High-order Harmonic Spectroscopy of the Cooper Minimum in Argon: Experimental and Theoretical Study

TL;DR

This paper investigates the Cooper minimum in argon high harmonic generation using experimental measurements and a semi-classical theoretical model, revealing shifts caused by electron dynamics and polarization effects.

Contribution

It combines experimental data with the CTMC-QUEST model to explain the observed shifts in the Cooper minimum in high harmonic spectra.

Findings

The harmonic minimum is shifted relative to photoionization measurements.

Electron directivity and polarization influence the harmonic emission.

Wavepacket shape affects the observed spectral features.

Abstract

We study the Cooper minimum in high harmonic generation from argon atoms using long wavelength laser pulses. We find that the minimum in high harmonic spectra is systematically shifted with respect to total photoionization cross section measurements. We use a semi-classical theoretical approach based on Classical Trajectory Monte Carlo and Quantum Electron Scattering methods (CTMC-QUEST) to model the experiment. Our study reveals that the shift between photoionization and high harmonic emission is due to several effects: the directivity of the recombining electrons and emitted polarization, and the shape of the recolliding electron wavepacket.