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.

A “dig,” which represents a pit or small crater on the glass surface, is defined by its diameter. The dig number corresponds to the actual size of the largest permissible dig, specified in hundredths of a millimeter. In cases of irregularly shaped digs, the diameter is calculated as half of the length + width.

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.

Our dedicated design team is ready to assist you at every stage of your optical system design. Please feel free to reach out for a complimentary consultation and to discuss any specific custom requirements you may have. Our cutting-edge machinery and metrology equipment enable us to produce precise, high-quality optics tailored to your unique application.

Factory Standard