Borofloat 33 vs Fused Silica Laser Mirrors
By Esco Optics, Inc. | Published: 2026-10-21
Category: Comparisons
Compare Borofloat 33 and fused silica laser mirror substrates for 488 nm and 633 nm applications. Understand thermal, cost, and reflectivity trade-offs.
Quick answer
Choose Borofloat 33 for cost-sensitive visible laser setups where thermal drift is minimal; choose fused silica for UV or high-power applications requiring superior thermal stability and lower expansion.
Thermal expansion and stability
Fused silica has a coefficient of thermal expansion (CTE) roughly 5 times lower than Borofloat 33. This makes fused silica the clear choice when the laser mirror will experience temperature changes or high average power, as it maintains optical alignment and surface figure. Borofloat 33 is adequate for stable, low-power environments and costs significantly less.
Reflectivity and coating compatibility
Both substrates can be coated with narrowband Maximum Reflecting (MAX R) coatings. The Esco Optics Borofloat 33 mirrors for 488–514.5 nm and 633 nm offer nearly complete reflection over their specified ranges with negligible absorption. Fused silica substrates accept the same coatings, but their lower thermal expansion reduces coating stress and risk of delamination under thermal cycling. The trade-off is higher substrate cost for fused silica.
Wavelength range and application fit
Borofloat 33 transmits well from the visible into the near-IR, making it suitable for common laser lines like 488 nm, 514.5 nm, and 633 nm. Fused silica extends into the UV and deep UV, so if your laser operates below 350 nm, fused silica is necessary. For visible-only systems, Borofloat 33 offers a practical, lower-cost alternative without sacrificing reflectivity performance.
Trade-offs at a glance
- Borofloat 33 thermal stability: CTE ~3.3 ppm/K; acceptable for stable lab environments but can cause beam drift under thermal load. Use fused silica if your laser runs >5W or ambient temperature fluctuates more than ±2°C.
- Fused silica cost vs. performance: Fused silica costs 2–4× more per mirror than Borofloat 33 but offers 5× lower CTE and UV transmission. Budget for fused silica only when thermal stability or UV capability is essential.
- Coating reflectivity vs. bandwidth: MAX R coatings achieve >99% reflectivity over a narrow band; metal mirrors offer broader bandwidth but lower peak reflectivity. Stick with MAX R for single-line lasers; consider metal mirrors if you switch wavelengths frequently.
Product facts
- Borofloat 33 Mirror, MAX R 488nm-514.5nm: Narrowband Maximum Reflecting Coating (MAX R) for 488–514.5 nm, nearly complete reflection, negligible absorption, meets MIL durability standards. Ideal for argon-ion and similar visible lasers; the coating's high reflectivity maximizes output but increases polarization sensitivity.
Borofloat 33 Mirror, MAX R 488nm-514.5nm - Borofloat 33 Mirror, MAX R 633 nm: Narrowband Maximum Reflecting Coating (MAX R) for 633 nm, nearly complete reflection, negligible absorption, meets MIL durability standards. Perfect for HeNe lasers and other 633 nm sources; the narrowband design delivers peak performance at that wavelength at a higher cost than broadband metal mirrors.
Borofloat 33 Mirror, MAX R 633 nm
Which substrate fits your setup?
Best for
- Cost-conscious visible laser setups (488 nm, 514.5 nm, 633 nm) with stable temperatures
- HeNe or argon-ion laser systems where thermal drift is not a concern
Not for
- UV laser applications below 350 nm
- High-power lasers or environments with significant temperature changes
