Search results for "harmonics"
showing 10 items of 199 documents
Corrigendum to “Systematics of azimuthal anisotropy harmonics in proton–nucleus collisions at the LHC from the Color Glass Condensate” [Phys. Lett. B…
2019
Even harmonics generation in plasma as a new tool of current evolution diagnostics
2005
It is shown that using even harmonics of a test wave it is possible to diagnose the fast time evolution of the current density.
High-frequency even harmonics generation in a plasma with electron heat flux
2004
It is shown that in a weakly nonuniform plasma with electron heat flux the generation of odd and even harmonics of high frequency radiation is possible. The even harmonics properties qualitatively differ as compared to those of odd harmonics and depend in an essential way on the heat flux value and orientation with respect to the fundamental wave polarization and propagation directions.
Harmonic Generation and Nonlinear Propagation: When Secondary Radiations Have Primary Consequences
2014
In this Letter, it is experimentally and theoretically shown that weak odd harmonics generated during the propagation of an infrared ultrashort ultraintense pulse unexpectedly modify the nonlinear properties of the medium and lead to a strong modification of the propagation dynamics. This result is in contrast with all current state-of-the-art propagation model predictions, in which secondary radiations, such as third harmonic, are expected to have a negligible action upon the fundamental pulse propagation. By analyzing full three-dimensional ab initio quantum calculations describing the microscopic atomic optical response, we have identified a fundamental mechanism resulting from interfere…
Symmetries in harmonic generation by a two-color field: an application to a simple model atom
1999
We show that the parity of the order of the harmonics generated by a bichromatic field with commensurate frequencies may be related to the invariance properties of the time-dependent Hamiltonian with respect to some suitable transformations. To simplify the mathematical treatment, we have used a simple model atom to perform calculations that show the effects of the relative phase of the driving fields. Harmonic generation has been described as a two-step process that involves replicas of the Stark levels. In agreement with other previous treatments in which other model atoms were used, we have found that a small contamination of the fundamental harmonic can produce significant modifications…
Laser even harmonics generation by a plasma embedded in a static electric field
2004
Even order harmonics generation of the laser radiation due to electron-ion collisions in a plasma embedded in a constant electric field is investigated theoretically. Even harmonics are generated because the presence of a static electric field removes the invariance of the electron distribution function under the symmetry operation of velocity direction inversion. Efficiency generation dependencies are investigatedvsdifferent significant parameters as: harmonics number; the ratio of the electron quiver velocity to the thermal velocity; the orientation of the constant electric field with respect to the laser radiation electric field and its wavevector. It is shown that in the general case th…
Amplification of nonlinear currents generation at harmonics frequencies of submillimeter radiation
2006
The conditions are found when rapid heating of the electrons of a degenerate semiconductor in the presence of two electric fields, one constant and the other variable, is accompanied by the formation of a distribution function significantly departing from the Fermi one. It is also shown that the newly found modification of the electron distribution yields a relative amplification of nonlinear currents generation.
Polarization of high harmonic generated spectra in H+2ion
2013
AbstractWe study the polarization of the harmonics generated by a homonuclear diatomic molecule in the presence of an intense, linearly polarized laser field. The polarization parameters of the emitted radiation are investigated as a function of the angle between the laser electric field and the molecular axis. The calculations are carried out by assuming a single active electron model with fixed nuclei; a two-dimensional model of the system is used. We find a different dependence of the parameters of the harmonics vs in the first or second half of the emitted spectrum. In particular, the differences are accentuated for , while for higher angles, until the perpendicular orientation, almost …
Harmonic Coupling of the Red Noise in X‐Ray Pulsars
1997
The power spectra of X-ray pulsars often show the presence of a red-noise component. This noise is produced by aperiodic variability believed to be associated with instabilities that seem to occur in accretion flows onto compact objects. In this paper we discuss how, independently of the details of the physical processes that generate these instabilities, a careful analysis of the power spectra can furnish some constraints on the distance from the stellar surface at which the sudden energy release associated with the instabilities occurs. In particular, any aperiodic variability coming from the accretion flow funneled toward the magnetic poles should be modulated at the pulsar spin period (…
High Cyclotron Harmonics Excitation in Multi-beam Terahertz Range Gyrotrons
2019
The paper presents recent results on the multi-beam gyrotrons operating at cyclotron harmonics in terahertz frequency range. The theoretical and experimental investigation of second harmonic 0.78 THz gyrotron includes comparison of generating and absorbing beam schemes, research on the effect of velocity spread and mode competition process, along with development of third harmonic 1.2 THz tube based on verified numerical codes and latest experimental results.