Lens Savers® Premium grade protection windows are suitable for most YAG applications.  Windows are available with and without anti-reflective (AR) coatings.  Uncoated windows will transmit 92% of the available energy at 1.064 microns.  Coated windows transmit in excess of 99% of available energy at 1.064 microns. 
Material: BK-7
Tolerances - Diameter +0.00/-0.25mm/Thickness +0.00/-0.25mm
Flatness: 1/5 wave per inch at 632.8nm over clear aperture
Parallelism: Less than 3 arc min
Surface: 60-40
Clear aperture: 90% of diameter
AR coating: Less than 0.5% reflection/side 1064nm