Attosecond Streaking in the Water Window: A New Regime of Attosecond Pulse Characterization

TL;DR

This paper demonstrates the first attosecond streaking measurements of water-window soft X-ray pulses generated by high harmonic generation, exploring the limits of pulse characterization techniques in this new spectral regime.

Contribution

It introduces the application of attosecond streaking to water-window soft X-ray pulses and examines the challenges and fidelity issues of pulse retrieval in this regime.

Findings

Successful streaking measurement of water-window attosecond pulses

Identification of limitations in the FROGCRAB retrieval algorithm for soft X-ray pulses

Discussion of challenges in attochirp compensation and photo-ionization cross sections

Abstract

We report on the first streaking measurement of water-window attosecond pulses generated via high harmonic generation, driven by sub-2-cycle, CEP-stable, 1850 nm laser pulses. Both the central photon energy and the energy bandwidth far exceed what has been demonstrated thus far, warranting the investigation of the attosecond streaking technique for the soft X-ray regime and the limits of the FROGCRAB retrieval algorithm under such conditions. We also discuss the problem of attochirp compensation and issues regarding much lower photo-ionization cross sections compared with the XUV in addition to the fact that several shells of target gases are accessed simultaneously. Based on our investigation, we caution that the vastly different conditions in the soft X-ray regime warrant a diligent examination of the fidelity of the measurement and the retrieval procedure.