Mechanically polished fused silica surfaces were heated with continuous-wave CO(2) laser radiation. Laser-damage thresholds of the surfaces were measured with 1064-nm 9-nsec pulses focused to small spots and with large-spot, 1064-nm, 1-nsec irradiation. A sharp transition from laser-damage-prone to highly laser-damage-resistant took place over a small range in CO(2) laser power. The transition to high damage resistance occurred at a silica surface temperature where material softening began to take place as evidenced by the onset of residual strain in the CO(2) laser-processed part. The small-spot damage measurements show that some CO(2) laser-treated surfaces have a local damage threshold as high as the bulk damage threshold of SiO(2). On some CO(2) laser-treated surfaces, large-spot damage thresholds were increased by a factor of 3-4 over thresholds of the original mechanically polished surface. These treated parts show no obvious change in surface appearance as seen in bright-field, Nomarski, or total internal reflection microscopy. They also show little change in transmissive figure. Further, antireflection films deposited on CO(2) laser-treated surfaces have thresholds greater than the thresholds of antireflection films on mechanically polished surfaces.
Theoretical and numerical analysis of the multipass amplifier illustrates its flexibility in applications ranging from efficient high-power pulse amplification to short-pulse generation with great amplitude and pulse-width stability.
Scandium oxide has proved to be a damage-resistant high-index material in laser coatings for use at 248 nm. The results of damage threshold measurements on laser reflectors and antireflection coatings of various designs, material combinations, and deposition temperatures are presented. The most significant effects are observed for overcoat layers on high reflectors and undercoat layers on antireflection coatings. Thresholds >6 J/cm(2) for 20 nsec pulses were observed in both cases.
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