Development of high-power laser coatings

Laser resistance and stress-free mirrors, windows, polarizers, and beam splitters up to 400 mm × 400 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 J/cm2 (1064 nm, 3 ns), and the reflected wavefront is less than λ/4 (λ= 633 nm). The Brewster-angle polarizing beam splitter (Φ50 × 10 mm) shows the best LIDT result, up to 29.8 J 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 J cm−2 (1064 nm, 3 ns) and 14 J cm−2 (1064 nm, 3 ns), respectively. The reflected wavefront is less than λ/3 (λ= 633 nm) at the used angle.