High-order harmonic generation in gapped bilayer graphene

Microscopic nonlinear quantum theory of interaction of coherent electromagnetic radiation with gapped bilayer graphene is developed. The Liouville-von Neumann equation for the density matrix is solved numerically at the multiphoton excitation regime. The developed theory of interaction of charged carriers with strong driving wave field is valid near the Dirac points of the Brillouin zone. We consider the harmonic generation process in the nonadiabatic regime of interaction when the Keldysh parameter is of the order of unity. On the basis of numerical solutions, we examine the rates of odd and even high-harmonics at the particle-hole annihilation in the field of a strong pump wave of arbitrary polarization. Obtained results show that the gapped bilayer graphene can serve as an effective medium for generation of even and odd high harmonics in the THz and far infrared domains of frequencies.Comment: 15 pages, 9 figure

Collective two-boson decay of excitons in Bose-Einstein condensate and generation of coherent photon-phonon radiation

The collective decay of excitons from initial Bose-Einstein condensate state is investigated theoretically. As practically more interesting case we consider excitons of the yellow series in the semiconductor cuprous oxide where we have collective photon and phonon assisted decay of excitons. It is shown that because of intrinsic instability of recoilless two-boson decay of Bose-Einstein condensate, the spontaneously emitted bosonic pairs are amplified leading to an exponential buildup of a macroscopic population into the certain modes. The collective decay rate has a nonlinear dependence on the excitonic density being comparable or larger than Auger recombination loss rate up to the high densities, which makes obtainable its observation. The considering phenomenon can also be applied for the realization of phonon laser.Comment: 12 pages, 1 figur

Multiphoton interaction of a qutrit with single-mode quantized field in the ultrastrong and deep strong coupling regimes

We consider multiphoton dynamics of a quantum system composed of a three-state atom (a qutrit) and a single-mode photonic field in the ultrastrong and deep strong coupling regimes, when the coupling strength is comparable to or larger than the oscillator energy scale. We assume a qutrit to be in a polar-$\Lambda$ configuration in which two lower levels have mean dipole moments. Direct multiphoton resonant transitions revealing generalized Rabi oscillations, collapse, and revivals in atomic excitation probabilities for the ultrastrong couplings are studied. In the deep strong coupling regime particular emphasis is placed on the ground state of considering system which exhibits strictly nonclassical properties.Comment: 10 pages, 12 figures, Submitted to Phys. Rev.

Multiphoton excitation and high-harmonics generation in topological insulator

Multiphoton interaction of coherent electromagnetic radiation with 2D metallic carriers confined on the surface of the 3D topological insulator is considered. A microscopic theory describing the nonlinear interaction of a strong wave and metallic carriers with many-body Coulomb interaction is developed. The set of integrodifferential equations for the interband polarization and carrier occupation distribution is solved numerically. Multiphoton excitation of Fermi-Dirac sea of 2D massless carriers is considered for a THz pump wave. It is shown that in the moderately strong pump wave field along with multiphoton interband/intraband transitions the intense radiation of high harmonics takes place.Comment: 13 pages, 7 figure

Third harmonic generation in gapped bilayer graphene

With the help of numerical simulations in microscopic nonlinear quantum theory of coherent electromagnetic radiation interaction with a gapped bilayer graphene, we find out the optimal values of pump wave intensity, graphene temperature, and energy gap induced by a constant electric field for practically significant third order harmonic coherent emission. The Liouville-von Neumann equation is treated numerically for the third harmonic generation in multiphoton excitation regime near the Dirac points of the Brillouin zone. We examine the rates of the third harmonic at the particle-hole annihilation in the field of a strong pump wave of linear polarization for practically real/optimal parameters of a considering system. The obtained results show that by choosing the optimal values of the main characteristic parameters, a gapped bilayer graphene can serve as an effective medium for generation of the third harmonic at room temperatures in the terahertz and far infrared domains.Comment: 7 figure

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

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

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

Microscopic quantum theory of nonlinear absorption of strong electromagnetic radiation in doped graphene

Microscopic quantum theory of nonlinear stimulated scattering of 2D Dirac particles in doped graphene on Coulomb field of impurity ions at the presence of an external strong coherent electromagnetic radiation is developed. We consider high Fermi energies and low frequencies (actually terahertz radiation) to exclude the valence electrons excitations. The Liouville-von Neumann equation for the density matrix is solved analytically, taking into account the interaction of electrons with the scattering potential in the Born approximation. With the help of this solution, the nonlinear inverse-bremsstrahlung absorption rate for a grand canonical ensemble of 2D Dirac fermions is calculated. It is shown that one can achieve the efficient absorption coefficient by this mechanism.Comment: 11 pages, 4 figures. arXiv admin note: substantial text overlap with arXiv:1703.0685

Induced nonlinear cross sections of conductive electrons scattering on the charged impurities in doped graphene

Relativistic quantum theory of induced scattering of 2D Dirac particles by electrostatic field of impurity ion (in the Born approximation) in the doped graphene at the presence of an external electromagnetic radiation field (actually terahertz radiation, to exclude the valence electrons excitations at high Fermi energies) has been developed. It is shown that the strong coupling of massless quasiparticles in the quantum nanostructures to a strong electromagnetic radiation field leads to the strongly nonlinear response of graphene, which opens diverse ways for manipulating the electronic transport properties of conductive electrons by coherent radiation fields.Comment: 8 pages, 7 figure