Search results for " generation."
showing 10 items of 1108 documents
Plasma radiation spectra in the presence of static electric and high-frequency radiation fields
2004
Harmonics generation of high-frequency radiation in a plasma embedded in a constant electric field is investigated theoretically. It is shown that the electron directed motion due to the static electric field yields the appearance in the plasma emission spectrum of high-frequency radiation even harmonics. The conditions are established when the even harmonics generation is as effective as that of the odd ones. At variance with the odd harmonics, the even harmonics polarization plane is found to rotate with respect to that of the fundamental field. The basic dependencies concerning the rotation angle and the generation efficiency on the plasma and field parameters are established.
Control of Electron Motion in a Molecular Ion: Dynamical Creation of a Permanent Electric Dipole
2007
The dynamics of a diatomic one-dimensional homonuclear molecule driven by a two-laser field is investigated beyond the usual fixed nuclei approximation. The dynamics of the nuclei is treated by means of Newton equations of motion; the full quantum description is used for the single active electron. The first laser pulse (pump) excites vibrations of the nuclei, while the second very short pulse (probe) has the role of confining the electron around one of the nuclei. We show how to use the radiation scattered in these conditions by the molecule to achieve real-time control of the molecular dynamics.
High order harmonic generation: The role of the acceleration matrix elements and of the bound and continuum transitions
2001
The electromagnetic spectrum emitted by a one-dimensional atom driven by a strong laser field is obtained by use of the acceleration form and interpreted by means of few general properties of the matrix elements of the acceleration operator. We show that the emission occurs essentially in a region near the atomic core where the acceleration is significant and we investigate the role of the various emission channels arising from interference effects between transitions involving the bare atomic levels.
The influence of the quantum nature of nuclei in high harmonic generation from H+2-like molecular ions
2013
We study the full quantum dynamics of a simple molecular ion driven by an intense laser field. In particular we show that the quantum nature of the nuclear dynamics affects the emitted high harmonic generation (HHG) spectra, strongly reshaping the plateau region. In fact, it is evident that the characteristic flat trend is transformed into a descending trend, with the lower harmonics being two orders of magnitude more intense than the higher harmonics. We show that this effect is more pronounced in the lighter isotopic species of H2+ molecular ions and we also demonstrate that in this case the contribution to HHG from the antibonding electronic energetic surface is of the same order of magn…
Fluctuating laser field that induces a blueshift in harmonic generation
1998
The spectrum of a two-level atom in the presence of a multimode laser pulse is calculated. The field is allowed to fluctuate in amplitude or in phase; the emitted spectrum has richer emission lines than in the case of the nonfluctuating field and shows peaks shifted toward the blue with respect to the traditional harmonic peaks. The position of the lines is predicted by the formula ω2n+1=(2n+1)(1+Δ)ωL with Δ being a parameter that can be found numerically. In this way the fluctuations seem to result in an effective increase of the laser frequency.
Influence of a Magnetic Field on Liquid Metal Free Convection in an Internally Heated Cubic Enclosure
2002
The buoyancy‐driven magnetohydrodynamic flow in a cubic enclosure was investigated by three‐dimensional numerical simulation. The enclosure was volumetrically heated by a uniform power density and cooled along two opposite vertical walls, all remaining walls being adiabatic. A uniform magnetic field was applied orthogonally to the gravity vector and to the temperature gradient. The Prandtl number was 0.0321 (characteristic of Pb–17Li at 300°C), the Rayleigh number was 104, and the Hartmann number was made to vary between 0 and 2×103. The steady‐state Navier–Stokes equations, in conjunction with a scalar transport equation for the fluid's enthalpy and with the Poisson equation for the electr…
Analysis of high-harmonic generation in terms of complex Floquet spectral analysis
2017
Recent developments on intense laser sources is opening a new field of optical sciences. An intense coherent light beam strongly interacting with the matter causes a coherent motion of a particle, forming a strongly dressed excited particle. A photon emission from this dressed excited particle is a strong nonlinear process causing high-harmonic generation (HHG), where the perturbation analysis is broken down. In this work, we study a coherent photon emission from a strongly dressed excited atom in terms of complex spectral analysis in the extended Floquet-Hilbert-space. We have obtained the eigenstates of the total Hamiltonian with use of Feshbach-Brilloiun-Wigner projection method. In this…
Radiative recombination in a strong laser field: low-frequency approximation
2005
A theoretical treatment of the laser-assisted radiative recombination (LARR) is presented in which the low-frequency (LF) assumption is exploited. The merit of the proposed LF approximation is twofold. First, the LF approximation considerably simplifies the calculations of the transition rates, whereas the results obtained within this approximation are only slightly different from those obtained without resorting to it. Second, the LF approximation gives more insight into the physical picture of the process, which may be viewed as a two-step process. In the first step, the free electron propagates toward the ion, and its motion is described classically with motion changes ascribed mainly to…
Modeling harmonic generation by a degenerate two-level atom
1996
An analytical theory of the generation of high-order harmonics of laser radiation has been developed on the basis of a two-level model atom with degenerate levels. Among other parameters, onset, width, and cutoff of the plateau in the harmonic spectrum are obtained in simple analytical forms that connect the basic problem parameters and permit a transparent interpretation of the mechanism underlying the spectrum formation for this specific case. Selected numerical calculations are reported to corroborate the analytical findings and to investigate other harmonic-spectrum features.
A Study of the Nuclear Structure at High Energy and Low Spin
1983
A novel method to study nuclear structure at low spin as a function of temperature is developed and used on 146,148Sm, 154,156Gd and 160,162Dy, by means of the (3He, α) reaction. The nuclear level density for a wide energy range is also studied. The γ-multiplicities and the first generation γ-ray spectra indicate a structure change in deformed nuclei at about 6 MeV.