Borosilicate Crown Glass (BK7)

Material
BK7

 

The Borosilicate Crown Optical Glass is the most used technical optical glass for high quality optical components in the visible and near IR range. It possesses the high linear optical transmission in the visible range and down to 350nm in the ultraviolet. BK7 has a high homogeneity with a very low number of inclusions and is almost bubble-free. Its appearance is very clear and colorless. BK7 is relatively hard and shows a good scratch resistance. The chemical properties of BK7 are very stable, that's why special treatment to grind and polish isn't required, thus reducing manufacturing costs.

 

BK7 is widely used for production of windows, prisms, lenses, mirror, substrates and other optical items.

Properties
Optical properties
Transmission range
330‐2100
Refractive index @587,6 nm
nd = 1.51680
Refractive index @546,07 nm
ne = 1.51872
Reflection losses, % for two surfaces
8,3 @588 nm
Physical properties
Density in g/cm3
2,51 @20°C
Abbe Constant
nd = 64.17

ne = 63.93

Principal dispersion
nF ‐ nC = 0,008054

nF‘ ‐ nC‘ = 0,008110

Thermal conductivity in W/(m · K)
1,114
Thermal expansion in 1/K
7,1 · 10-6 (-30/+70°C)

8,3 · 10-6 (20/300°C)

Transformation temperature
557
Specific heat capacity, J/(kg/K)
858
Young's Modulus (E) in N/mm2
82·103
Poisson's ratio
0,206
Optical stress coefficient, mm2/N
2,77·10-6
Knoop Hardness , kg/mm2
610
Stain resistance class
0
Climatic resistance class
2
Acid resistance class
1
Alkali resistance class
2
Phosphate resistance class
2,3
Spectral properties
sample thickness: 10 mm