Quasi-hemispherical fabry-perot resonator and method of operating the same

A quasi-hemispherical Fabry-Perot resonator for the non-destructive and contact-free as well as temperature-dependent and localized determination of the surface resistance Rs of electrically conductive thin material films, comprising disposed in a vacuum chamber:

• a spherical mirror having a center axis and delimiting a resonator space, said mirror having a high surface quality and two coupling openings for the incoupling and the out-coupling of a millimeter wave into, and out of, said resonator space, said in- and out-coupling openings being disposed adjacent each other and in close proximity to said center axis, a planar mirror arranged in spaced relationship from said spherical mirror so as to be centered on said center axis opposite said spherical mirror and delimiting the resonator space opposite said spherical mirror, said planar mirror having a high electrical conductivity and being adapted to support a wafer provided with a thin film material to be examined, a cryostat cooling arrangement connected to said mirrors for monitoring the mirrors for a predetermined temperature, said cooling arrangement including an inner and an outer radiation shield disposed within one another and enclosing said planar and spherical mirrors, said radiation shields being disposed in heat transfer uncoupled relationship and each including a base plate with cooling passages through which coolant is conducted and having metallic walls with mirrored surfaces;
• the inner radiation shield enclosing said spherical and planar mirrors with the resonator space therebetween, said spherical mirror being supported on the base plate of said inner radiation shield in good heat transfer relation therewith, a support plate supporting said radiation shields, an extension arm supported at one end by said support plate and having an opposite end extending through said radiation shields into the interior thereof and carrying therein said planar mirror, the opposite end of said support arm being movable in the direction of said center axis and sidewardly, and also being rotatable and consisting of a material having a low heat conductivity, said planar mirror being mounted on said opposite end of said extension arm, said opposite end being disposed in heat transfer relation with said base plate by a flexible band of high heat conductivity and sufficient length to permit rotation of the planar mirror about the resonator axis by up to 360°, a first support arm mounted pivotally at one end centrally on said inner base plate and supporting at its other end a section of said inner radiation shield disposed opposite said spherical mirror and behind said planar mirror, a second support arm mounted pivotally at one end centrally on said outer base plate and supporting at its other end a section of said outer radiation shield disposed adjacent said inner radiation shield section, said end of said extension arm extending through said radiation shield sections and being engaged thereby such that said inner and outer radiation shield sections are carried along with said arm extension upon side movement thereof so that said inner and outer radiation shields remain closed to prevent radiation leaks, and both mirrors of said resonator having a heat capacity sufficient to render a thermal distortion of the resonator during a reading period for a resonance negligible.