Development of damage-resistant sputtered-oxide optical coatings for use at 248 NM

This report summarizes the results of a six-month effort to develop damage-resistant Kr*F laser mirrors by using and refining reactive sputter deposition techniques for the fabricaton of multilayer oxide optical coatings. Mirror performance goals included a reflectivity of 99% at 248 nm and a laser damage threshold of 5 J/cm2 for 20 ns pulses. Oxide multilayer coating combinations selected for development were SiO2/Al2O3, SiO2/HfO2 and SiO2/Y2O3. Selection was based on review and compilation of the optical properties of oxide materials reported in the recent literature. Twenty-eight coatings of selected designs were fabricated on LLNL substrates for laser damage testing by LLNL. Forty other coatings were fabricated on PNL substrates for optical, microstructural and topographical characterization by PNL aimed at optimization of their performance. Specimens for damage testing consisted of single layers of Al2O3, HfO2 and Y2O3 in thicknesses of lambda/2, 3lambda/2 and 2lambda at 248 nm plus high reflectors of the design LL (HL)/sup m/ HLL