Sapphire Optical Windows

Name: Sapphire Optical Windows
Brand: PhotonEdge

Key Specifications

Material	Single-crystal Sapphire (Al2O3)
Transmission Range	180 - 4,500 nm
Hardness	Mohs 9 (second only to diamond)
Refractive Index	no = 1.768, ne = 1.760 @ 587nm
Diameter Range	3mm - 150mm
Thickness Range	0.5mm - 25mm
Surface Quality	20-10 / 40-20 (MIL-PRF-13830B)
Surface Flatness	lambda/4 @ 632.8nm
Thermal Stability	Stable to 2000 degrees C in air
CTE	5.0 x 10^-6/K (perpendicular to c-axis)

Material Options

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

Sapphire (Al2O3) — Ultimate scratch resistance and chemical inertness. For harsh environments, high pressure, and abrasive conditions.
UV Fused Silica (Alternative) — Better UV transmission below 200nm. Lower hardness but more economical for non-abrasive applications.
ZnSe (IR Alternative) — Better transmission beyond 4.5um to 18um. Softer material - not suitable for abrasive environments.

Coating Options

Coatings are engineered around your specific wavelength and operating conditions.

BBAR VIS-NIR — R < 0.5% across 400-1700nm. Maximizes throughput for visible and NIR systems.
AR @ 1064nm — For Nd:YAG laser system viewports in harsh environments.
AR UV-VIS — R < 0.25% across 200-700nm. For UV-visible spectroscopy in demanding environments.
Uncoated — ~7% Fresnel loss per surface (due to high n=1.77). Acceptable for protective cover glass.

Manufacturing Tolerances

We optimize specifications to match your system requirements — not over-specify. Tighter tolerances increase cost without always improving system performance. 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 with full documentation including interferometer reports, spectral curves, surface quality images and dimensional data.

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

Applications

High-pressure vessel viewports
Abrasive environment protective windows
Watch crystals and display covers
Harsh chemical environment observation ports
Military and aerospace sensor windows
High-temperature furnace observation
Underwater optical system windows
Scratch-resistant optical covers

Engineering Considerations

Birefringence: Sapphire is birefringent (delta-n = 0.008). For polarized light systems, this can cause unwanted polarization rotation. Account for crystal axis orientation in your design. For unpolarized applications, birefringence is not a concern.

Machining difficulty: Sapphire's extreme hardness makes it more expensive to machine than BK7 or fused silica. Complex geometries (thin edges, small features) significantly increase cost. Keep designs as simple as possible.

Thermal shock: Despite high temperature capability, sapphire can crack under rapid temperature changes due to thermal stress. Specify gradual temperature transitions in your system design.

Is Sapphire the Right Window Material?

Sapphire offers unmatched hardness but at a premium. Confirm if the investment is justified.

Scratch Resistance

Your Need	This Material?	Note
Abrasive environment	Yes ✓	Sapphire Mohs 9 is ideal
Cleanroom / controlled	No	Fused silica is sufficient at lower cost

Wavelength

Your Need	This Material?	Note
Visible-NIR (200-4500nm)	Yes ✓	Sapphire has excellent clarity
Mid-IR beyond 4.5um	No	Use ZnSe or Ge

Pressure

Your Need	This Material?	Note
High-pressure viewport	Yes ✓	Sapphire strength is unmatched
Standard conditions	No	Fused silica or BK7 are more economical

Summary

Sapphire is right for extreme scratch resistance, high pressure, or harsh environments. For standard applications, fused silica or N-BK7 offer equivalent optical performance at lower cost.

Frequently Asked Questions

How does sapphire compare to glass in scratch resistance?

Sapphire (Mohs 9) is dramatically harder than any optical glass. BK7 is approximately Mohs 5-6. In practical terms, sapphire will resist scratching from sand, dust, and most industrial abrasives that would quickly fog a glass window.

Can sapphire windows be used in vacuum systems?

Yes. Sapphire is compatible with ultra-high vacuum (UHV) environments. Its low outgassing and chemical inertness make it suitable for semiconductor processing and space applications.

What is the maximum pressure differential a sapphire window can handle?

Depends on diameter, thickness, and edge condition. A 25mm diameter x 3mm thick sapphire window can typically withstand >50 bar differential pressure. Contact us with your specific pressure requirements for engineering review.

Related Products

Sapphire Windows Fused Silica Windows ZnSe Windows BK7 Windows

Related Technical Resources

→ 5 Key Specifications for Buying Optical Windows → Infrared Optical Materials Comparison