A CrTmHo:YAG laser pumped ZnGeP2 optical parametric oscillator for mid-infrared spectroscopy

We report a singly resonant optical parametric oscillator (SRO) based on a ZnGeP2 crystal directly-pumped by a lamp-pumped Q-switched CrTmHo:YAG laser. The IR wavelength was tuneable from 4.7 μm to 7.8 μm via crystal angle tuning. A maximum optical to optical efficiency of 56% was obtained from pump (2.09 μm) to total IR at a pump energy of 6.5 mJ. The corresponding idler energy was 1.45 mJ. The SRO was measured to have a slope efficiency of 64% and a threshold of 1 mJ. The spatial beam quality of the idler, characterized by the M2 parameter, was 1.38 when the SRO was pumped at 2.5 times threshold. These results show that ZnGeP2 OPOs directly pumped by a CrTmHo:YAG laser can be operated efficiently, while maintaining good IR beam quality. The wide tuning range and a high pulse energy makes this SRO particularly suitable for spectroscopic applications, and, tests in the field medical application, e.g., for cutting of soft tissue during surgery or corneal corrections.

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