X-ray absorption analysis of KDP optics

Potassium dihydrogen phosphate (KDP) is a non-linear optical material used for laser frequency conversion and optical switches. Unfortunately, when KD P crystals are coated with a porous silica anti-reflection coating (Thomas, Appl. Opt. 1986;25(9):1481) and then exposed to ambient humidity, they dev elop dissolution pits (Wheeler et al., SPIE 1999;3902:451-459; Wheeler et a l., Mater. Res. Sec. Conf., San Francisco, 2000). Previous investigations ( Wheeler et al., SPIE 1999;3902:451-459) have shown that thermal annealing r enders KDP optics less susceptible to pitting, suggesting that a modificati on of surface chemistry has occurred. X-ray absorption was used to characte rize changes in the composition and structure of KDP optics as a function o f process parameters. KDP native crystals were also analyzed to provide a s tandard basis for interpretation. Surface sensitive total electron yield an d bulk sensitive fluorescence yield from the K2p, P2p (L-2,L-3-edge) and O1 s (K-edge) absorption edges were measured at each process step. Results ind icate that annealing at 160 degreesC dehydrates the surface of KDP resultin g in a metaphosphate surface composition with K:P:O=1:1:3. (C) 2001 Elsevie r Science BN. All rights reserved.