Subcycle phase matching effects in short attosecond pulse trains

TL;DR

This paper investigates how subcycle phase matching influences the spectral and temporal properties of attosecond pulse trains generated by high-order harmonic generation, revealing complex effects that go beyond single-atom responses.

Contribution

It demonstrates the role of time-dependent phase matching in shaping attosecond pulse trains using two-color laser-assisted photoionization, providing new insights into HHG dynamics.

Findings

Spectral behavior varies with carrier-to-envelope phase shifts.

Time-dependent phase matching affects pulse train structure.

Two-color photoionization reveals subcycle phase effects.

Abstract

Attosecond pulses produced by High-order Harmonic Generation (HHG) in gases driven by intense laser fields have become a cornerstone technique for probing ultrafast electronic motion in matter. These applications require a good knowledge of the temporal and spectral properties of the emitted radiation. In this work, we generate a train of two to three attosecond pulses that we characterize using two-color laser-assisted photoionization. \textcolor{black}{An unexpected spectral behavior, with more pulses at high energies than at low energies, is observed when the carrier-to-envelope phase of the laser field is changed by 90$^\circ$.} HHG simulations indicate that the time-dependent phase matching of the harmonics contributes in a non-trivial way to the structure of the pulse train. Two-color laser-assisted photoionization enables us to unravel the dynamical influence of subcycle phase matching on the spectral properties of the attosecond pulse train, going beyond the predictions of the response of a single atom to a strong laser field.