Development of Optical Windows for High Temperature Applications

Frictional heating of optical windows and domes can be mitigated using spectrally selective high emissivity thin films and optical interference filters. The three mechanisms of heat transport in materials are conduction, convection and radiative emission. Conduction and convection are linearly dependent on the difference in local temperature  between materials in contact. Radiative emission is a function of the absolute temperature of the material to the fourth power and can be the dominate mechanism of heat transfer in air or vacuum environments for materials at elevated temperature. This program will develop high temperature optical coatings with selective emissivity’s to mitigate window and dome temperatures as well as block the transmission of out of band thermal radiation from reaching internal optics and components.