Investigation of the electronic and physical properties of defect structures responsible for laser-induced damage in DKDP crystals.

Laser-induced damage at near operational laser excitation conditions can limit the performance of potassium dihydrogen phosphate (KH(2)PO(4), or KDP) and its deuterated analog (DKDP) which are currently the only nonlinear optical materials suitable for use in large-aperture laser systems. This process has been attributed to pre-existing damage precursors that were incorporated or formed during growth that have not yet been identified. In this work, we present a novel experimental approach to probe the electronic structure of the damage precursors. The results are modeled assuming a multi-level electronic structure that includes a bottleneck for 532 nm excitation. This model reproduces our experimental observations as well as other well-documented behaviors of laser damage in KDP crystals. Comparison of the electronic structure of known defects in KDP with this model allows for identification of a specific class that we postulate may be the constituent defects in the damage precursors. The experimental results also provide evidence regarding the physical parameters affecting the ability of individual damage precursors to initiate damage, such as their size and defect density; these parameters were found to vary significantly between KDP materials that exhibit different damage performance characteristics.