BK7 is the most widely used optical glass for visible and near-infrared applications. A borosilicate crown glass, BK7 offers excellent optical clarity, good homogeneity, and reasonable cost — making it the default choice for many general-purpose optical components.
Imaging lenses and objectives
Beam splitters and prisms
General-purpose windows
Spectrometer optics
Machine vision systems
| Property | Value |
|---|---|
| Coefficient of Thermal Expansion (CTE) | 7.1 × 10⁻⁶ /K |
| Thermal Conductivity | 1.13 W/m·K |
| dn/dT (Thermo-optic Coefficient) | 3 × 10⁻⁶ /K |
| Maximum Operating Temperature | ~450°C (annealing point 557°C) |
BK7 has relatively low thermal conductivity and moderate thermal expansion. Avoid rapid temperature changes to prevent thermal shock cracking.
Standard coating types available for this material. Custom coating designs available on request.
Easy to machine, good for complex geometries. Standard optical grinding and machining methods apply.
Excellent polishability, achieves low scatter surfaces. Standard optical polishing compounds work well.
Low moisture absorption, stable in normal laboratory and industrial environments. Avoid prolonged high humidity.
Low cost, widely available in large blanks and standard sizes. Short lead times from stock.
No single optical material is perfect for every application. Here are situations where BK7 Optical Glass may not be the best fit, and what to consider instead.
→ Consider: UV Fused Silica
BK7 absorbs strongly below 350nm. For UV applications, fused silica transmits down to ~180nm.
→ Consider: Borosilicate or Sapphire
BK7 has moderate thermal expansion (7.1 x 10⁻⁶/K). For thermal stability, fused silica or sapphire perform better.
→ Consider: UV Fused Silica
BK7 has a lower laser-induced damage threshold (LIDT) than fused silica. For high-power lasers, fused silica is the safer choice.
→ Consider: Germanium, ZnSe, or ZnS
BK7 only transmits to about 2μm. For infrared work beyond this range, consider IR-grade materials.
Browse our catalog of precision optical components available in BK7 Optical Glass
Consider fused silica for UV applications or when lower thermal expansion is needed. Consider sapphire for high-wear environments. BK7 is a general-purpose optical glass — cost-effective for visible-range optics where extreme thermal or chemical resistance is not required.
Send us your specifications. Our engineering team will review and respond with material and coating recommendations within 24 hours.
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