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Proceedings Paper

Laser damage threshold of single crystal ZnGeP2 at 2.05 μm
Author(s): Kevin T. Zawilski; Scott D. Setzler; Peter G. Schunemann; Thomas M. Pollak
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Paper 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.

Paper Details

Date Published: 7 February 2006
PDF: 13 pages
Proc. SPIE 5991, Laser-Induced Damage in Optical Materials: 2005, 599104 (7 February 2006); doi: 10.1117/12.638607
Show Author Affiliations
Kevin T. Zawilski, BAE Systems (United States)
Scott D. Setzler, BAE Systems (United States)
Peter G. Schunemann, BAE Systems (United States)
Thomas M. Pollak, BAE Systems (United States)

Published in SPIE Proceedings Vol. 5991:
Laser-Induced Damage in Optical Materials: 2005
Gregory J. Exarhos; Arthur H. Guenther; Keith L. Lewis; Detlev Ristau; M.J. Soileau; Christopher J. Stolz, Editor(s)

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