Laser damage testing of coated reflectors at excimer laser wavelengths

An important parameter in the design of large scale ultraviolet lasers (such as those envisioned for Inertial Confinement Fusion and Molecular Laser Isotope Separation) is the resistance to optical damage of windows, AR coatings, and coated reflectors. The damage thresholds of a variety of 248 nm, and 351 nm reflectors were measured. The coatings were composed of quarterwave stacks of oxide and/or fluoride films deposited on Suprasil 2 substrates. Testing was accomplished at 35 Hz with nominal 10 as pulses focused to a mean 1/sq e diameter of 0.5 to 0.6 mm. Damage threshold (defined as the highest fluence at which 10/10 sites survived 1000 shots) ranged from 1 to 5 J/sq cm with a strong dependence upon laser wavelength and reflector coating materials.