Quantum mechanical approach to probing the birth of attosecond pulses using a two-color field

TL;DR

This paper presents a quantum mechanical theoretical approach to understanding the birth of attosecond pulses by analyzing harmonic generation in a two-color laser field, aligning well with experimental observations.

Contribution

It introduces a saddle-point based quantum model to analyze harmonic phase variations and their relation to attosecond pulse group delay.

Findings

Phase variation of even harmonics matches experimental data.

The phase-delay relationship depends on laser intensity, wavelength, and atomic ionization potential.

The model provides insights into controlling attosecond pulse generation.

Abstract

We investigate the generation of even and odd harmonics using an intense laser and a weak second harmonic field. Our theoretical approach is based on solving the saddle-point equations within the Strong Field Approximation. The phase of the even harmonic oscillation as a function of the delay between fundamental and second harmonic field is calculated and its variation with energy is found to be in good agreement with recent experimental results. We also find that the relationship between this phase variation and the group delay of the attosecond pulses, depends on the intensity and wavelength of the fundamental field as well as the ionization potential of the atom.