Sapphire windows from Laser Research Optics are available at sizes from 1/2 to 2 in.

Sapphire fiber laser windows for 1064 nm cutting lasers have Moh 9 hardness with antireflective coatings on both sides, for transmission of >99.5% at 1.06 μm and >90% between 650 and 670 nm. They have a 10-5 scratch-dig finish, provide 1/4-wave transmitted wavefront, and are available at sizes from 1/2 to 2 in.
Laser Research Optics
Providence, RI
www.laserresearchoptics.net