Smooth variations of spectral characteristics as functions of nonspectral parameters may be violated in the regions where interaction of oscillations (and waves) of gratings corresponding to different eigenvalues (fundamental frequencies k or longitudinal wavenumbers Φ) is observed. This phenomenon takes place when spectral points approach each other in the complex space and the conditions providing existence of eigenoscillations or eigenwaves belonging to one symmetry class but different families become close and they exchange their spectral characteristics.

Inspec keywords: eigenvalues and eigenfunctions; diffraction gratings

Other keywords: eigenoscillations; intertype oscillations; spectral theory; open structures excitation; Morse critical points; eigenvalues; oscillations interaction; eigenwaves; gratings waves; nonspectral parameters

Subjects: Gratings, echelles