Phase-matched high-order harmonic generation in pre-ionized noble gases

TL;DR

This paper introduces a novel pre-ionization technique using a weak capillary discharge to improve phase-matching in high-order harmonic generation, significantly enhancing efficiency in long gas targets.

Contribution

The study demonstrates, for the first time, phase-matched high-order harmonic generation in pre-ionized noble gases using a capillary discharge, supported by analytical and numerical models.

Findings

Successful demonstration in argon and krypton gases

Enhanced harmonic generation efficiency

Validated phase-mismatch control through models

Abstract

One of the main difficulties to efficiently generating high-order harmonics in long neutral-gas targets is to reach the phase-matching conditions. One issue is that the medium cannot be sufficiently ionized by the driving laser due to plasma defocusing. We propose a method to improve the phase-matching by pre-ionizing the gas using a weak capillary discharge. We have demonstrated this mechanism, for the first time, in absorption-limited XUV generation by an 800 nm femtosecond laser in argon and krypton. The phase-mismatch control ability of our method is confirmed by an analytical model and numerical simulation of the complete generation process. Our method allows increasing the efficiency of the harmonic generation significantly, paving the way towards photon-hungry applications of these short-wavelength compact sources.