Classical effect for enhanced high harmonic yield in ultrashort laser pulses with a moderate laser intensity

TL;DR

This study reveals that shorter ultrashort laser pulses enhance high harmonic generation efficiency even at moderate intensities, primarily due to classical electron rescattering effects, and can be further amplified with two-color laser fields.

Contribution

The paper uncovers a classical effect that boosts HHG efficiency in moderate laser intensities and demonstrates how two-color fields can significantly amplify this effect.

Findings

Shorter pulses increase HHG efficiency at moderate intensities.

Classical electron rescattering distance influences HHG yield.

Two-color laser fields amplify the classical effect.

Abstract

We study the influence of the pulse duration on high harmonic generation (HHG) with exploring a wide laser-parameter region theoretically. Previous studies have showed that for high laser intensities near to the saturation ionization intensity, the HHG inversion efficiency is higher for shorter pulses since the ground-state depletion is weaker in the latter. Surprisingly, our simulations show this high efficiency also appears even for a moderate laser intensity at which the ionization is not strong. A classical effect relating to shorter travel distances of the rescattering electron in shorter pulses, is found to contribute importantly to this high efficiency. The effect can be amplified significantly as a two-color laser field is used, suggesting an effective approach for increasing the HHG yield.