Mirrors are 'devices' that reflect photons. The first mirrors were slabs of reflective glass of vulcanic origin, later polished metal was used. Modern mirrors are either metalized mirrors or dielectric mirrors.

Metalized mirrors consists of one or more layers of metal on a glass substate. Normaly the glass is given a thin layer of nickel, chromium or titanium. On this layer, a thicker layer of aluminium or silver is applied. On normal mirrors the glass side is used to reflect the light, so the backside gets a dark protective coating to protect the metal from water. Mirrors used in for example scanners need a lower distortion, so the metal side is used as reflector, and gets a transparent silicon layer instead. When light hits the metal, the metal atom's electrons are excited. This creates an electric field that deflects the photons(since photons are charged particles) of the light. But the process absorbs some of the light energy, so this type of mirror is only about 95% effective.

Dielectric mirrors have a nonconductive reflective material. A pane of glass or a pool of water is a dielectric reflector, though not very effective. To make a mirror several layers of a plastic or glass dielectric are used. Each layer only reflects a small amount of light. The thickness of the layers is carefully chosen so the reflected lightwaves enforce each other. These mirrors can have over 99% reflectivity, but are usually only reflective at a limited angle. But in the last five years a dielectric mirror type is developed that has a much broader angle(especialy in the IR range). It consists of alternating layers of polystyrene and tellurium.