Selection of the higher transverse modes of a waveguide quasi-optical resonator

A method of spatial filtration for the selective excitation of individual higher-order transverse oscillation modes with a high degree of discrimination of undesirable modes in a waveguide quasi-optical resonator is described. The method is based on the use of a mirror with absorbing or scattering inhomogeneities discretely arranged on its surface. The efficient excitation of such modes in a waveguide dielectric resonator with a nonuniform amplitude-step mirror in the submillimetre wavelength range (at 0.4326 mm) is confirmed theoretically and experimentally.