The 10Z20ER.4 Broadband Metallic Mirror is an excellent general purpose, broadband reflectors. 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 ER.4 protected gold coating is ideal for applications requiring broadband reflectance in the near IR to the far IR. A multilayer dielectric overcoat provides protection to the gold from the environment. Average reflectivity is greater than 96% from 650–1700 nm and greater than 98% from 1.7–20 μm. This mirror has a λ/10 surface flatness and a 15-5 surface quality.