Introduction to BK7 Windows
BK7 (domestic equivalent grade K9/H-K9L) is a borosilicate crown optical glass, renowned for its balanced overall performance and moderate cost, making it one of the most commonly used window materials.

1. Optical Characteristics
   ? Transmission Range: 380 nm – 1.5 μm, with over 92% transmission in the visible to near-infrared region; can reach ≥98% with anti-reflection coating on both sides.
   ? Refractive Index: nd=1.5168, Abbe number νd≈64, low dispersion, and minimal imaging distortion.
   ? High material purity, very few bubbles or impurities, and excellent refractive index uniformity.

2. Physical/Mechanical Properties
   ? Density: 2.51 g cm?3; Knoop hardness: 610, offering good scratch resistance.
   ? Linear expansion coefficient ≈7×10?? K?1, with thermal stability superior to ordinary glass, suitable for long-term use in environments ranging from ?40 ℃ to +100 ℃.
   ? Strong chemical corrosion resistance, not prone to deliquescence, and can be cut, ground, and highly polished without special pretreatment.

3. Processing and Specifications
   ? Can be polished to surface quality 10-5, surface figure λ/10, parallelism <5″, and shaped into circular, square, or custom forms.
   ? Standard thickness ranges from 0.5-25 mm, with sizes from a few millimeters to over ?200 mm available for quick delivery.

4. Typical Applications
   ? Laser Systems: Resonator mirrors, output windows, protective windows.
   ? Imaging Equipment: CCD/CMOS camera lenses, microscopes, spectrometer windows.
   ? Medical and Detection: Endoscopes, gas detection, biochemical analyzers.
   ? Industrial and Aerospace: Sensors, rangefinders, aerospace optical instruments.