Search results for "harmonic generation"
showing 10 items of 217 documents
Strong field amplification of XUV: phase matching aspects
2011
The dependence of the yield of high-order harmonic generation (HHG) on several important experimental parameters has been successfully modeled in the last 20 years by taking into account the single atom response and propagation effects. We extended this description by adding a stimulated emission process and named it x-ray parametric amplification (XPA). Beyond the super-quadratic increase of the XUV signal, which can be explained only in a limited pressure range by HHG theory, other observed characteristics like exponential growth, gain narrowing, strong blue-shift, beam divergence, etc. and their dependence on laser intensity and gas pressure can be explained accurately only by the new XP…
Classical chaos and harmonic generation in laser driven nanorings
2016
A quantum ring driven by an intense laser field emits light in the form of high-harmonic radiation resulting from the strong acceleration experienced by the active electrons forced to move on a curved trajectory. The spectrum of the emitted light is rich and strongly dependent on the parameters of the problem. In order to investigate the physical origin of such variability, we focus on the seemingly simple problem of a laser-driven charge constrained to a ring from a classical standpoint. As it turns out, the dynamics of such a classical electron is governed by a nonlinear equation which results into a chaotic motion - by nature depending on the initial conditions in an unpredictable way. O…
Plasma emission at the laser tripled frequency
2003
The third harmonic generation in the skin-layer of a dense hot plasma due to inverse bremsstrahlung is investigated for regimes having increasing experimental relevance. New analytical dependencies of the radiation flux density at the frequency 3ω on the plasma and fundamental wave parameters are established.
Measurement of optical second-harmonic generation from an individual single-walled carbon nanotube
2013
We show that optical second-harmonic generation (SHG) can be observed from individual single-walled carbon nanotubes (SWCNTs) and, furthermore, allows imaging of individual tubes. Detailed analysis of our results suggests that the structural noncentrosymmetry, as required for SHG, arises from the non-zero chiral angle of the SWCNT. SHG thus has potential as a fast, non-destructive, and simple method for imaging of individual nanomolecules and for probing their chiral properties. Even more, it opens the possibility to optically determine the handedness of individual SWCNTs.
Monte Carlo Simulation of Electron Dynamics in Doped Semiconductors Driven by Electric Fields: Harmonic Generation, Hot-Carrier Noise and Spin Relaxa…
2011
In solid state electronics the miniaturization of integrated circuits implies that, even at moderate applied voltages, the components can be exposed to very intense electric fields. Advances in electronics push the devices to operate also under cyclostationary conditions, i.e. under large-signal and time-periodic conditions. A main consequence of this fact is that circuits exhibit a strongly nonlinear behavior. Furthermore, semiconductor based devices are always imbedded into a noisy environment that could strongly affect their performance, setting the lower limit for signal detection in electronic circuits. For this reason, to fully understand the complex scenario of the nonlinear phenomen…
Bi-color spatial solitons in linearly uncoupled planar waveguides
2004
We report on the observation of spatial optical simultons in a novel geometry consisting of two partially overlapped, linearly uncoupled planar waveguides in lithium niobate obtained by reverse proton exchange. Two orthogonally polarized modes are coupled through an off-diagonal tensor element of the quadratic nonlinearity, giving rise to second harmonic generation and mutual trapping via cascading. This phenomenon demonstrates a balance between diffraction and self-focusing for two orthogonal modes of different waveguides, and occurs at room temperature in longitudinally uniform waveguides.
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…