Femtosecond profiling of shaped X-ray pulses

TL;DR

This paper demonstrates femtosecond-resolved characterization of shaped X-ray pulses at a free-electron laser, enabling precise control and future pulse shaping techniques.

Contribution

It introduces a method to directly measure and characterize shaped X-ray pulses with femtosecond resolution using photoelectron streaking spectroscopy.

Findings

Successful generation of X-ray pulse pairs with variable properties

Single-shot femtosecond characterization of X-ray pulses

Advancement towards precise X-ray pulse shaping techniques

Abstract

Arbitrary manipulation of the temporal and spectral properties of X-ray pulses at free-electron lasers (FELs) would revolutionize many experimental applications. At the Linac Coherent Light Source at Stanford National Accelerator Laboratory, the momentum phase-space of the FEL driving electron bunch can be tuned to emit a pair of X-ray pulses with independently variable photon energy and femtosecond delay. However, while accelerator parameters can easily be adjusted to tune the electron bunch phase-space, the final impact of these actuators on the X-ray pulse cannot be predicted with sufficient precision. Furthermore, shot-to-shot instabilities that distort the pulse shape unpredictably cannot be fully suppressed. Therefore, the ability to directly characterize the X-rays is essential to ensure precise and consistent control. In this work, we have generated X-ray pulse pairs and characterized them on a single-shot basis with femtosecond resolution through time-resolved photoelectron streaking spectroscopy. This achievement completes an important step toward future X-ray pulse shaping techniques.