| Material | Aluminium |
| Diameter tolerance | +0/-0.4 mm |
| Clear aperture | >80 % |
| Focal length tolerance | ±1 % |
| Surface roughness | <17.5 nm (RMS) |
| Surface figure | <λ/4 @ 632.8 nm (RMS) |
| Laser damage threshold |
Protected Aluminum: >0.25 J/cm² for 10 ns pulses @1064 nm Protected Gold: >0.9 J/cm² for 10 ns pulses @1064 nm |
The main property of Off-axis parabolic mirror is to focus light at an angle with beam propagation axis. This allows to avoid comatic aberration (or coma) that would emerge in case of using spherical mirror at an angle. Off-axis parabolic mirrors come into assistance where usage of transmitting optics is limited, for example due to chromatic aberrations, group velocity dispersion (GVD) or spectral bandwidth. Standard items comprise parabolic mirrors machined by diamond turning technique and coated with protected gold and silver coatings.