BK7 Window

BK7 and N-BK7( a RoHS-compliant form of BK7) are high quality optical glass commonly used for windows, lenses, and prisms where transmission in the range 0.4µm to 1.4µm is desired. It is used for thermally non-critical applications. It has excellent mechanical and optical properties.

Transmission Range : 0.12 to 7 µm
Refractive Index : No 1.413 at 0.22 µm
Absorption Coefficient : 40 x 10-3 cm-1 at 2.7 µm
Reststrahlen Peak : 20 µm (1)
dn/dT : 2.3 (para) 1.7 (perp) at 0.4 µm (1)
dn/dµ = 0 : 1.4 µm
Density : 3.18g/cc
Melting Point : 1255°C
Thermal Conductivity : 21 (para) 33.6 (perp) W m-1 K-1 at 300K
Thermal Expansion : 13.7 (para) 8.9 (perp) x 10-6 /K
Hardness : Knoop 415
Specific Heat Capacity : 1003 J Kg m-1 K-1
Dielectric Constant : 4.87 (para) 5.45 (perp) at 1MHz
Youngs Modulus (E) : 138 GPa
Shear Modulus (G) : 54.66GPa
Bulk Modulus (K) : 101.32 GPa
Elastic Coefficients : C11=140 C12=89 C44=57 C13=63 C66=96 (2)
Apparent Elastic Limit : 49.6 GPa (7200 psi)
Poisson Ratio : 0.276 (2)
Solubility : 0.0002g/100g water
Molecular Weight : 62.32
Class/Structure : Tetragonal, can cleave on c-axis

Application:

• Precision & Laser Window
• Mirror Substrate
• Brewster Window
• Round Wedge

Specifications:

Diameter Tolerance: +0.00/-0.1 mm
Thickness Tolerance: +0.0/-0.2mm
Parallelism: <10", <1' or 30', 2°, 4°, 6°, 8°, 10° Wedge
Surface Quality: 10-5, 20-10 or 60-40
Clear Aperture: 90% of diameter
Wavefront Distortion: λ/4 or λ/10
Bevel: 0.25mm @45°
Coating: Available upon request