Custom Fused Silica Optical Windows

UV-grade fused silica optical windows engineered for demanding applications from deep UV to near-infrared. High laser damage threshold, excellent thermal stability and superior surface quality for laser systems, semiconductor equipment and scientific instruments.

Key Specifications

Material	UV Fused Silica (SiO₂)
Transmission Range	185 – 2,500 nm
Diameter Range	Custom / 3mm – 200mm
Thickness Range	Custom / 0.5mm – 50mm
Surface Quality	10-5 / 20-10 / 40-20 (MIL-PRF-13830B)
Surface Flatness	λ/10 / λ/20 per inch @ 632.8nm
Coating	AR / HR / BBAR / Custom
Clear Aperture	≥90%
Parallelism	< 3 arc-sec (precision) / < 1 arc-min (standard)
LIDT	> 10 J/cm² @ 1064nm, 10ns (AR coated)

Material Options

Select the optimal optical material based on your wavelength, power, thermal environment and mechanical requirements.

UV Grade Fused Silica — High OH content, excellent UV transmission down to 185nm. Ideal for excimer lasers and UV lithography.
N-BK7 — Cost-effective for visible-NIR applications. Good optical homogeneity for general-purpose windows.
CaF₂ (Calcium Fluoride) — Broad UV-IR transmission (130nm–10µm). Low refractive index, excellent for fluorescence and Raman spectroscopy.
Sapphire (Al₂O₃) — Extreme hardness (Mohs 9). Survives high-pressure and high-temperature environments. 150–5500nm transmission.

Available Optical Materials

Select the optimal substrate material based on your wavelength, environment, and budget requirements.

Material	Transmission	Key Advantage	Considerations
UV Fused Silica	UV / VIS / NIR (185-2100nm)	Excellent UV transmission, high laser damage threshold	Higher cost than BK7
N-BK7	VIS / NIR (350-2000nm)	General-purpose, low cost, good homogeneity	Not suitable for UV < 350nm
Sapphire	UV / VIS / NIR (150-5500nm)	Extremely hard (9H), scratch resistant	Birefringent, higher refractive index
CaF₂ (Calcium Fluoride)	Deep UV / VIS / IR (130-7800nm)	Broadest transmission range, low refractive index	Fragile, hygroscopic, higher cost

Not sure which material to choose?

Ask AI Optical Engineer

Coating Options

Coatings are engineered around your specific wavelength and operating conditions.

Broadband AR (UV-VIS) — R < 0.25% per surface, 193–700nm. Maximizes throughput for multi-wavelength systems.
V-band AR (355nm) — R < 0.1% @ 355nm. Optimized for Nd:YAG third harmonic laser systems.
BBAR (Broadband) — R < 0.5% across 350–2000nm. Single coating for wide spectral coverage.
Uncoated — Suitable for low-power applications or where coating absorption is a concern. ~4% Fresnel loss per surface.
Custom coating — Design your coating for specific wavelength, angle of incidence and polarization requirements.

Manufacturing Tolerances

We optimize specifications to match your system requirements — not over-specify. Tighter tolerances increase cost without always improving system performance. Our engineers will work with you to identify which parameters actually matter for your application and where standard tolerances are sufficient. Typical manufacturing capabilities:

Surface quality: from 60-40 to 10-5 scratch-dig
Surface flatness: from λ/4 to λ/20 per inch
Dimensional tolerance: ±0.01mm to ±0.05mm
Centration: <3 arc min standard, <30 arc sec precision

Inspection & Quality

Every component undergoes 100% inspection before shipment. We provide full inspection documentation including interferometer reports, spectral transmission curves, surface quality images and dimensional measurement data. Equipment capabilities:

Laser interferometry: λ/100 resolution for flatness and wavefront
Spectrophotometry: 190nm – 25μm transmission and reflection
Surface inspection: MIL-PRF-13830B compliant
Dimensional metrology: ±0.01mm accuracy

Applications

UV laser systems (193nm, 266nm, 355nm)
Semiconductor inspection and lithography equipment
Spectroscopy and analytical instruments
Medical imaging and diagnostic devices
Vacuum and cryogenic system viewports
High-power laser beam paths

Engineering Considerations

Thermal management: Fused silica has near-zero thermal expansion (CTE ≈ 0.55 × 10⁻⁶/K), making it ideal for environments with temperature variation. However, at high average powers, even small absorption in coatings can cause thermal lensing.

LIDT considerations: Always specify your laser wavelength, pulse duration, repetition rate and beam diameter. Laser-induced damage threshold depends on all of these. A coating optimized for 355nm CW may fail at 355nm pulsed.

Surface quality vs. cost: 10-5 scratch-dig is needed for high-precision imaging and laser cavities. For simple protective windows, 60-40 is sufficient and significantly less expensive.

Wedging: For laser cavity windows, specify wedged windows (typically 0.5°–3°) to eliminate etalon effects that cause power instability.

Is Fused Silica the Right Window Material for Your System?

Use this quick decision guide to confirm whether fused silica is optimal, or whether you should consider an alternative material.

Wavelength

Your Requirement	Best Material	Why
Need UV transmission (< 350nm)	Fused Silica ✓	Fused silica transmits down to 185nm. Ideal for UV.
Visible-NIR only (350-2000nm)	Nbk7	N-BK7 is more economical for visible-NIR. No need to pay for UV capability.
Need IR beyond 4.5um	Znse	Fused silica cuts off at 2.5um. Use ZnSe for mid-IR or LWIR applications.

Laser Power

Your Requirement	Best Material	Why
High-power laser (> 50W CW)	Fused Silica ✓	Low thermal expansion and high LIDT make fused silica the standard for high-power laser windows.
Low-power or non-laser	Nbk7	For non-laser or low-power applications, N-BK7 provides adequate performance at lower cost.

Environment

Your Requirement	Best Material	Why
Extreme scratch resistance needed	Sapphire	If the window will be exposed to abrasive particles or frequent cleaning, sapphire (Mohs 9) outperforms all glass.
Standard indoor/cleanroom	Fused Silica ✓	For controlled environments, fused silica provides excellent performance without the premium cost of sapphire.

Summary

Fused silica is the right choice when you need UV transmission, high-power laser compatibility, or low thermal expansion. For visible-only or budget applications, consider N-BK7. For extreme durability, choose sapphire.

Engineering Documentation

The following documentation is available upon request for qualified engineering projects:

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Dimensional Drawing

CAD & dimensional specs per your requirements

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Material Data Sheet

Material properties, transmission curves & certificates

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Coating Performance Curve

Spectrophotometric measurement data

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Inspection Report

Surface quality, flatness, centration & dimensional data

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Certificate of Conformance

CoC with full traceability per project requirements

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Custom Specification Sheet

Application-specific specification documentation

Documentation availability depends on project scope and order quantity. Request details during RFQ.

Frequently Asked Questions

What is the difference between UV fused silica and N-BK7 for optical windows?

UV fused silica transmits from 185nm with high laser damage threshold and near-zero thermal expansion. N-BK7 is more economical for visible-NIR applications but absorbs below 350nm and has higher thermal expansion. For UV laser systems or high-power applications, fused silica is the standard choice.

What surface quality should I specify for my window?

For laser cavity windows and precision imaging: 10-5. For general beam paths and protective windows: 40-20 or 60-40 is sufficient. Tighter surface quality increases cost significantly, so specify only what your system actually requires.

Can you provide windows with custom dimensions?

Yes. We manufacture custom optical windows to your exact specifications including diameter, thickness, wedge angle, edge profile and coating. Typical lead time for custom windows is 2–4 weeks depending on complexity and quantity.

What is the laser damage threshold of your AR-coated fused silica windows?

Typical LIDT for our UV BBAR coated fused silica windows is >10 J/cm² at 1064nm (10ns pulse). For specific wavelengths and pulse parameters, we provide measured LIDT data per ISO 21254. Contact us with your laser parameters for exact specifications.