160Z (Presented at SPIE LASE: January 31, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2291350.5751428850001.
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