Which Optical Window Material Should You Use? (Sapphire vs CaF₂ vs BK7 vs Fused Silica)
- martin14662
- 4 days ago
- 2 min read
Choosing the correct optical window material is critical to the performance of any optical system. Different materials offer very different properties in terms of strength, transmission range, cost and environmental resistance.
This guide provides a practical comparison of the most commonly used optical window materials, helping you select the right option based on your application.
If you already have a drawing or specification, you can also 👉 upload it here for a quotation.
WHAT AFFECTS MATERIAL SELECTION
The correct optical window material depends on several key factors:
Wavelength range (UV, visible, infrared)
Mechanical strength requirements
Environmental conditions (pressure, abrasion, temperature)
Cost constraints
Understanding these factors will help you narrow down the most suitable material.
SAPPHIRE OPTICAL WINDOWS
Sapphire is typically used where strength and durability are critical.
Best for:
High pressure environments
Abrasive or harsh conditions
Applications requiring extreme durability
Key advantages:
Very high mechanical strength
Excellent scratch resistance
Wide transmission range
Limitations:
Higher cost
Not always necessary for standard applications
Sapphire Window Assembly
CaF₂ OPTICAL WINDOWS
Calcium Fluoride (CaF₂) is commonly used in infrared and thermal imaging systems.
Best for:
Infrared optical systems
Thermal imaging applications
Wide wavelength transmission
Key advantages:
Excellent transmission from UV to IR
Low absorption in infrared
Limitations:
Lower mechanical strength than sapphire
Less suitable for harsh environments
FUSED SILICA OPTICAL WINDOWS
Fused silica is widely used in precision optical and laser systems.
Best for:
UV optical applications
Laser systems
Precision optical systems
Key advantages:
Excellent optical clarity
Low thermal expansion
Stable in precision applications
Limitations:
Not ideal for infrared applications
Lower strength than sapphire
BK7 OPTICAL WINDOWS
BK7 is one of the most commonly used optical glass materials and is typically the default choice for general applications.
Best for:
General optical systems
Visible light applications
Cost-sensitive projects
Key advantages:
Cost-effective
Good optical performance in visible wavelengths
Widely available
Limitations:
Not suitable for infrared applications
Lower durability compared to sapphire
QUICK COMPARISON
Material | Best For | Strength | IR Use | Cost |
Sapphire | Harsh environments | High | Medium | High |
CaF₂ | IR / thermal | Low | High | Medium |
Fused Silica | UV / precision | Medium | Low | Medium |
BK7 | General applications | Low | Low | Low |
Infrared Silicon Windows
APPLICATION-BASED GUIDANCE
If you are selecting based on application:
Thermal imaging systems → CaF₂, ZnSe, Silicon
High pressure environments → Sapphire
Laser and UV systems → Fused Silica
General optical use → BK7
STILL NOT SURE?
If you are unsure which material to choose:
ABOUT OUR SUPPLY
Global Optics supplies custom optical windows manufactured exactly to customer drawings and specifications.
No minimum order quantity
One-off prototypes to production supply
UK inspection prior to dispatch