The 10Z20DM.4 Laser Line Dielectric mirror is a highly efficient reflector optimized for the 632.8 nm wavelength. This 1 inch (25.4 mm) diameter mirror is made from a 6.0 mm thick Zerodur substrate. Zerodur is a glass-ceramic material where thermal expansion is nominally zero. This extra stability can be critical for applications requiring diffraction limited performance. The DM.4 coating is designed for use with HeNe lasers and has a center wavelength of 632.8 nm. The coating achieves greater than 99% reflectance, from 0–45° angle of incidence, for any polarization. This multilayer dielectric coating is extremely durable, making it resistant to damage from repeated cleaning. This mirror has a λ/10 surface flatness and a 15-5 surface quality.