Fine-scale oscillations in the wavelength- and intensity-dependence of high-harmonic generation: connection with channel closings

TL;DR

This paper explores the fine-scale oscillations in high-harmonic generation yield related to wavelength and intensity, linking them to channel closing effects and quantum interference, with insights into the influence of atomic potential tails.

Contribution

It identifies the quantum interference origin of oscillations in HHG and reveals the impact of the Coulomb tail on peak positions, challenging previous short-range potential models.

Findings

Oscillations are due to quantum interference of rescattering trajectories.

Peaks are shifted away from the channel closing condition.

Long Coulomb tail causes the observed shift in peak positions.

Abstract

We investigate the connection of recently identified fine-scale oscillations in the dependence of the yield of the high-harmonic generation (HHG) on wavelength lambda of a few-cycle laser pulse [K. Schiessl, K.L. Ishikawa, E. Persson, and J. Burgdorfer, Phys. Rev. Lett. 99, 253903 (2007)] to the well-known channel closing (CC) effect. Using the Lewenstein model of HHG, we identify the origin of the oscillations as quantum interference of many rescattering trajectories. By studying the simultaneous variations with intensity and wavelength, different models for the interference of channel closing peaks can be tested. Contrary to theoretical predictions for short-range potentials, the peaks are not located neither at nor just below the CC condition, but a significant shift is observed. The long Coulomb tail of the atomic potential is identified as the origin of the shift.