Some general properties of quasi-energetic spectra of quantum systems in classical monochromatic fields

Some general features of the quasi-energy dependence on the periodic field frequency and amplitude are examined assuming the discrete character of the quasi-energy spectrum. Jump discontinuities are found in the frequency dependence of the quasi-energy and connected with them band structure of the quasi-energies. A notion of mean energy of a system in a periodic field is introduced and relations between the mean energy and the quasi-energy are investigated. As examples the quasi-energy zones for a two-level system and a rigid rotator are calculated.