Sparseness of Natural Oscillations Spectrum for Double-Mirror Open Resonator Using Mode-Selective Scatterers on One of Mirrors Surface

The effective procedure for spectrum sparseness of natural oscillations of double-mirror open resonators (OR) is proposed. It is based on the placement of scatterers with a specially determined geometric profile on one of the mirrors surface, forming the single mode-selective reflector. This procedure is used to synthesize two profiles of these scatterers for OR with flat and cylindrical mirrors. We propose the rectangular metal bar and the echelette-corner reflector with three rectangular steps symmetric to the plane of resonator symmetry. These scatterers placed on the flat OR mirror provide a minimal effect on the spatial-frequency characteristics of the operating natural oscillation, and significantly reduce the Q-factor of most of the rest oscillations. The spectral characteristics of the OR with these inserts are calculated for excitation by the current source and the eigen mode of a supply waveguide. The possibility of significant decrease in the number of OR natural oscillations is shown, in comparison with the resonator without these scatterers. The effect of increasing the radiation Q-factor of operating oscillation is observed using the echelette-corner scatterer. The technique used to determine the scatterers geometric profile is suitable for spectrum sparseness of the OR of arbitrary dimensions with mirrors of any shapes.