Hot/Cold Mirrors
Cold mirrors reflect some or all of the visible range and transmit the IR. Cold mirrors are used in applications where it is desirable to reflect a cool beam of visible light and remove the heat by transmission. Cold mirrors are typically used at 45 degrees angle to the light source. Cold mirrors effectively reflect the visible light to the object while allowing heat to pass through.
Hot mirrors, which reflect heat energy, are quite effective in space-limited applications. Because the hot mirror is a short wavepass filter, attempts to extend the width of the reflecting band beyond about 1.2 µm usually result in a loss of visible transmission caused by high order interference effects. Although the heat rejection characteristics of a hot mirror are less than those of a cold mirror, hot mirrors may prove to be equally effective when they are matched properly to the spectral response of the energy source and the optical system.
