BK7 is borosilicate crown optical glass. It has an excellent physical and chemical properties for applications in visible and near IR. Large BK7 glass with high homogeneity, low bubble and inclusion content can be produced at a large quantity and at low cost, making it the standard material for optical components in visible and IR. Various high quality HR, AR, and partial reflective coatings are available on BK7 faces.

This kind of windows is made from SCHOTT N-BK7 Glass, which has transparent range from 330-2100nm. The BK7 window has good performance over visible and near IR spectrum for most application. The refractive index is 1.5168 at 587.6nm
 

StandardSpecifications:

Material: BK7 grade A optical glass
Diameter Tolerance: +0.0, -0.1mm
Thickness Tolerance: ± 0.2mm
Clear Aperture> 85%
Parallelism<1 arc minute
Surface Quality: 60-40 scratch and dig
Flatness: λ/4 per 25mm @632.8nm
Wavefront Distortion: λ/4 per 25mm @632.8nm
Bevel: 0.25mm x 45°
Other specification and coating are available upon request.