BK7 vs Fused Silica: Which Material Should You Choose?
optical material choise
6/1/20261 min read
When designing an optical system, one of the first questions you'll face is: which material should I use for my lenses or windows? Two of the most common choices are BK7 and Fused Silica. Understanding their differences can save time, money, and performance headaches.
What is BK7?
BK7 is a borosilicate crown glass commonly used in optical components. It is widely appreciated for:
Good optical clarity in the visible spectrum (400–700 nm)
Low cost and wide availability
Ease of manufacturing, including polishing and coating
Moderate thermal expansion, suitable for most general applications
Typical applications:
Imaging systems
Laser pointers and markers (low-power)
Sensors
Windows and lenses for visible light
Limitations:
Poor UV transmission below 350 nm
Lower laser damage threshold compared to fused silica
Less suitable for high-power laser applications
What is Fused Silica?
Fused Silica (also called synthetic quartz) is a high-purity silica glass with superior optical and thermal properties:
Excellent transmission from UV to near-IR (200–2500 nm)
Very low thermal expansion, ideal for high-power lasers and precise optics
High laser-induced damage threshold (LIDT), can handle high-intensity laser applications
Outstanding chemical and thermal stability
Typical applications:
High-power laser systems
UV optics
Semiconductor lithography
Scientific and research instrumentation
Space optics and aerospace applications
Limitations:
Higher cost
Harder to process and polish compared to BK7
Quick Comparison Table
Property BK7 Fused Silica
Spectral Range 350–2000 nm 200–2500 nm
Laser Damage Threshold Low High
Thermal Expansion Moderate Very low
Cost Affordable Expensive
Typical Use Visible optics, imaging High-power laser, UV optics, precision instruments
How to Choose?
If your project is general visible-light imaging: BK7 is usually sufficient and cost-effective.
If your project involves UV, high-power lasers, or precision optics: Fused Silica is the safer and more reliable choice.
Consider the environment: Fused Silica performs better under thermal stress and in harsh conditions.
Bottom line: Both BK7 and Fused Silica have their place. Your choice should depend on wavelength, laser power, precision, and budget. Understanding these differences early can prevent costly mistakes in optical design.
For more information, please feel free to contact info@positiveoptic.com
#Optics #Photonics #LaserOptics #OpticalMaterials #BK7 #FusedSilica #PrecisionOptics #CustomOptics