Continuous spectra in high-harmonic generation driven by multicycle laser pulses

TL;DR

This paper demonstrates how to generate XUV continua using multicycle laser pulses in high harmonic generation by controlling pulse chirp and phase matching, enabling coherent synthesis without isolated attosecond bursts.

Contribution

It introduces a method to produce XUV continua with multicycle pulses through phase and chirp control, expanding capabilities for attosecond pulse shaping.

Findings

XUV continua achieved in 20-37 eV range

Negative chirp and phase matching are crucial

Continuum results from microscopic and macroscopic effects

Abstract

We present observations of the emission of XUV continua in the 20-37 eV region by high harmonic generation (HHG) with $4$-$7\ \mathrm{fs}$ pulses focused onto a Kr gas jet. The underlying mechanism relies on coherent control of the relative delays and phases between individually generated attosecond pulse, achievable by adjusting the chirp of the driving pulses and the interaction geometry. Under adequate negative chirp and phase matching conditions, the resulting interpulse interference yields a continuum XUV spectrum, which is due to both microscopic and macroscopic (propagation) contributions. This technique opens the route for modifying the phase of individual attosecond pulses and for the coherent synthesis of XUV continua from multicycle driving laser pulses without the need of an isolated attosecond burst.