Spectroscopy of the atomic system driven by high intensity laser field

Spontaneous emission of the quantum system driven by a high intensity classical laser field is analyzed. The study is based on the accurate consideration of quantum system interaction with vacuum quantized field modes in the first order of perturbation theory, while the intense laser field is considered classically beyond the perturbation theory. It is demonstrated that the spectrum of the spontaneous emission can be used for analyzing of the strong-field dynamics and structure of the energy spectrum of the atomic system. The obtained data are compared with that obtained in the frames of semiclassical approximation typically used for analyzing of the strong-field dynamics. It is found that the applicability of the semiclassical approach is strictly limited.