The 05D20DM.4 Laser Line Dielectric mirror is a highly efficient reflector optimized for the 632.8 nm wavelength. This 1/2 inch (12.7 mm) diameter mirror is made from a 3.1 mm thick Borofloat® 33 substrate. Borofloat has low thermal expansion and is an excellent substrate for most applications. 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.