Antireflection coating of diamond elements of power optics for CO2 lasers

A technology of deposition of a single-layer PbF₂ coating, antireflecting for the CO₂ laser radiation, on diamond substrates is developed. As substrates, use is made of plates of polycrystalline CVD diamond. The transmission coefficient of diamond plates with two-side coating attains 98.5% – 99%. The measured laser-induced damage threshold of such plates under normal environment conditions for the pulsed (τ ~100 ns) and continuous-wave radiation of CO₂ lasers amounts to 250 and 4 MW cm^-2, respectively. These values are comparable with the thresholds of the diamond substrate damage. The increase in the damage threshold of the AR coating under continuous-wave irradiation to 5.5 MW cm^-2 is found in the case of preliminary multiple irradiation of samples by weaker laser pulses. This effect can be explained by the pollutant removal from the surface of the film without its damage (laser cleaning effect).