Study of high-order harmonic generation in xenon based on time-dependent density-functional theory

Abstract

The high-order harmonic generation (HHG) in xenon is studied by using the time-dependent density-functional theory. The dynamics of all electrons on the outer 4th and 5th atomic shells is considered with subsequent separation of contributions of different atomic orbitals to the HHG amplitude. It is shown that giant enhancement of HHG yield in a spectral region near 100 eV is caused by perturbation of the electron–electron interaction potential induced by recolliding photoelectron wavepacket originated from the 5p 0 orbital. This perturbation leads to the collective oscillations of all orbitals on the 4th shell closely localized in space and strongly interacting with each other. The resulting HHG yield is enhanced by more than an order of magnitude compared with the response of the single 5p 0 orbital. The high accuracy of the numerical results is confirmed by comparing the calculated HHG spectra and photoionization cross-sections with experimental results and an analytical parameterization of the HHG yield.

Simulation of High Harmonic Generation in Xenon Based on Time-Dependent Density-Functional Theory

“…It can be seen from the figures that in the low-frequency region (slightly above the ionization potential I p = 12.1 eV), the calculated HHG spectra contain a narrow near-threshold enhancement region. As shown in [11], this enhancement is associated with a sharp increase of the recombination transition matrix element from the continuum state to the 5p 0 state with decreasing frequency of emitted photons. At harmonic frequencies below I p , the SAE approximation significantly overestimates the spectral intensity (up to one order of magnitude) compared to TDDFT (there are no experimental data for this range).…”

“…The giant enhancement is a result of the giant dipole resonance in the photoelectron recombination cross-section with a maximum near 100 eV due to the correlation of the photoelectron with inner orbitals [5,20,21]. In the TDKS equations, this enhancement is provided by the orbitals response from the 4th shell, caused by the perturbation of the electron-electron interaction potential induced by recolliding photoelectron wavepacket originating from the 5p 0 orbital [11]. The giant enhancement is not observed in the results of the SAE approximation, which does not take into account multielectron dynamics.…”

“…The algorithm for the numerical solution of TDKS equations ( 2) is based on the expansion of wave functions in spherical harmonics and was well described in Refs. [3,11,15,16]. To speed up numerical calculations, we use a nonuniform spatial grid, which has a higher density of nodes near the nucleus.…”

“…In this work, we discuss an implementation of the time-dependent density functional theory (TDDFT) for the simulation of HHG in Xe atoms in intense laser fields. A more detailed analysis of HHG in Xe (including analytical description and calculations of contributions of different atomic orbitals) can be found in our recent article [11]. Here, we provide additional calculations for different laser pulse intensities, carrier-envelope phases (CEPs) and compare the results with the single-active electron (SAE) approximation and experiment [4].…”

“…An example of the large influence of multielectron dynamics at the recombination step consists in the giant enhancement of HHG yield in xenon. This enhancement is associated with the interaction of the photoelectron, originating from the external 5p 0 orbital, with the inner electrons of the atom [4][5][6][7][8][9][10][11]. The giant enhancement in the HHG spectrum was predicted in [5] based on the analytical parametrization of the HHG spectrum in terms of the electron wave packet and the differential photorecombination cross section [12].…”