Laser damage threshold of single crystal ZnGeP<sub>2</sub> at 2.05 &#956;m

Kevin T. Zawilski; Scott D. Setzler; Peter G. Schunemann; Thomas M. Pollak

doi:10.1117/12.638607

7 February 2006 Laser damage threshold of single crystal ZnGeP₂ at 2.05 μm

Kevin T. Zawilski, Scott D. Setzler, Peter G. Schunemann, Thomas M. Pollak

Author Affiliations +

Proceedings Volume 5991, Laser-Induced Damage in Optical Materials: 2005; 599104 (2006) https://doi.org/10.1117/12.638607
Event: Boulder Damage Symposium XXXVII: Annual Symposium on Optical Materials for High Power Lasers, 2005, Boulder, CO, United States

Abstract

The laser damage threshold (LDT) of single crystal zinc germanium phosphide (ZGP), ZnGeP₂, was measured to be 2 J/cm² by the S-on-1 method. This LDT was double the previously measured value of 1 J/cm² and was achieved by improving the polishing technique for ZGP OPO crystals. ZGP is the nonlinear optical crystal of choice for laser frequency conversion in the 2-8 μm spectral range due to properties including its high non-linear coefficient (d₁₄=75 pm/V) and thermal conductivity (0.35 W/cm K). The surface preparation of ZGP parts was determined to be of great importance because laser-induced damage has been observed to always initiate at the surface rather than in the bulk of the material. In this study, the surfaces of ZGP parts fabricated in the same manner apart from the polishing stage were quantitatively examined. Two different polishing techniques were examined, and both uncoated and anti-reflection coated parts were examined for each polishing technique. Surfaces were characterized using scanning white light interferometry (SWLI) in order to determine RMS surface roughness and sample flatness. The photon backscatter technique (PBS) was used to determine the degree of surface and subsurface damage in the sample induced through the fabrication process. Statistical LDT was measured using a high-average-power, repetitively Q-switched Tm,Ho:YLF 2.05-μm pump laser. Laser induced damage was observed after each exposure by examining the site where the laser beam entered the ZGP sample using optical microscopy. On average, lower surface roughness and photon backscatter measurements were a good indicator of ZGP parts exhibiting higher LDT.

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Kevin T. Zawilski, Scott D. Setzler, Peter G. Schunemann, and Thomas M. Pollak "Laser damage threshold of single crystal ZnGeP₂ at 2.05 μm", Proc. SPIE 5991, Laser-Induced Damage in Optical Materials: 2005, 599104 (7 February 2006); https://doi.org/10.1117/12.638607

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