High harmonic generation

About: High harmonic generation is a research topic. Over the lifetime, 11694 publications have been published within this topic receiving 222650 citations. The topic is also known as: HHG.

Harmonic Generation with Ideal Rectifiers

Abstract: It is shown that the nth harmonic cannot be generated with an efficiency exceeding 1/n2. Of the power converted to dc and harmonics, at least 75 per cent is dc dissipation, and this cannot be reduced by an arrangement of selective circuits.

Self-interaction-free time-dependent density-functional theory for molecular processes in strong fields: High-order harmonic generation of H 2 in intense laser fields

Abstract: We present a self-interaction-free time-dependent density-functional theory (TDDFT) for nonperturbative treatment of multiphoton processes of many-electron molecular systems in intense laser fields. The time-dependent exchange-correlation (xc) energy potential with proper short- and long-range potential is constructed by means of the time-dependent optimized effective potential (OEP) method and the incorporation of an explicit self-interaction-correction (SIC) term. The resulting time-dependent OEP/SIC equations are structurally similar to the time-dependent Hartree-Fock equations, but include the many-body effects through an orbital-independent single-particle local time-dependent xc potential. A numerical time-propagation technique is introduced for accurate and efficient solution of the TDDFT/OEP-SIC equations for two-center diatomic molecular systems. This procedure involves the use of a generalized pseudospectral method for nonuniform optimal grid discretization of the Hamiltonian in prolate spheroidal coordinates and a split-operator scheme in the energy representation for the time development of the electron orbital wave functions. High-precision time-dependent wave functions can be obtained by this procedure with the use of only a modest number of spatial grid points. The theory is applied to a detailed study of high-order harmonic generation (HHG) processes of ${\mathrm{H}}_{2}$ molecules in intense pulsed laser fields. Particular attention is paid to the exploration of the spectral and temporal structures of HHG by means of the wavelet time-frequency analysis. The results reveal striking details of the spectral and temporal fine structures of HHG, providing new insights regarding the detailed HHG mechanisms in different energy regimes.

Effects of multiple electronic shells on strong-field multiphoton ionization and high-order harmonic generation of diatomic molecules with arbitrary orientation: An all-electron time-dependent density-functional approach

Abstract: We present a time-dependent density-functional theory approach with proper long-range potential for an ab initio study of the effect of correlated multielectron responses on the multiphoton ionization (MPI) and high-order harmonic generation (HHG) of diatomic molecules ${\text{N}}_{2}$ and ${\text{F}}_{2}$ in intense short laser pulse fields with arbitrary molecular orientation. We show that the contributions of inner molecular orbitals to the total MPI probability can be sufficiently large or even dominant over the highest-occupied molecular orbital, depending on detailed electronic structure and symmetry, laser field intensity, and orientation angle. The multielectron effects in HHG are also very important. They are responsible for enhanced HHG at some orientations of the molecular axis. Even strongly bound electrons may have a significant influence on the HHG process.

Properties of an electron in a quantum double well driven by a strong laser: Localization, low-frequency, and even-harmonic generation.

Abstract: We study how a strong semi-infinite laser pulse affects an electron confined by a potential whose parameters mimic an AlAs-GaAs-AlAs double quantum well. Interesting phenomena take place for special values of laser frequency, intensity, and pulse rise time. There are values of these parameters for which the dipole moment of the system has a low-frequency Fourier component whose magnitude is higher than that of the fundamental (i.e., the component having the same frequency as the laser). For other parameter values, the low-frequency component disappears and the Fourier transform of the dipole moment has a large zero-frequency component and intense even-harmonic components (i.e., with frequency 2n\ensuremath{\omega}, where n is an integer and \ensuremath{\omega} is the laser frequency). The presence of the even harmonics is intriguing: The system has inversion symmetry and even harmonics are forbidden by symmetry rules valid to all orders in perturbation theory. Finally, a laser pulse with well-chosen parameters can drive an electron that was initially in a delocalized eigenstate, to a state in which it is almost completely localized in one well. These processes are systematically investigated by numerical calculations and are rationalized with the help of a simple model which predicts the qualitative behavior observed numerically. The model suggests that these phenomena occur at those values of the parameters for which two Floquet states having different generalized parities become degenerate or nearly degenerate. This condition is rather general and we see no reason why it will not be fulfilled in systems other than double quantum wells (e.g., atoms or molecules).