Impurities detection by optical techniques in KH2PO4 crystals

In this paper we examine how optical techniques can be used for impurities and defects detection in KH2PO4 (KDP) components. This is important in so far as some of these defects are responsible for a weaker than expected laser-induced threshold in these materials. Photothermal deflection, polariscopy, fluorescence and photoexcitation are investigated with the aim of localizing and identifying the laser-induced damage precursors. Impurities concentration is measured directly by ICP-AES and Fe is accordingly checked to be at the origin of a higher absorption in the prismatic sectors of rapidly grown KDP crystals. We also exhibit a fluorescence signal in the near-ultraviolet range by pumping at 248 nm; in rapidly grown crystals, in the same way as iron, the incorporation rate of the fluorescent centers is shown to depend on the growth sector.

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