The local structure of KH 2 PO 4 crystals (so-called KDP) at laser-induced damage sites created by irradiation with ∼ 3-ns, 355-nm laser pulses is studied by a combination of Raman scattering and photoluminescence spectroscopies. We compare spectra from pristine material, surface and bulk laser-induced damage sites, as well as from KPO 3 references. Results show that irradiation with fluences above the laser-induced breakdown threshold leads to stoichiometric changes at surface damage sites but

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... not at bulk damage sites. New spectroscopic features are attributed to dehydration products. For the laser irradiation conditions used in this study, the decomposed near-surface layer absorbs photons at ∼ 3.4 eV (364 nm). These results may help explain the recently reported observation that surface laser damage sites in KDP crystals tend to grow with subsequent exposure to high-power laser pulses, while bulk damage sites do not.