Material aspects of high power microwave windows

Summary form only given. The candidate materials for high power mm-wave window materials like sapphire, boron nitride, high-resistivity silicon, CVD-diamond and silicon carbide will be presented and the production technology briefly described. The material parameters will be discussed which are most relevant for high power operation. Experimental data of absorption values in selected grades of window materials will be reported resulting from measurements at frequencies from 40 GHz up to 380 GHz and in the temperature interval of 40-900 K. The main absorption mechanisms for ultra-low loss materials will be described and prospects will be given for advancing these materials in the THz region. It will be shown that CVD diamond is the only material currently available with a transmission capability of several Megawatt in CW operation and that CVD Diamond is the primary candidate material for high-power THz applications.