Inelastic processes in the interaction of an atom with an ultrashort electromagnetic pulse

Electron transitions occurring during the interaction of a heavy relativistic atom with a spatially inhomogeneous ultrashort electromagnetic pulse are considered by solving the Dirac equation. The corresponding transition probabilities are expressed in terms of known inelastic atomic form factors, which are widely used in the theory of relativistic collisions between charged particles and atoms. By way of example, the inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-like atoms are considered. The probabilities of ionization and production of a bound-free electron-positron pair on a bare nucleus, which are accompanied by the formation of a hydrogen-like atom in the final state and a positron in the continuum, are calculated. The developed technique makes it possible to take into account exactly not only the spatial inhomogeneity of an ultrashort electromagnetic pulse, but also the magnetic interaction.     

Interaction of a Hydrogen-Like Atom with an Ultrashort Pulse of Electromagnetic Waves

In the approximation of sudden perturbations, a solution of the Dirac equation describing the behavior of a hydrogen-like atom interacting with a spatially inhomogeneous ultrashort pulse of electromagnetic waves is derived. As an example, the single-electron inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-like atoms are considered. The method developed here allows the spatial inhomogeneity of the ultrashort pulse of electromagnetic waves to be taken into account.     

Excitation and Emission of an Atom in Its Interaction with an Ultrashort Electromagnetic Field Pulse

Based on the approximation of sudden perturbations, the excitation and ionization of an atom in its interaction with an ultrashort electromagnetic field pulse are examined. The probabilities of excitation and ionization are obtained together with the spectra and cross sections of pulse re-emission by the atom.     

Scattering of an ultrashort electromagnetic radiation pulse by an atom in a broad spectral range

The scattering of an ultrashort electromagnetic pulse by atomic particles is described using a consistent quantum-mechanical approach taking into account excitation of a target and nondipole electromagnetic interaction, which is valid in a broad spectral range. This approach is applied to the scattering of single- and few-cycle pulses by a multielectron atom and a hydrogen atom. Scattering spectra are obtained for ultrashort pulses of different durations. The relative contribution of “elastic” scattering of a single-cycle pulse by a hydrogen atom is studied in the high-frequency limit as a function of the carrier frequency and scattering angle.     

Electron transitions and the spectrum of radiation emitted by an atom interacting with an ultrashort electromagnetic pulse

Electron transitions and the spectrum of radiation emitted by an atom interacting with an ultrashort electromagnetic pulse are studied based on the sudden perturbation approximation. The excitation and ionization probabilities, the spectra of pulse reradiation by the atom, and the reradiation cross sections are calculated. It is concluded that the reradiation of ultrashort electromagnetic pulses by multielectron atoms is of a coherent nature.     

The decay dynamics of a slab of two-level atoms excited by an ultrashort resonant pulse

The decay dynamics of a slab of two-level atoms excited by an ultrashort resonant pulse are analyzed by means of the eigenmodes determined by the interaction of the resonance with the slab geometry. The node structure in the spatio-temporal excited atom distribution and the forward-backward asymmetry are identified with the decays of individual modes and with interference between adjacent modes.     

Electron transitions as a result of interaction between a heavy ion and an ultrashort electromagnetic pulse

The electron transitions arising when a heavy relativistic ion interacts with a spatially nonuniform ultrashort electromagnetic pulse are studied by solving the Dirac equation, and expressions for the excitation and ionization probabilities are derived. One-electron inelastic processes that accompany the interaction between the ultrashort pulses and hydrogen-like atoms are considered by way of example. The approach developed in this article makes it possible to accurately include the spatial nonuniformity of the ultrashort pulse field.     

Diffraction of an ultrashort pulse by a slit

An analysis of a specific feature of the interaction of an ultrashort pulse with a slit is made. Analytical expressions for a monochromatic wave in the form of an ultrashort pulse diffracted by an infinite slit are obtained.     

Spectra induced by interactions of atoms with ultrashort electromagnetic pulses

An ultrashort pulse of an electromagnetic field incident on an atom shakes the atom and gives rise to various electron transitions in it. These processes are accompanied by the reemission of the incident ultrashort pulse. This paper studies the relation between the spectra of reemitted photons of an ultrashort pulse and the transitions of atomic electrons into particular states. The obtained partial reemission spectra can allow one to relate direction patterns to the probability of the excitation of an atom into different states.     

Calculation of the probability of photoprocesses induced by ultrashort electromagnetic pulses

An expression for the total probability of photoprocesses induced by ultrashort electromagnetic pulses in terms of the excited transition cross-section has been derived by using perturbation theory. The expression obtained is valid for any radiation spectral width and for various types of transition: bound-bound and bound-free. By way of illustration the excitation of a two-level system by an ultrashort pulse with a controlled carrier–envelope phase and the photoionization of a hydrogen atom under the action of a sequence of two-cycle electromagnetic pulses are considered.     

Ultrashort optical pulse in an order-disorder ferroelectric in the presence of a lattice of defects

The dynamics of an ultrashort optical pulse in an order-disorder ferroelectric in the presence of a lattice of defects is considered within the microscopic pseudospin formalism in the unidirectional propagation approximation, without limitations on the pulse power. The effective equations for the electric field amplitude and ferroelectric polarization are obtained and numerically solved. Quasi-soliton modes of ultrashort optical pulse propagation in a system with regular defects are revealed and the dependences on the microscopic Hamiltonian parameters are analyzed. The effect of the parameters of defects of different types on the pulse propagation is revealed.     

Formation of Quantum Vortices at the Ionization of an Atom by an Ultrashort Laser Pulse: Two- and Three-Dimensional Cases

Journal of Experimental and Theoretical Physics - Quantum vortices formed at the barrier-suppression ionization of an atom by an ultrashort laser pulse have been studied theoretically and...     

Harmonic Extension and Enhancement Using a Two-Color Chirped Pulse and an Ultrashort Ultraviolet Pulse

A promising method to both extend the harmonic energy and enhance the harmonic intensity is presented when a He atom is exposed to the combination of a two-color chirped pulse and an ultrashort ultraviolet pulse. It is found that: (1) with the introduction of the two chirps, the harmonic energy has been remarkably extended; (2) by properly adding an ultrashort ultraviolet pulse to this synthesized two-color chirped pulse, the harmonic yield is enhanced by 3 orders of magnitude compared with the two-color chirped case; (3) the harmonic spectrum higher than the 96th order shows an ultrabroad supercontinuum with a 395 eV bandwidth, and the proper superposition over the harmonics directly produced a series of intense 40 as pulses which is 3 orders of magnitude higher than that in the two-color chirped case.     

Inelastic processes and interference effects during the interaction of positronium with ultrashort electromagnetic pulses

The excitation, breakup, and reradiation during the interaction of a positronium atom with ultrashort electromagnetic pulses are considered. The probabilities of inelastic processes and reradiation spectra have been obtained. The interference between the amplitudes of the photon emission by the electron and positron is shown to contribute noticeably to the reradiation spectra. The developed approach is applicable for describing the interaction of positronium with ultrashort pulses of attosecond or shorter duration.     

Rabi frequency and optical Bloch equations for a short femtosecond optical pulse

We investigate the interaction of a multilevel atom with a short femtosecond optical pulse beyond the scope of the rotating-wave approximation. We consider the behavior of a three-level atom under the action of two optical pulses resonant with two allowed transitions and a two-level atom under the action of a resonant optical pulse. It is shown that the imaginary part of the off-diagonal elements of the density matrix oscillates with high frequency due to the counter-rotating terms. It is shown also that an effective time-dependent addition to the Rabi frequency exists, which is of importance for ultrashort optical pulses.     

Dissociation of vibrationally excited heteronuclear molecules by an intense infrared field

Results of numerical simulations of the vibrational-rotational dynamics of a molecular system in the field of an intense infrared laser pulse are presented. The cases of quasi-monochromatic and ultrashort laser action on the nuclear subsystem are considered. The influence of the coherent repopulation of vibrationally excited molecular states on photodissociation and the peculiarities of photodissociation under the action of an ultrashort laser pulse are discussed. The results obtained for quasi-monochromatic laser action are interpreted in terms of interference stabilization.     

Interaction of an ultrashort optical pulse with the impurity subsystem of a hydrogen-containing ferroelectric

The dynamics of an ultrashort optical pulse in impurity-containing ferroelectrics with hydrogen bonds has been considered in terms of microscopic pseudospin formalism, which uses the approximation of unidirectional propagation without limitations on the pulse power. The effective equations for the electric field amplitude and ferroelectric polarization have been obtained and numerically solved. Quasi-soliton propagation modes of ultrashort optical pulses are revealed, and their dependences on the microscopic Hamiltonian parameters are analyzed.     

基于FDTD算法研究超短脉冲与二能级原子系统的相互作用

以往对于超短脉冲与二能级原子系统的研究大多基于一些近似方法(慢变包络近似和旋转波近似等),从而求得解析的近似解。但是,由于忽略掉一些有用的光场中的信息,就会造成光场导数项所产生的非线性性质的缺失。本文基于FDTD算法和预测-校正法相结合,建立了预测-校正FDTD算法,用于研究超短脉冲与二能级原子系统的相互作用,以准确地描述光场与原子系统相互作用的特征,验证了面积定理的部分规律;进一步构建了能够实现完全反转原子系统上下能级粒子的短脉冲。相关研究可为目标的特征分析提供参考。     

Ultrahigh Harmonic Generation from an Atom with Superposition of Ground State and Highly Excited States

We investigate the high-order harmonic generation from an atom prepared in a superposition of ground state and highly excited state. When the atom is irradiated by an ultrashort pulse, the cutoff position of the plateau in the harmonic spectrum is largely extended compared with the case that the atom is initially in the ground state. The physics of the extension of the high-order harmonic plateau can be interpreted by the spatial structure of the atomic initial wave packet. We can optimize the generation of high-order harmonics by substituting the excited state for a particular coherent superposition of some highly excited states to form a spatially localized excited wave packet.     

Electron Heating of the Cluster Plasma by an Ultrashort Laser Pulse

JETP Letters - The interaction of an ultrashort (~10 fs) laser pulse with a relativistic intensity (≳1018 W/cm2) with a cluster medium characterized by a random distribution of large,...