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Semi-classical wavefunction model for high-harmonic generation

Focus

A time-domain semi-classical wavefunction model can explain the frequency-domain factorization of the high-harmonic generation spectrum.
High-harmonic generation (HHG) – the process by which a gas of atoms or molecules irradiated by an intense laser pulse emits a broad spectrum of extreme ultraviolet radiation – has long been considered a promising avenue to probe the structure and dynamics of matter at the electronic scale. Such techniques are referred to as high-harmonic spectroscopy (HHS). By nature, HHG and HHS live in the spectral domain while the laser-induced dynamics takes place in the temporal domain. This difference of frames presents a challenge for probing time-dependent phenomena through HHS. In this paper, we introduce a semi-classical wavefunction model and use it to build a bridge between the time and frequency domains. For instance, applied to HHG, it explains the factorization of the HHG spectra into ionization, propagation and recollision steps, as is observed in the quantitative rescattering (QRS) formalism.

Associated publications

Semiclassical modeling of high-order harmonic generation driven by an elliptically polarized laser field: the role of recolliding periodic orbits

posted Jan 18, 2017, 6:14 PM by François Mauger   [ updated Jan 18, 2017, 6:15 PM ]

Abstract

We model high-order harmonic generation (HHG) from an argon atom driven by an elliptically polarized laser field, using classical electron trajectories that are initialized from a discrete set of microcanonical distributions. Analysis of the returning trajectories reveals that when the atomic potential is accounted for, there are two possible ionization pathways leading to the same photon energy for both the short and the long trajectories found in the recollision model of HHG. We also demonstrate that the threshold ellipticity, a measure of the sensitivity to ellipticity, decreases as the harmonic order increases for both short and long trajectories, in qualitative agreement with recent experimental results (Larsen et al 2015 arXiv:1506.08660). We use a nonlinear dynamical analysis to show that this behavior is regulated by a set of recolliding periodic orbits (RPOs) that survive at ellipticities greater than 0.2 and can therefore drive the recollision dynamics even at relatively high ellipticity. The connection between the threshold ellipticity dependence we find and RPOs means that the effect should be general.

Reference

P.M. Abanador, F. Mauger, K. Lopata, M.B. Gaarde, and K.J. Schafer - Semiclassical modeling of high-order harmonic generation driven by an elliptically polarized laser field: the role of recolliding periodic orbits - Journal of Physics B 50, 035601 (2017)

Semiclassical-wave-function perspective on high-harmonic generation

posted May 13, 2016, 10:31 PM by François Mauger   [ updated May 13, 2016, 11:09 PM ]

Abstract

We introduce a semiclassical-wave-function (SCWF) model for strong-field physics and attosecond science. When applied to high-harmonic generation (HHG), this formalism allows one to show that the natural time-domain separation of the contribution of ionization, propagation, and recollisions to the HHG process leads to a frequency domain factorization of the harmonic yield into these same contributions, for any choice of atomic or molecular potential. We first derive the factorization from the natural expression of the dipole signal in the temporal domain by using a reference system, as in the quantitative rescattering (QRS) formalism [J. Phys. B 43, 122001 (2010)]. Alternatively, we show how the trajectory component of the SCWF can be used to express the factorization, which also allows one to attribute individual contributions to the spectrum to the underlying trajectories.

Reference

F. Mauger, P.M. Abanador, K. Lopata, K.J. Schafer, and M.B. Gaarde - Semiclassical-wave-function perspective on high-harmonic generation - Physical Review A 93, 043815 (2016)

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