Exfoliation of optical thin films at high humidity in the air is serious problem. Deterioration of three kind of optical thin films deposited on three types of substrate with different water-resistance (phosphate glass LHG-8, BK-7, and fused silica glass) at high humidity condition was studied. Thin films deposited on fused silica glass with highest waterresistance showed a best result for the exfoliation problem. Silica film seemed to be best for the surface observation at high humidity, but the laser-induced damage threshold(LIDT) was considerably lowered.

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Laser-induced bulk damage of various types of silica glasses at 266 nm with pulse widths of 4 ns and 30 ps was measured. At a single pulse, the laser-induced damage thresholds (LIDTs) of fused quartz (FQ) produced by melting natural quartz powder were greater than those of synthetic fused silica (SFS), and a SFS containing 40 ppm of OH had the highest LIDT among the SFSs. The LDITs of SFSs containing no OH were less than those of the other samples. At 12000 pulses, the difference in LIDT among all samples became small.

Laser-induced bulk-damage threshold (LIDT) of various types of silica glasses at 532 and 355 nm caused by lasers with pulse widths of %5 ns (refered as nanosecond laser [NSL]) and 30 ps (refered as picosecond laser [PSL]) were observed. The LIDTs of fused quartzes (FQs) produced by melting natural quartz powder were less than those of synthetic fused silicas (SFSs) at both wavelengths. At 355 nm, the LIDT of SFS containing 1000 ppm of Cl was almost the same as that of FQ at 1 pulse, and that at 12000 pulses was between those of SFSs and FQs. The variation of LIDT among samples for PSL is less than that for NSL.

High-average-power, highly efficient solid-state lasers are desirable, especially for application to material processing, X-ray generation and pumping source of Ti: sapphire laser. In these applications, a large host material to irradiate high energy are required. A laser glass of a large size with an optical homogeneity of ± 1× 10-6 can be easily obtained, but high-frequency operation of glass laser is limited due to the low thermal conductivity of glass. Dane1 operated the Nd :glass flashlamp-pumped zig-zag amplifier at maximum repetition frequency of 3Hz. The array Nd:glass slab laser2 could be operated at higher repetition frequency. In this paper, the optical characteristics of the array Nd:glass slab laser operated at high repetition frequency are shown.