When the broadest transmission spectrum is required (from 185nm to 2000nm) together with high durability, all for reasonable cost , these windows are ideal.
　

Material: UV quality fused silica
Refractive index: 1.46 @600nm
Diameter: +0 -0.2mm
Substrate flatness: λ/10 or λ/4
Parallelism: 5arcses or 3arcmin
Bevel: 0.2mm X 45º
Surface Quality: 40-20
Both side polished

     Square or Rectangle is available.