Surface damage of extreme-ultraviolet gratings exposed to high-energy 20-fs laser pulses

The damage fluences of gratings for diffraction of ultraviolet radiation, w hich are used in high-order harmonic generation experiments, have been meas ured with respect to the fundamental laser beam radiation. We have tested g old and platinum coatings of 40- and 50-nm thickness, respectively, deposit ed onto fused-silica substrates, after irradiation of high-energy, spatiall y filtered, 20-fs laser pulses at 780 nm. The damage appears at a fluence o f similar to 0.3 J cm(-2) for gold and at a fluence of similar to 0.4 J cm( -2) for platinum. Scanning electron microscopy of the irradiated regions re vealed different damaging mechanisms for the two coatings. (C) 1999 Optical Society of America.