Power absorption by surface films on microwave windows

The heating of microwave transmission windows places an effective upper limit on the amount of power that may be transmitted through the window. The mechanical stresses in the window due to thermal gradients can cause window failure even if localized failure initiators such as multipactor (which is of concern only for frequencies below 30 GHz), are ignored. In this paper we investigate the effect of thin surface films on power absorption. Unwanted surface films are known to form on diamond gyrotron windows, while thin films of TiN are intentionally deposited on alumina klystron windows to protect against multipactor.