Borofloat 33 Laser Mirror: Key Specs and Buying Considerations
By Esco Optics, Inc. | Published: 2026-10-23
Category: Buying Guides
Learn the key specifications of Borofloat 33 laser mirrors with Al-MgF2 coating, how they compare to fused silica, and when to choose them for your laser setup.
Quick Answer
Choose a Borofloat 33 laser mirror when you need an affordable, low-thermal-expansion substrate for broadband visible and near-IR applications, but consider fused silica if your setup demands deep-UV performance or extreme thermal stability.
Why Substrate Choice Matters
The mirror substrate directly affects how your optic handles heat, transmits wavelength-specific energy, and maintains surface figure under stress. Borofloat 33 offers a balanced middle ground between cost and performance for many laser applications.
Understanding your laser's wavelength, power density, and operating environment is the first step to picking the right mirror. The substrate's coefficient of thermal expansion (CTE) and internal homogeneity will influence beam quality over time.
Comparing Borofloat 33 and Fused Silica
Borofloat 33 provides lower thermal expansion than standard glass (CTE ~3.3 ppm/K), which reduces focus shift during warm-up. It is also more cost-effective than fused silica, making it a common choice for general lab lasers and industrial marking systems.
Fused silica excels in deep-UV (193 nm) and high-power-IR applications due to its near-zero thermal expansion and superior transmission in those ranges. If your laser operates below 300 nm, fused silica is the safer choice despite its higher price.
Understanding the Al-MgF2 Coating
The aluminum coating with a magnesium fluoride overcoat provides high reflectance across a wide spectrum (approximately 90%+ from 400 nm to 2 μm). This protective layer also resists oxidation and minor handling scratches better than bare aluminum alone.
However, Al-MgF2 coatings typically have lower damage thresholds than dielectric stacks. For high-peak-power pulsed lasers (nanosecond pulses >1 J/cm²), consider dielectric-coated mirrors instead.
Decision Rules for Choosing a Borofloat 33 Laser Mirror
- Match Wavelength to Coating: Al-MgF2 works well from 400 nm to 2 μm. For UV lasers below 350 nm or high-power IR above 2 μm, choose a dielectric-coated mirror instead.
- Check Surface Accuracy: Specify surface accuracy (λ/4, λ/10, or λ/20) based on your beam collimation and wavefront error requirements. Higher accuracy increases cost but improves performance for interferometry or Gaussian beams. For basic beam steering, λ/4 is often sufficient.
- Consider Thermal Drift: Borofloat 33's CTE of ~3.3 ppm/K is good for many labs but not stable enough for high-power CW lasers (over 100 W) without active cooling. Fused silica is better for high-heat applications. If your laser runs continuously above 100 W, test thermal stability with a mock run.
- Evaluate Lifetime and Cleaning: The MgF2 overcoat makes cleaning easier than bare aluminum, but avoid abrasive wipes. Use lens paper with acetone or isopropyl alcohol. Plan to replace mirrors after several cleaning cycles.
- Budget vs Performance: Borofloat 33 mirrors cost roughly 30–50% less than equivalent fused silica mirrors. If your application does not require deep-UV or ultra-low expansion, the savings can be put toward other optics. Calculate total system cost including mounts and reflectivity losses.
Product Spotlight
- Borofloat 33 Laser Mirror, Al-MgF2 Coated: Manufactured from Borofloat 33 with a front surface Al-MgF2 coating for broadband reflectance. This makes it a versatile, affordable choice for visible and near-IR laser setups where UV or extreme power handling is not required.
Borofloat 33 Laser Mirror, Al-MgF2 Coated
Ideal User Profile
Best For
- General-purpose laser beam steering in visible and near-IR (400–2000 nm)
- Budget-conscious labs and small-scale industrial systems
- Applications requiring moderate thermal stability without high-power extremes
Not For
- Deep-UV laser systems (193–350 nm) — choose fused silica
- High-power pulsed lasers needing >1 J/cm² damage threshold
- Long-term interferometric stability in non-temperature-controlled environments
