BK7 windows

BK7 windows, made from high-quality Schott glass, are renowned for their excellent optical performance. These optical windows offer uniform transmission across the visible spectrum and extend into the near-infrared range. Featuring high refractive index homogeneity and a clear, colorless appearance, BK7 windows are a top choice for demanding optical applications.

Manufactured from Schott Optical borosilicate-crown glass, BK7 windows are free from bubbles or inclusions, ensuring high purity and clarity. With a density of 2.51 g/cm³ and a Knoop hardness of 610, BK7 glass is both durable and optically superior. The coefficient of thermal expansion is 7.1 x 10⁻⁶/K from -30°C to +70°C, and 8.3 x 10⁻⁶/K from +20°C to +300°C.

For applications requiring good UV transmission or a lower thermal expansion coefficient, UV fused silica windows may be more suitable. However, BK7 windows stand out for their high resistance to staining and acids, with an SR-class of 1. The AR-class for alkali resistance is slightly lower, rated at 2.

Key specifications for BK7 windows include a clear aperture greater than 85% of the diameter, with a diameter tolerance of +0.0/-0.05mm and a thickness tolerance of ±0.1mm.

Surface Quality of BK7 Windows

The surface quality of BK7 windows is essential for maintaining optical clarity. It is measured using scratch-dig numbers, as per U.S. Military Performance Specification MIL-PRF-13830B. The scratch number indicates the brightness, with 10 being the least bright and 80 the brightest. The dig number represents the size of the largest pit, calculated by measuring the diameter in hundredths of a millimeter.

Most applications only need a surface quality of 40-20, but laser applications demand 20-10 or better. BK7 windows from our factory meet a 10-5 scratch-dig standard, making them suitable for high-power laser applications with minimal wavefront distortion and light scatter. Wavefront distortion is controlled to λ/10 per 25mm.

Custom BK7 Windows and Coatings

We offer customization options for our BK7 windows, including anti-reflective (AR) coatings and protective bevels. We offer circular windows ranging from 3.5mm to 25.4mm in diameter and thicknesses between 1mm and 3mm. Square BK7 windows with similar specifications are also available.

Our advanced manufacturing capabilities allow us to meet custom optical requirements. Whether you need standard or custom BK7 windows, we ensure precision and high-quality performance for every application.

Standard Specifications :

• Material: BK7 Schott glass
• Irregularity: λ/10
• Diameter Tolerance: +0.0/-0.05mm
• Thickness Tolerance: ±0.1mm
• Clear Aperture: >85%
• Parallelism: 1 arc min
• Surface Quality: 10-5 scratch-dig
• Wavefront Distortion: λ/10 per 25mm

For inquiries or to discuss custom specifications, please contact our team. We specialize in producing high-precision optics, tailored to your optical system’s needs.