O. V. Tikhonova

Strong-field atomic stabilization: numerical simulation and analytical modelling

The phenomenon of strong laser field atomic stabilization is discussed. Earlier suggested models and mechanisms of stabilization are described: A- 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 Schrodinger 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.

Bright squeezed-vacuum source with 1.1 spatial mode

Bright squeezed vacuum, a macroscopic nonclassical state of light, can be obtained at the output of a strongly pumped nonseeded traveling-wave optical parametric amplifier (OPA). By constructing the OPA of two consecutive crystals separated by a large distance, we make the squeezed vacuum spatially single-mode without a significant decrease in the brightness or squeezing.

Nonlinear polarization response of an atomic gas medium in the field of a high-intensity femtosecond laser pulse

Polarization response that appears in silver vapors in the field of a high-intensity femtosecond Ti:sapphire laser has been studied by the direct numerical integration of the time-dependent Schrödinger equation. The regions of applicability have been determined for perturbation theory and the power series expansion of the polarization in the field. The contribution of free electrons to the response at the frequency of the interacting field has been calculated, which is due to the photoionization process and limits the Kerr effect. An important contribution of laser-excited atomic states to nonlinear atomic responses of neutral atoms has been demonstrated.

Schmidt modes in the angular spectrum of bright squeezed vacuum

We investigate both theoretically and experimentally strong correlations in macroscopic (bright) quantum states of light generated via unseeded parametric down-conversion and four-wave mixing. The states generated this way contain only quantum noise, without a classical component, and are referred to as bright squeezed vacuum (BSV). Their important advantage is the multimode structure, which offers a larger capacity for the encoding of quantum information. For the theoretical description of these states and their correlation features we introduce a generalized fully analytical approach, based on the concept of independent collective (Schmidt) modes and valid for the cases of both weak and strong nonlinear interaction. In experiment, we generate states of macroscopic BSV with up to

Applicability of the Kramers-Henneberger approximation in the theory of strong-field ionization

{10}^{10}

Tunneling ionization of a hydrogen atom in short and ultrashort laser pulses

photons per mode and examine large photon-number spatial correlations that are found to be very well described by our theoretical approach.

Numerical investigation of atomic dynamics in strong ultrashort laser pulses

The ionization of the one-dimensional model system with a short-range potential by a linearly polarized laser field is studied by direct numerical integration of the non-stationary Schrodinger equation. The results are interpreted in terms of both field-free atomic states and Kramers-Henneberger (KH) eigenstates. The dynamics of the system is analysed to determine which potential (atomic or KH) is physically more appropriate to describe the ionization process. The justification of the KH approach is also examined. A new limitation of the validity of the KH approximation is found to exist in the case of low laser frequencies.

Different regimes of strong-field dynamics of atoms in intense low-frequency laser pulses

The ionization of a hydrogen atom in a linearly polarized low-frequency electromagnetic field is investigated by direct numerical integration of the time-dependent Schrödinger equation. The data obtained for various ionization regimes and various initial atomic states are compared with the Keldysh and Perelomov-Popov-Terent’ev (PPT) theories. The validity ranges for the quasi-static model of tunneling ionization and the PPT theory in laser intensity and frequency are determined. The tunneling ionization of the excited 2s and 2p states is discussed. The ionization of a hydrogen atom in an ultrashort (on the order of one optical period) pulse is investigated.

Atom under an intense laser pulse: Stabilization effect and strong-field approximation

The algorithms for the numerical solution of the stationary and nonstationary Schrödinger equations that allow the analysis of the dynamics of single-electron atoms in the presence of an external strong linearly polarized electromagnetic field in the dipole approximation are presented. Several examples of the simulation of atomic dynamics in the presence of high-intensity laser fields are considered to illustrate the possibilities of the proposed algorithms.

Ionization and stabilization of atoms in a high-intensity, low-frequency laser field

In this work, the dynamics of a 3D hydrogen atom in an intense ultrashort low-frequency laser pulse is investigated by direct numerical integration of the non-stationary Schrödinger equation in a wide range of laser pulse parameters. Significantly different regimes of ionization are found to exist. In the case when the Keldysh parameter is much less than unity, but the laser intensity exceeds the barrier suppression threshold, the atomic behavior is found not to correspond to the tunneling ionization and is shown to reveal the features of the Kramers--Henneberger regime, resulting in the stabilization phenomenon. The applicability range of the re-scattering scenario is discussed.