BK7

BK7, SF11, LaSFN9, BaK1, and F2 are the most important optical and physical constants for Schott optical glass types. These types are used in most Dream Lasers simple lens products and prisms. The most commonly required chemical characteristics and mechanical constants, are listed. Further numerical data and a more detailed discussion of the various testing processes can be found in the Schott Optical Glass catalog.

BK7 is a borosilicate crown optical glass with high homogeneity and low bubble and inclusion content. Its good physical and chemical properties make it widely used in visible and NIR windows, lenses and prisms.

BK7 Constants
Abbé Constant
64.17
Density
2.51 g/cm-3
Young's Modulus
8.20 x 109 dynes/mm2
Poisson's Ratio
0.206
Coefficient of Thermal Expansion (-30° to +70°C)
7.1 x 10-6/°C
Coefficient of Thermal Expansion (20° to 3000°C)
8.3 x 10-6/°C
Stress Birefringence, (Yellow Light)
10 nm/cm
Homogeneity within Melt
±1x10-4
Striae Grade (MIL-G-174-A)
A
Transformation Temperature
557°C
Climate Resistance
2
Stain Resistance
0
Acid Resistance
1.0
Alkali Resistance
2.0
Phosphate Resistance
2.3
Knoop Hardness
610
Dispersion Constants
B1 = 1.03961212 
B2 = 2.31792344x10-1 
B3 = 1.01046945
C1 = 6.00069867x10-3 
C2 = 2.00179144x10-2 
C3 = 1.03560653x102

The external transmittance of BK7 is shown in the figure below:

External transmission for 10-mm-thick BK7 glass