Phase distortions of attosecond pulses produced by resonance-enhanced high harmonic generation

TL;DR

This paper investigates how resonance conditions in tin plasma affect the phase and structure of attosecond pulses generated through high harmonic generation, revealing significant phase distortions and changes in pulse coherence.

Contribution

It provides the first temporal characterization of attosecond emission under near-resonant conditions in tin plasma, demonstrating the impact of resonance detuning on harmonic phase locking.

Findings

Resonance significantly alters the relative phase of neighboring harmonics.

Very small detunings can lead to loss of phase locking.

Simulations match experimental results, explaining phase distortions via the recombination dipole moment.

Abstract

Resonant enhancement of high harmonic generation can be obtained in plasmas containing ions with strong radiative transitions resonant with harmonic orders. The mechanism for this enhancement is still debated. We perform the first temporal characterization of the attosecond emission from a tin plasma under near-resonant conditions for two different resonance detunings. We show that the resonance considerably changes the relative phase of neighbouring harmonics. For very small detunings, their phase locking may even be lost, evidencing strong phase distortions in the emission process and a modified attosecond structure. These features are well reproduced by our simulations, allowing their interpretation in terms of the phase of the recombination dipole moment.