The phenomenon of strong laser field atomic stabilization is discussed. Earlier suggested models and mechanisms of stabilization are described: Λ- and V-type interference stabilization of Rydberg atoms, adiabatic (Kramers–Henneberger) and high-frequency stabilization of neutral atoms and negative ions, and so on. Both numerical and analytical approaches to the description of these phenomena are discussed. In this context, ab initio numerical solutions of the nonstationary Schrödinger equation, obtained by several groups of authors, are overviewed. Based on the most modern and recent solutions of this type, mechanisms of stabilization of a hydrogen atom are shown to vary with varying intensity and frequency of a laser field. Such an evolution and applicability condition of various stabilization mechanisms is described. Limitations arising due to relativistic effects are discussed. Existing experiments on strong-field stabilization are overviewed and their interpretation is considered.

Frolov, M. V.; Manakov, N. L.; Popov, A. M.; Tikhonova, O. V.; Volkova, E. A.; Silaev, A. A.; Vvedenskii, N. V.; and Starace, Anthony F., "Analytic theory of high-order-harmonic generation by an intense few-cycle laser pulse" (2012 We present a theoretical model for describing the interaction of an electron, weakly bound in a short-range potential, with an intense, few-cycle laser pulse. General definitions for the differential probability of abovethreshold ionization and for the yield of high-order-harmonic generation (HHG) are presented. For HHG we then derive detailed analytic expressions for the spectral density of generated radiation in terms of the key laser parameters, including the number N of optical cycles in the pulse and the carrier-envelope phase (CEP). In particular, in the tunneling approximation, we provide detailed derivations of the closed-form formulas presented briefly by M. V. Frolov et al. [Phys. Rev. A 83, 021405(R) (2011)], which were used to describe key features of HHG by both H and Xe atom targets in an intense, few-cycle laser pulse. We then provide a complete analysis of the dependence of the HHG spectrum on both N and the CEP φ of an N -cycle laser pulse. Most importantly, we show analytically that the structure of the HHG spectrum stems from interference between electron wave packets originating from electron ionization from neighboring half-cycles near the peak of the intensity envelope of the few-cycle laser pulse. Such interference is shown to be very sensitive to the CEP. The usual HHG spectrum for a monochromatic driving laser field (comprising harmonic peaks at odd multiples of the carrier frequency and spaced by twice the carrier frequency) is shown analytically to occur only in the limit of very large N , and begins to form, as N increases, in the energy region beyond the HHG plateau cutoff.

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PACS 42.50.Ct -Quantum description of interaction of light and matter; related experiments PACS 32.80.Fb -Photoionization of atoms and ions PACS 32.80.Ee -Rydberg states Abstract -A new approach to the study of the spontaneous emission of the quantum system driven by a high-intensity laser field is developed. This approach 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 which allows to observe any-order stimulated processes governed by classical field. The proposed approach is applied to the study of a number of quantum systems in intense laser field. The obtained data are compared with those obtained in the frames of semiclassical approximation typically used for analyzing of the strong-field dynamic. It is found that the applicability of the semiclassical approach is strictly limited. It is valid for calculation of transitions to the initially populated state only if the population of this state is close to unity during the pulse and in the after-pulse regime. If its population is depleted, the semiclassical approach fails.