Avantier’s BK7 windows are ideally suited for rigorous optical applications, attainable with laser-grade precision. BK7 glass boasts a density of 2.51 g/cm³ and a Knoop hardness rating of 610. Its coefficient of thermal expansion measures approximately 7.1 x 10^-6 K in the range from -30 °C to +70 °C, and about 8.3 x 10^-6/K from +20 °C to +300 °C.

Surface Quality Specifications for BK7 Windows

The surface quality of our optical windows is determined using a two-part scratch dig number system, in accordance with U.S. Military Performance Specification MIL-PRF-13830B. The first number characterizes the brightness of scratches, denoted as 10, 20, 40, 60, or 80, with higher values indicating more pronounced scratch brightness. These are calibrated by comparison with reference scratches.

For most applications, standard quality falls within the 40-20 range, while laser applications demand a minimum surface quality of 20-10. Our BK7 windows adhere to a factory standard of 10-5 scratch dig, signifying precision laser quality. This ensures their suitability even for high-power or UV laser applications. The high surface quality also minimizes wavefront distortion and light scattering when optical radiation passes through our windows. According to our factory standards, the maximum allowable wavefront distortion is λ/10 per 25mm.

Customization Options

Our BK7 windows are available with or without anti-reflective (AR) coatings, and an optional protective bevel. We maintain a stock of circular windows ranging from 3.5 to 25.4 mm in diameter and 1-3 mm in thickness. Additionally, square BK7 windows with similar dimensions can be accommodated.

Factory Standard