Development of high-power laser coatings

Laser resistance and stress-free mirrors, windows, polarizers, and beam splitters up to $400~\mathrm{mm} \times 400~\mathrm{mm} $ are required for the construction of the series SG facilities. In order to improve the coating quality, a program has been in place for the last ten years. For the small-aperture pick-off mirror, the laser-induced damage threshold (LIDT) is above $60~\mathrm{J} / {\mathrm{cm} }^{2} $ (1064 nm, 3 ns), and the reflected wavefront is less than $\lambda / 4~(\lambda = 633~\mathrm{nm} )$ . The Brewster-angle polarizing beam splitter ( $\Phi 50\times 10~\mathrm{mm} $ ) shows the best LIDT result, up to $29. 8~\mathrm{J} ~{\mathrm{cm} }^{- 2} $ (1064 nm, 10 ns) for a p-polarized wave in the 2012 damage competition of the XLIV Annual Boulder Damage Symposium. For the larger-aperture mirror and polarizer, the LIDT is above $23~\mathrm{J} ~{\mathrm{cm} }^{- 2} $ (1064 nm, 3 ns) and $14~\mathrm{J} ~{\mathrm{cm} }^{- 2} $ (1064 nm, 3 ns), respectively. The reflected wavefront is less than $\lambda / 3~(\lambda = 633~\mathrm{nm} )$ at the used angle.