XUV yield optimization of two-color high-order harmonic generation in gases

TL;DR

This study experimentally optimizes two-color high-order harmonic generation in argon, identifying phase and intensity ratios that maximize EUV yield, and provides a predictive model based on electron return dynamics.

Contribution

It introduces a comprehensive experimental and theoretical analysis of phase and intensity ratio optimization for enhanced harmonic yield in two-color HHG.

Findings

Optimal phase and ratio for maximum yield identified

Yield enhancement varies with harmonic order and laser parameters

Predictive model for phase and ratio based on electron dynamics

Abstract

We perform an experimental two-color high-order harmonic generation study in argon with the fundamental of an ytterbium ultrashort pulse laser and its second harmonic. The intensity of the second harmonic and its phase relative to the fundamental are varied, in a large range compared to earlier works, while keeping the total intensity constant. We extract the optimum values for the relative phase and ratio of the two colors which lead to a maximum yield enhancement for each harmonic order in the extreme ultraviolet spectrum. Within the semi-classical three-step model, the yield maximum can be associated with a flat electron return time vs. return energy distribution. An analysis of different distributions allows to predict the required relative two-color phase and ratio for a given harmonic order, total laser intensity, fundamental wavelength, and ionization potential.