BK7 Windows/Rods

BK7 Windows/Rods
BK7 Windows/Rods BK7 Windows/Rods BK7 Windows/Rods

BK7 is borosilicate crown optical glass with 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 (uncoated or coated) in visible and IR.

Newlight Photonics offers circular/rectangular BK7 windows or rods with thickness from 0.15 mm to 150 mm. 

Various high quality HR, AR, and partial reflective coatings are available upon request.

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Part No. Aperture Thickness Coating Price Availability Add to Cart

Basic Properties of BK7 and N-BK7 Glass:


BK7, N-BK7
Transparency Range 360 - 2000 nm
Density 2.51 g/cm3
Coefficients (dn/dT)
2.3 x 10-6 /oC
Optical Homogeneity Δn < 10-6 /cm
Mohs Hardness  ~ 6 
Thermal Conductivity 1.1 W/m/K
Thermal Expansion
8 x 10-6 /K (BK7), 7.1 x 10-6 /K (N-BK7)
Sellmeier Equations
(λ in µm)
n2=1+1.03961λ2/(λ2- 0.0060007)+0.23179λ2/(λ2-0.020018)+1.01047λ2/(λ2-103.5600)
Wavelength(nm) Index of Refraction
400 1.5308
532 1.5194
632.8 1.5150
1064 1.5066

Transmission curve:
material-bk7.GIF (10870 bytes)



Specifications of BK7 Windows:

Dimension Tolerance: Diameter:  ± 0.1 mm,
± 0.1 mm (T=<5mm), +0.5/-0.1 mm (T>5mm) 
Clear Aperture: > 85%
Surface Quality: 20/10 Scratch and Dig
Parallelism: < 1 arc min
Flatness: λ/8 @ 632.8 nm for T>=2mm
Transmission Wavefront Distortion: < λ/8 @ 632.8 nm for T=<25mm 
< λ/8 @ 632.8 nm per 25mm for T>25mm
Bevel: < 0.25 mm X 45°

N-BK7, the ROHS version of standard BK7 may be used for the windows without notice.  N-BK7 will always be used for EU customers in compliance with the RoHS regulations. Please let us know if N-BK7 and BK7 have to be distinguished for your applications.


Various high quality HR, AR, Broadband AR (BBAR) and partial reflective (PR) coatings are also available upon request.

AR Coatings: R<0.2% at the central wavelength
HR Coatings: R>99.6% at the central wavelength
PR Coatings: R=3-95% at the specified wavelength
Broadband AR: R<1% over the specified range

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