L P Rapoport

Bio: L P Rapoport is an academic researcher from Voronezh State University. The author has contributed to research in topics: Field (physics) & Scattering. The author has an hindex of 5, co-authored 6 publications receiving 295 citations.

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

Abstract: 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.

The use of a model potential for the calculation of atomic multiphoton ionisation probabilities

Abstract: A method is developed for calculating the multiphoton ionisation probabilities of atoms based on the use of the Green's function of the optical electron, obtained with the help of the model-potential method. The compound matrix elements of perturbation theory are presented in the form of rapidly convergent hypergeometric-type series, which are easily computed. The multiphoton ionisation probabilities of alkali metals, rare gases and mercury atoms are calculated in a wide range of frequencies. The results indicate sufficient accuracy and convenience of the method developed.

Tunnel and multiphoton ionization of atoms and ions in a strong laser field (Keldysh theory)

Abstract: The theoretical description of the nonlinear photoionization of atoms and ions exposed to high-intensity laser radiation is underlain by the Keldysh theory proposed in 1964. The paper reviews this theory and its further development. The discussion is concerned with the energy and angular photoelectron distributions for the cases of linearly, circularly, and elliptically polarized laser radiation, with the ionization rate of atomic states exposed to a monochromatic electromagnetic wave and to ultrashort laser pulses of various shape, and with momentum and angular photoelectron spectra in these cases. The limiting cases of tunnel (γ 1) and multiphoton (γ 1) ionization are discussed, where c is the adiabaticity parameter, or the Keldysh parameter. The probability of above-barrier ionization is calculated for hydrogen atoms in a low-frequency laser field. The effect of a strong magnetic field on the ionization probability is discussed. The process of Lorentz ionization occurring in the motion of atoms and ions in a constant magnetic field is considered. The properties of an exactly solvable model—the ionization of an s-level bound by zero-range forces in the field of a circularly polarized electromagnetic wave—are described. In connection with this example, the Zel'dovich regularization method in the theory of quasistationary states is discussed. Results of the Keldysh theory are compared with experiment. A brief discussion is made of the relativistic ionization theory applicable when the binding energy of the atomic level is comparable with the electron rest mass (multiply charged ions) and the sub-barrier electron motion can no longer be considered to be nonrelativistic. A similar process of electron-positron pair production from a vacuum by the field of high-power optical or X-ray lasers (the Schwinger effect) is considered. The calculations invoke the method of imaginary time, which provides a convenient and physically clear way of calculating the probability of particle tunneling through time-varying barriers. Discussed in the Appendices are the properties of the asymptotic coefficients of the atomic wave function, the expansions for the Keldysh function, and the so-called 'ADK theory'.

Keldysh theory of strong field ionization: history, applications, difficulties and perspectives

Abstract: The history and current status of the Keldysh theory of strong field ionization are reviewed. The focus is on the fundamentals of the theory, its most important applications and those aspects which still raise difficulties and remain under discussion. The Keldysh theory is compared with other nonperturbative analytic methods of strong field atomic physics and its important generalizations are discussed. Among the difficulties, the gauge invariance problem, the tunneling time concept, the conditions of applicability and the application of the theory to ionization of systems more complex than atoms, including molecules and dielectrics, are considered. Possible prospects for the future development of the theory are also discussed.