Spatially and spectrally resolved quantum path interference with chirped driving pulses

TL;DR

This paper investigates high-order harmonic generation in argon using chirped laser pulses, revealing detailed interference patterns and extracting phase parameters for different electron trajectories through experimental and theoretical analysis.

Contribution

It introduces a method to analyze spatially and spectrally resolved interference in high-order harmonics using chirped pulses, providing new insights into electron trajectory phases.

Findings

Observation of off-axis and on-axis interference structures.

Extraction of dipole phase parameters for short and long trajectories.

Agreement of experimental results with Schrödinger equation calculations.

Abstract

We measure spectrally and spatially resolved high-order harmonics generated in argon using chirped multi-cycle laser pulses. Using a stable, high-repetition rate laser we observe detailed interference structures in the far-field. The structures are of two kinds; off-axis interference from the long trajectory only and on-axis interference including the short and long trajectories. The former is readily visible in the far-field spectrum, modulating both the spectral and spatial profile. To access the latter, we vary the chirp of the fundamental, imparting different phases on the different trajectories, thereby changing their relative phase. Using this method together with an analytical model, we are able to explain the on-axis behaviour and access the dipole phase parameters for the short (\(\alpha_s\)) and long (\(\alpha_l\)) trajectories. The extracted results compare very well with phase parameters calculated by solving the time-dependent Schr\"odinger equation. Going beyond the analytical model, we are also able to successfully reproduce the off-axis interference structure.