Generation of circularly polarized multiple high-order harmonic emission from two-color crossed laser beams

This is the publisher's version, also available electronically from http://journals.aps.org/pra/abstract/10.1103/PhysRevA.58.R2656.We present a scheme for the production of circularly polarized multiple high-order harmonic generation (HHG). The proposed experimental setup involves the use of two-color laser fields, consisting of a circularly polarized fundamental laser field and a linearly polarized second-harmonic laser field, in crossed-beam configuration. The feasibility of such a scheme is demonstrated by an ab initio quantal study of the HHG power spectrum of He atoms by means of the time-dependent density-functional theory with optimized effective potential and self-interaction correction recently developed. The theoretical study also provides insights regarding the different mechanisms responsible for the production of HHG in different energy regimes as well as the mechanism for the generation of continuous background radiation

Time-dependent density-functional theory for strong-field multiphoton processes: Application to the study of the role of dynamical electron correlation in multiple high-order harmonic generation

This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.57.452.We present a self-interaction-free time-dependent density-functional theory (TDDFT) for nonperturbative treatment of multiphoton processes of many-electron atomic systems in intense laser fields. The theory is based on the extension of the time-dependent Kohn-Sham formalism. The time-dependent exchange-correlation potential with proper short- and long-range behavior is constructed by means of the time-dependent optimized effective potential (TDOEP) method and the incorporation of an explicit self-interaction correction (SIC) term. The resulting TDOEP-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 exchange-correlation potential. We also introduce a generalized pseudospectral time-propagation method, allowing optimal spatial grid discretization, for accurate and efficient numerical solution of the TDOEP-SIC equations. The theory is applied to the study of the role of dynamical electron correlation on the multiple high-order harmonic generation (HHG) processes of He atoms in intense laser fields. We also perform a detailed study of the mechanisms responsible for the production of the higher harmonics in He atoms observed in a recent experiment that cannot be explained by the single-active-electron model. We found that both the dynamical electron correlation and the He+ ion are important to the generation of the observed higher harmonics. The present TDDFT is thus capable of providing a unified and self-consistent dynamical picture of the HHG processes

Time-dependent approach to high-resolution spectroscopy and quantum dynamics of Rydberg atoms in crossed magnetic and electric fields

This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.61.031401.We present a general time-dependent approach for efficient and accurate treatment of high-resolution spectrocopy and quantum dynamics. The procedure is applied to an ab initio time-dependent study of three-dimensional Rydberg H atoms in crossed magnetic and electric fields with spectral accuracy. Good agreement with the high-resolution experimental photoabsorption spectrum is obtained line by line, including a regime well above the Stark saddle point. We have further explored the physical origin of several unexplored perplexing phenomena in the higher-energy regime observed in the experiment

Probing the spectral and temporal structures of high-order harmonic generation in intense laser pulses

This is the published version. Also available here: http://dx.doi.org/10.1103/PhysRevA.61.021802.We present an ab initio three-dimensional quantum study of high-order harmonic generation (HHG) of atomic H in intense pulsed laser fields. Accurate time-dependent wave functions are obtained by means of the time-dependent generalized pseudospectral method recently developed and wavelet transform is used to perform time-frequency analysis of the resulting HHG power spectra. The results reveal striking details of the spectral and temporal fine structures of HHG, providing insights regarding HHG mechanisms in different energy regimes and benchmark data for testing the validity of existing HHG models

Relativistic density-functional theory with the optimized effective potential and self-interaction correction: Application to atomic structure calculations (Z=2–106)

This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.57.855.We present a self-interaction-free relativistic density-functional theory (DFT). The theory is based on the extension of our recent nonrelativistic DFT treatment with optimized effective potential (OEP) and self-interaction correction (SIC) [Phys. Rev. A 55, 3406 (1997)] to the relativistic domain. Such a relativistic OEP-SIC procedure yields an orbital-independent single-particle local potential with proper long-range Coulombic (-1/r) behavior. The method is applied to the ground-state energy calculations for atoms with Z=2–106. A comparison with the corresponding nonrelativistic OEP-SIC calculations and other relativistic calculations is made. It is shown that the ionization potentials (obtained from the highest occupied orbital energies) and individual orbital binding energies determined by the present relativistic OEP-SIC method agree well with the experimental data across the Periodic Table

Multiphoton ionization and high-order harmonic generation of He, Ne, and Ar atoms in intense pulsed laser fields: Self-interaction-free time-dependent density-functional theoretical approach

This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.64.013417.We present a detailed study of the multiphoton ionization and high-order harmonic generation (HHG) processes of rare-gas atoms (He, Ne, and Ar) in intense pulsed laser fields by means of a self-interaction-free time-dependent density-functional theory (TDDFT) recently developed. The time-dependent exchange-correlation potential with proper short- and long- range potential is constructed by means of the time-dependent optimized effective potential (TDOEP) method and the incorporation of an explicit self-interaction-correction (SIC) term. The TDOEP-SIC equations are solved accurately and efficiently by the time-dependent generalized pseudospectral technique. In this study, all the valence electrons are treated explicitly and nonperturbatively and their partial contributions to the ionization and HHG are analyzed. The results reveal instructive and qualitatively different behavior from each subshell orbital. Moreover, we found that the HHG yields from Ne and Ar atoms are considerably larger than that of the He atom in strong fields. Three main factors are identified for accounting the observed phenomena: (a) the binding energy of the subshell valence electron, (b) the orientation of the valence electron orbital (with respect to the electric-field polarization), and (c) the effect of multiphoton resonant excitation. In particular, we found that the np0 valence electrons (in Ne and Ar) with lowest binding energies and electron orbital orientation parallel to the electric-field direction, make the dominant contributions to both ionization and HHG processes in sufficiently strong fields

Density-functional theory with optimized effective potential and self-interaction correction for ground states and autoionizing resonances

This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.55.3406.We present a self-interaction-free density-functional theory (DFT) for the treatment of both the static properties of the ground states and the photoionization processes of many-electron systems. The method is based on the Krieger-Li-Iafrate (KLI) treatment of the optimized effective potential (OEP) theory and the incorporation of an explicit self-interaction correction (SIC) term. Such an extended OEP–KLI-SIC method uses only orbital-independent single-particle local potentials and is thus computationally more efficient and yet maintains good accuracy. The usefulness of the procedure is examined by the studies of the static properties of the ground states of atoms (Z⩽18) and the dynamical photoionization processes involving autoionizing resonances. Both the energy functionals of the local spin-density approximation (LSDA) and Becke's exchange energy functional and the correlation energy functional of Lee-Yang-Parr (BLYP) are used as the input to the KLI-SIC calculations. It is found that the implementation of the KLI-SIC procedure gives rise to optimized effective potentials that possess the correct behavior in both short-range and long-range regimes. As a consequence, the LSDA and BLYP ionization potentials are significantly improved. For higher-Z atoms, the improvement of the LSDA total energies and the ionization potentials are particularly remarkable, approaching the experimental or exact values. As another test of the KLI-SIC method, we have performed the calculation of the photoionization cross sections of the Ne atom using both the time-independent and time-dependent LSDA (TDLSDA) methods. We found that the TDLSDA results agree closely with the experimental data in the broad peak region, followed by a series of sharp resonances due to the 2s→np resonant transitions. The calculated linewidths and resonance line profile parameters are in reasonable agreement with both the experimental and the configuration-interaction (R-matrix) results, demonstrating the usefulness of the KLI-SIC procedure for achieving accurate DFT calculations in both static properties and dynamical processes