High laser harmonics induced by the Berry curvature in time-reversal invariant materials

A new nonlinear scheme of high harmonics generation in a wide class of time-reversal invariant materials with broken spatial inversion symmetry (where recently the nonlinear Hall effect has been established) due to the nontrivial topology of bands is proposed. A microscopic quasiclassical theory describing the nonperturbative optical response of pseudo-relativistic electrons with nonzero Berry curvature of bands to a strong laser field is developed. We analyze the harmonic content of the induced current and show that one can decouple induced laser harmonics solely by the Berry curvature of bands. We also study the dependence of the nonlinear response on the driving wave and system parameters.Comment: 8 pages, 5 figure

Two-level system with broken inversion symmetry coupled to a quantum harmonic oscillator

We study the generalized Jaynes-Cummings model of quantum optics at the inversion-symmetry-breaking and in the ultrastrong coupling regime. With the help of a generalized multiphoton rotating-wave approximation, we study the stationary solutions of the Schr\"{o}dinger equation. It is shown that the problem is reduced to resonant interaction of two position-displaced harmonic oscillators. Explicit expressions for the eigenstates and eigenvalues of generalized Jaynes-Cummings Hamiltonian are presented. We exemplify our physical model with analytical and numerical considerations regarding collapse and revivals of the initial population of a two-level system and photon distribution function at the direct multiphoton resonant coupling.Comment: 5 pages, 5 figure

Relativistic Quantum Theory of Cyclotron Resonance in a Medium

In this paper the relativistic quantum theory of cyclotron resonance in an arbitrary medium is presented. The quantum equation of motion for charged particle in the field of plane electromagnetic wave and uniform magnetic field in a medium is solved in the eikonal approximation. The probabilities of induced multiphoton transitions between Landau levels in strong laser field is calculated.Comment: 4 pages, RevTe

Relativistic theory of the above-threshold multiphoton ionization of hydrogen-like atoms in the ultrastrong laser fields

The relativistic theory of above-threshold ionization (ATI) of hydrogen-like atoms in ultrastrong radiation fields, taking into account the photoelectron induced rescattering in the continuum spectrum is developed. It is shown that the contribution of the latter in the multiphoton ionization probability even in the Born approximation by Coulomb field is of the order of ATI probability in the scope of Keldysh-Faisal-Reiss ansatz.Comment: REVTeX, 13 page

Quantum Theory of Generation of Coherent X-Ray in a Wiggler

In this paper we present the nonlinear quantum theory of X-Ray FEL in a wiggler. We present the solution of the Dirac equation in a space periodic strong magnetic field, which describes the quantum dynamics of a single electron in a wiggler. With the help of obtained wave function of an electron the self-consistent set of the Maxwell and relativistic quantum kinetic equations is obtained. Then, the process of coherent X-ray radiation generation in nonlinear quantum regime, when the photon energy is larger than resonance widths due to energetic/angular spreads of an electron beam and resonance width caused by finite interaction length, is investigated.Comment: 11 pages, RevTe

On the theory of the relativistic cross sections for stimulated bremsstrahlung on an arbitrary electrostatic potential in the strong electromagnetic field

On the base of relativistic generalized eikonal approximation wave function the multiphoton cross sections of a Dirac particle bremsstrahlung on an arbitrary electrostatic potential and strong laser radiation field are presented. In the limit of the Born approximation the ultimate analytical formulas for arbitrary polarization of electromagnetic wave have been obtained.Comment: Revtex,10 pages,3 figure

Relativistic quantum theory of high harmonic generation on atoms/ions by strong laser fields

High-order harmonic generation (HHG) by hydrogenlike atoms/ions in the uniform periodic electric field, formed by the two linearly polarized counterpropagating laser beams of relativistic intensities, is studied. The relativistic quantum theory of HHG in such fields, at which the impeding factor of relativistic magnetic drift of a strong wave can be eliminated, is presented arising from the Dirac equation. Specifically, a scheme of HHG in underdense plasma with the copropagating ultraintense laser and fast ion beams is proposed.Comment: 8 pages, 8 figures, Conference: Photons, Atoms, and Qubits 2007 (PAQ07, paper 47

Harmonics generation and intense terahertz radiation from polar molecules at multiphoton resonant excitation in laser fields

The coherent radiation spectrum of two-level polar molecules with UV transition is studied at the multiphoton resonant excitation by a moderately strong laser field. The spectrum corresponding to harmonic generation and low-frequency radiation is investigated both analytically and numerically. Specifically, a mechanism for generation of intense smoothly tunable terahertz radiation by two-level molecular configurations (with dynamic Stark shifts) possessing permanent dipole moments, is considered.Comment: 8 pages, 6 figure

Multiphoton Resonant Transitions of Electrons in the Laser Field in a Medium

Within the scope of the relativistic quantum theory for electron-laser interaction in a medium and using the resonant approximation for the two degenerated states of an electron in a monochromatic radiation field [1] a nonperturbative solution of the Dirac equation (nonlinear over field solution of the Hill type equation) are obtained. The multiphoton cross sections of electrons coherent scattering on the plane monochromatic wave at the Cherenkov resonance are obtained taking into account the specificity of induced Cherenkov process [1, 2] and spin-laser interaction as well. In the result of this resonant scattering the electron beam quantum modulation at high frequencies occurs that corresponds to a quantity of an electron energy exchange at the coherent reflection from the ''phase lattice'' of slowed plane wave in a medium. So, we can expect to have a coherent X-ray source in induced Cherenkov process, since such beam is a potential source of coherent radiation itself.Comment: 6 pages, REVTE

Enhanced harmonic generation and wave-mixing via two-color multiphoton excitation of atoms/molecules

We consider harmonics generation and wave-mixing by two-color multi photon resonant excitation of three-level atoms/molecules in strong laser fields. The coherent part of the spectra corresponding to multicolor harmonics generation is investigated. The obtained analytical results on the basis of generalized rotating wave approximation are in a good agreement with numerical calculations. The results applied to the hydrogen atom and homonuclear diatomic molecular ion show that one can achieve efficient generation of moderately high multicolor harmonics via multiphoton resonant excitation by appropriate laser pulses.Comment: 7 pages, 6 figure