Quantitative Rescattering Theory for high-order harmonic generation from molecules

TL;DR

This paper introduces the Quantitative Rescattering Theory (QRS) for high-order harmonic generation in molecules, providing a framework that accurately predicts HHG spectra by combining electron wave packets with molecular photoionization data.

Contribution

The paper develops and validates the QRS model, enabling quantitative predictions of HHG spectra from molecules using laser-driven electron dynamics and molecular photoionization calculations.

Findings

QRS accurately predicts harmonic magnitude and phase for atomic targets.

QRS explains experimental HHG measurements from aligned molecules.

The model enables femtosecond dynamic imaging of molecules.

Abstract

The Quantitative Rescattering Theory (QRS) for high-order harmonic generation (HHG) by intense laser pulses is presented. According to the QRS, HHG spectra can be expressed as a product of a returning electron wave packet and the photo-recombination differential cross section of the {\em laser-free} continuum electron back to the initial bound state. We show that the shape of the returning electron wave packet is determined mostly by the laser only. The returning electron wave packets can be obtained from the strong-field approximation or from the solution of the time-dependent Schr\"odinger equation (TDSE) for a reference atom. The validity of the QRS is carefully examined by checking against accurate results for both harmonic magnitude and phase from the solution of the TDSE for atomic targets within the single active electron approximation. Combining with accurate transition dipoles obtained from state-of-the-art molecular photoionization calculations, we further show that available experimental measurements for HHG from partially aligned molecules can be explained by the QRS. Our results show that quantitative description of the HHG from aligned molecules has become possible. Since infrared lasers of pulse durations of a few femtoseconds are easily available in the laboratory, they may be used for dynamic imaging of a transient molecule with femtosecond temporal resolutions.