621 research outputs found
X-ray absorption via electron-ion bremsstrahlung in Maxwellian plasma at the exact consideration of Coulomb potential
Based on the results of exact consideration of electron-ion Coulomb
interaction, by numerical simulations for ultimate absorption coefficient, we
study the practically more interesting case of absorption of hard x-ray quanta
of frequency when photon energy is of the order of plasma temperature, in high
temperature plasma, within the high nuclear charges as well (at which the Born
approximation is not applicable), constituting the temperature dependence of
one-photon absorption coefficient. It is shown that one can achieve the
efficient absorption coefficient in these cases.Comment: 5 pages, 4 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
Nonlinear absorption of high-intensity shortwave radiation in plasma within relativistic quantum theory
On the base of the quantum kinetic equation for density matrix in plasma at
the stimulated bremsstrahlung of electrons on ions, the nonlinear absorption
rate for high-intensity shortwave radiation in plasma has been obtained within
relativistic quantum theory. Both classical Maxwellian and degenerate quantum
plasma are considered for x-ray lasers of high intensities. Essentially
different dependences of nonlinear absorption rate on polarization of strong
laser radiation is stated.Comment: 8 pages, 9 figure
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
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
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
Microscopic nonlinear quantum theory of absorption of coherent electromagnetic radiation in doped bilayer graphene
The microscopic quantum theory of nonlinear stimulated scattering of chiral
particles in doped stacked bilayer graphene on Coulomb field of charged
impurities in the presence of strong coherent electromagnetic radiation is
presented. The Liouville-von Neumann equation for the density matrix is solved
analytically. Here the interaction of electrons with the scattering potential
is taken into account as a perturbation. The absorption rate of nonlinear
inverse-bremsstrahlung for a grand canonical ensemble of fermionic chiral
particles is calculated using the obtained solution. The analysis of the
obtained rate shows that in the terahertz and near-infrared range of
frequencies there is significant absorption of incident radiation via
multiphoton stimulated bremsstrahlung mechanism.Comment: 13 pages, 6 figures. arXiv admin note: substantial text overlap with
arXiv:1907.04692 and arXiv:1710.0368
Multiphoton cross sections of conductive electrons stimulated bremsstrahlung in doped bilayer graphene
The quantum theory of multiphoton stimulated bremsstrahlung of charged
carriers on an arbitrary electrostatic potential of impurity ion in doped
bilayer graphene at the presence of coherent electromagnetic radiation is
developed. A terahertz wave field is considered exactly, while the
electrostatic potential of doped ions as a perturbation. The essentially
nonlinear response of bilayer graphene to a pump wave and significant
differences from the case of a single layer graphene are shown, which can be
associated to nonlinear parabolic dispersion. The latter opens new way to
manipulate with the electronic transport properties of conductive electrons of
bilayer graphene by coherent radiation field of terahertz or near-infrared
frequencies.Comment: 15 pages, 7 figures. arXiv admin note: text overlap with
arXiv:1703.06854, arXiv:1710.0368
The Dependence of the Age Parameter from EAS Size and Zenith Angle of Incidence
The quality of the MAKET-ANI detector installation in view of the uniformity
of the registration efficiency is demonstrated. Based on a data sample
collected by the MAKET-ANI array in the period of June 1997 - March 1999, the
dependencies of the age parameter on the zenith angle and the EAS size
(10^5-10^7) are studied. The variation of the age parameter with the shower
size can be approximately related to the elongation rate.Comment: 6 pages, to appear in the ANI99 workshop proceedings, FZKA report
Forschungszentrum Karlsruhe, ed. by A.Chilingarian, A.Haungs, H.Rebel and
Kh.N.Sanosya
Determination of the EAS Attenuation Length from Data of the ANI Experiment
Using the EAS size spectra measured with the MAKET ANI array on Mt. Aragats,
Armenia (3200m a.s.l.) in the range of the shower size 10^5 - 10^7 for
different angles-of-incidence, the EAS attenuation length has been determined
applying different analysis methods. The analysis is based on a data sample of
2.5*10^6 events collected in the period of June, 97 - April, 99. The results
are compared with results deduced from data of the EAS TOP and KASCADE
experiments.Comment: 9 pages, to appear in the ANI99 workshop proceedings, FZKA report
Forschungszentrum Karlsruhe, ed. by A.Chilingarian, A.Haungs, H.Rebel and
Kh.N.Sanosya
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