Metallic Mirrors

These mirrors provide a high reflectance over a very broad spectral bandwidth. They are manufactured by coating with a reflective metal film and then with a dielectric overcoat. This protects the mirror and enhances the reflectivity. Metal coatings available include aluminium, silver and gold. Each metal has a different spectral characteristic. Aluminium creates a good general purpose visible range mirror. Silver has a very high reflectance over the visible and near infrared range. Gold is the preferred coating for infra-red applications at wavelengths greater than 2 microns. The mirror substrates are highly polished laser grade substrates with λ/10 surfaces and low scatter. Metallic mirrors can be used over a wide range of angles of incidence. However, they do affect the state of polarization of the reflected beam.