Questions about Reflection Gratings

10.6 microns

  • Soda Lime glass (float): 9×10-6/degreeC
  • Annealed Borosilicate (Pyrex): 3×10-6/degreeC
  • Zerodur: 0.1×10-6/degreeC

The limit is ±0.5% but most gratings are typically much better.

  • AlmgF2 – protects aluminum from oxidation, maintaining original high reflectance of aluminum in VIS & UV
  • AU-3 – Increases reflectivity but may reduce damage threshold by a factor of 2 or more
  • AR (Anti-Reflective) – Cuts down on reflectance
  • AlmgF3 – Overcoat for improved UV reflectance

Dispersion required and efficiency at peak wavelength are often trade-offs. Coarse gratings, for example, generally have higher peak efficiency but lower dispersion.

For reflection gratings there is none and it’s more expensive. Fused silica’s advantage over Zerodur applies only to transmissive optics due to its ability to pass UV light.