Search results for "high harmonic generation"
showing 10 items of 66 documents
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.
Orientation dependence of high-order harmonic generation in molecules
2003
We present two- and three-dimensional model calculations of high-order harmonic generation in ${\mathrm{H}}_{2}^{+}.$ The harmonic spectra exhibit clear signatures of intramolecular interference. An interference minimum appears at a harmonic order that depends on the molecular orientation. Harmonic generation in three-center molecules is studied on the basis of two-dimensional calculations for a ${\mathrm{H}}_{3}^{2+}$ model system. From analytical considerations, the orientation dependence of the harmonic intensities in three-center molecules exhibits a double minimum due to intramolecular interference. In the numerical results, the double minimum is broadened into a single wide minimum. T…
A paradigm of fullerene
2009
We study the dynamics of an electron constrained over the surface of a rigid sphere, with geometrical parameters similar to those of the C60 fullerene, embedded in a low intensity linearly polarized laser field. The model is shown to emit odd harmonics of the laser even at very low field intensity. For more intense laser fields, the spectrum presents odd harmonics and hyper-Raman lines shaped in a broad plateau. The spectrum of the model is compared to that theoretically obtained by other authors for more realistic models of C60. It is concluded that the model can be used as a paradigm for mesoscopic molecules in the fullerene family, particularly in practical applications where it is conve…
Monte Carlo Simulation of Harmonic Generation in GaAs structures operating under large-signal Conditions
2007
By using a multiparticles Monte Carlo technique, with a self-consistently coupled one-dimensional Poisson solver, we investigate the dependence of the nonlinear carrier dynamics in GaAs n+nn+ micro e submicro-structures operating under very intense sub-terahertz signals by: (i) the frequency and the intensity of the excitation signal and (ii) the length of the n region.
High-order harmonic generation in fullerenes using few- and multi-cycle pulses of different wavelengths
2012
We present the results of experimental and theoretical studies of high-order harmonic generation (HHG) in plasmas containing fullerenes using pulses of different duration and wavelength. We find that the harmonic cutoff is extended in the case of few-cycle pulses (3.5 fs, 29th harmonic) compared to longer laser pulses (40 fs, 25th harmonic) at the same intensity. Our studies also include HHG in fullerenes using 1300 and 780 nm multicycle (35 and 40 fs) pulses. For 1300 nm pulses, an extension of the harmonic cutoff to the 41st order was obtained, with a decrease in conversion efficiency that is consistent with theoretical predictions based on wave packet spreading for single atoms. Theoreti…
Dynamical effects and Terahertz harmonic generation in low-doped bulk semiconductors and submicron structures
2006
We present results obtained using a three-dimensional multivalleys Monte Carlo (MC) model to simulate the nonlinear carrier dynamics under the influence of an intense sub-terahertz electric field in a doped bulk semiconductor. By self-consistently coupling a one-dimensional Poisson solver to the ensemble MC code we simulate also the nonlinear carrier dynamics in n+nn+ structures operating under large-amplitude periodic signals and investigate the voltage-current characteristic hysteresis cycle and the high-order harmonic efficiency. For both cases we discuss the dependence of the nonlinearities and of the harmonic generation efficiency on the frequency and the intensity of the alternating s…
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.
Gouy wave modes: undistorted pulse focalization in a dispersive medium.
2007
Gouy wave modes are linear waves with finite energy that propagate without distortion at any phase and group velocity through a focal region in a dispersive medium. These features make them potentially useful for the onset and control of nonlinear interactions.