Dielectric materials for gyrotron output windows

The dielectric parameters of materials for gyrotron output windows measured in the range 65–300 GHz are given. The special attention is paid to the spread of values of the refractive index and loss tangent of dielectrics produced by different firms. The refractive index and loss tangent are measured for sapphire at the cryogenic temperatures and for boron nitride and silica glass at the temperatures 300–1000K.