Recent developments in silica sol-gel antireflection (AR) coatings

Silica sol-gel anti-reflective (AR) coatings have been investigated with particular reference to their laser induced damage threshold (LIDT) when subjected to irradiation from a Nd pulse laser at 1064 nm. Coatings (whose thickness was optimized for minimum reflection at 1064 nm) were deposited by spinning silica sols (average particle size 15 nm) formed by the base (ammonium hydroxide) catalyzed hydrolysis/condensation of TEOS in ethanol. Addition of polyethyleneglycols (PEGs) increased the size of the colloidal silica particles and also induced some particle aggregation in the sol, unlike a similar chain length diol. Increases in the LIDT of the coatings possibly depend upon the impurity levels, the wettability of the substrate, and the presence of PEG. LIDT improvements may be obtained by control of substrate and coating surface wettability, hydrophilicity, and surface chemistry.