High Transmittance and Stable Optical Path BK7 Window

BK7 Windows are precision optical components made from high-quality BK7 glass, offering excellent transmission, low birefringence, and stable performance. Their versatility and durability make them ideal for demanding optical systems and integration into compact setups.

Feature:

High-transmission BK7 glass providing clarity across visible and near-infrared wavelengths
Low wavefront distortion and minimal birefringence for accurate beam propagation
Superior surface quality and polishing for reliable, stable optical performance
AR, HR, or custom coatings available to enhance system efficiency
Custom dimensions and edge designs for seamless integration into various optical assemblies

Application: Laser optics, imaging systems, spectroscopy, optical communication, aerospace, and precision instruments requiring reliable, high-performance optical windows.

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1. High-Purity Borosilicate Crown Glass

BK7 is a borosilicate crown glass composed primarily of SiO₂ (~70%), with sodium borate and sodium oxide. It offers:

Density: 2.51 g/cm³
Thermal Expansion Coefficient: 3.3×10⁻⁶/°C (20–300 °C)
Vickers Hardness: HV 560, better scratch resistance than ordinary glass
This ensures good thermal and mechanical stability, essential for long-term optical applications.

2. Optical Properties for Broadband Transmission

Wavelength Range: 350 nm – 2100 nm
Typical Transmission: >91% at 589 nm (uncoated), and >99% with AR coatings
Refractive Index: n_D = 1.5168
Abbe Number: ν_D = 64.1 (low chromatic dispersion)
These properties make BK7 suitable for systems that do not require dispersion correction but demand high clarity and broadband performance.

3. Precision Manufacturing and Structural Flexibility

Geometry: Flat parallel BK7 windows with thickness from 1 mm to 20 mm, diameters or side lengths from 1 mm to 300 mm
Flatness: Up to λ/10 for high-precision optics
Customization: Available in circular, square, or special shapes, with optional beveling or apertures
Surface Quality: Polished to <1 nm RMS roughness for high-power laser or imaging use

4. Versatile Applications

Optical Instruments & Imaging

Lens protection in cameras, telescopes, and microscopes
Substrates for beamsplitters or interference filters

Laser and Fiber Optics

Protective BK7 windows in CO₂ lasers, fiber modules (e.g., 1310/1550 nm)
Components in beam shaping systems

Industrial & Environmental Sensing

BK7 Front windows for IR sensors, analyzers, or machine vision cameras
Weather-resistant and oil-resistant viewing windows

Scientific Research

Flat windows for interferometers, spectrometers, and LIBS systems
Spectroscopic reference and sample windows

Consumer Electronics

Cover glass for premium touchscreens and optical modules in AR/VR
Highly visible transmittance substrates with optional IR reflection coatings

5. BK7 Window Selection Guidelines

UV or IR Range Needs:

For <350 nm: use fused silica;
For >2100 nm: use germanium or silicon

Flatness & Surface Quality:

λ/10 or better for high-end imaging
Surface roughness <1 nm for laser compatibility

Coating Considerations:

Apply AR coating to boost transmission and reduce reflections
Use high-damage-threshold coatings for high-power laser applications

Parameter	Specification
Material	Schott BK7 or equivalent borosilicate crown glass
Wavelength Range	350 – 2100 nm
Transmittance	>91% at 589 nm (uncoated); >99% with broadband AR coating
Refractive Index (n_D)	1.5168
Abbe Number (ν_D)	64.1 (low dispersion)
Flatness	λ/10, λ/4, or λ/2 @ 633 nm (application dependent)
Surface Quality	20/10, 40/20, or 60/40 (per MIL or ISO 10110 standards)
Surface Roughness	<1 nm RMS for laser applications
Thickness	0.1 mm – 20 mm
Dimension Tolerance	+0.0 / –0.1 mm (standard); tighter tolerances on request
Shape Options	Circular, square, rectangular, or custom cut
Edge Finish	Ground, beveled, or polished
Coating Options	Uncoated, AR/VIS/NIR/IR coatings, high-damage-threshold coatings
Operating Temp. Range	–40°C to +300°C