Abstract

The laser-induced damage threshold (LIDT) of single-crystal zinc germanium phosphide (ZGP), ${\mathrm{ZnGeP}}_2$, was increased to $2\mathrm{J}∕{\mathrm{cm}}^2$ at $2.05\mathrm{\mu }\mathrm{m}$ and a $10\mathrm{kHz}$ pulse rate frequency (double the previously measured value of $1\mathrm{J}∕{\mathrm{cm}}^2$). This increased LIDT was achieved by improving the polishing of ZGP optical parametric oscillator crystals. Two different polishing techniques were evaluated. Surfaces were characterized using scanning white-light interferometry to determine rms surface roughness and sample flatness. The photon backscatter technique was used to determine the degree of surface and subsurface damage in the sample induced through the fabrication process. The effect of subsurface damage in the samples was studied by removing different amounts of material during polishing for otherwise identical samples. Statistical LIDT was measured using a high-average-power, repetitively Q-switched Tm,Ho:YLF $2.05\mathrm{\mu }\mathrm{m}$ pump laser. On average, lower surface roughness and photon backscatter measurements were a good indicator of ZGP samples exhibiting higher LIDT. The removal of more material during polishing significantly improved the LIDT of otherwise identical samples, indicating the importance of subsurface damage defects in the LIDT of ZGP.

© 2006 Optical Society of America

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