Laser damage in porous-silica antireflection films

Controlled 355-nm, 0.6-ns pulses were used to measure laser-damage thresholds of porous-silica antireflection coatings deposited from a polymer solution onto fused silica substrates. For 118 coatings with optical thickness of 500 to 600 nm, the median threshold was less than 2 J/cm(2), and thresholds were not systematically dependent on either the level of filtration of the coating solution or the procedure used to clean the substrates. For coatings 87 to 90 nm in optical thickness, thresholds were as large as 9 J/cm(2), which is the threshold of the bare polished surfaces of the fused silica substrates. The data suggests that carbon residues from the coating solution are responsible for damage in the thicker coatings.