Analysis of high-resolution scatter images from laser damage experiments performed on KDP

Michael J. Runkel; Bruce W. Woods; Ming Yan; James J. De Yoreo; Mark R. Kozlowski

doi:10.1117/12.240397

27 May 1996 Analysis of high-resolution scatter images from laser damage experiments performed on KDP

Michael J. Runkel, Bruce W. Woods, Ming Yan, James J. De Yoreo, Mark R. Kozlowski

Author Affiliations +

Proceedings Volume 2714, 27th Annual Boulder Damage Symposium: Laser-Induced Damage in Optical Materials: 1995; (1996) https://doi.org/10.1117/12.240397
Event: Laser-Induced Damage in Optical Materials: 1995, 1995, Boulder, CO, United States

Abstract

Interest in producing high damage threshold KH₂PO₄ (KDP) and (D_xH_1-x)₂PO₄ (KD^*P, DKDP) for optical switching and frequency conversion applications is being driven by the system requirements for the National Ignition Facility (NIF) at Lawrence Livermore National Lab (LLNL). Historically, the path to achieving higher damage thresholds has been to improve the purity of crystal growth solutions. Application of advanced filtration technology has increased the damage threshold, but gives little insight into the actual mechanisms of laser damage. We have developed a laser scatter diagnostic to better study bulk defects and laser damage mechanisms in KDP and KD^*P crystals. This diagnostic consists of a cavity doubled, kilohertz class, Nd:YLF laser (527 nm) and high dynamic range CCD camera which allows imaging of bulk scatter signals. With it, we have performed damage tests at 355 nm on four different `vintages' of KDP crystals, concentrating on crystals produced via fast growth methods. We compare the diagnostic's resolution to LLNL's standard damage detection method of 100X darkfield microscopy and discuss its impact on damage threshold determination. We have observed the disappearance of scatter sites upon exposure to subthreshold irradiation. In contrast, we have seen scatterers appear where none previously excited. This includes isolated, large (high signal) sites as well as multiple small scatter sites which appear at fluences above 7 J/cm² (fine tracking). However, we have not observed a strong correlation of preexisting scatter sites and laser damage sites. We speculate on the connection between the laser-induced disappearance of scatter sites and the observed increase in damage threshold with laser conditioning.

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Michael J. Runkel, Bruce W. Woods, Ming Yan, James J. De Yoreo, and Mark R. Kozlowski "Analysis of high-resolution scatter images from laser damage experiments performed on KDP", Proc. SPIE 2714, 27th Annual Boulder Damage Symposium: Laser-Induced Damage in Optical Materials: 1995, (27 May 1996); https://doi.org/10.1117/12.240397

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