Chirped seeded free-electron lasers: self-standing light sources for two-colour pump-probe experiments

TL;DR

This paper introduces a novel regime for free-electron lasers triggered by chirped laser pulses, enabling independent control of two spectral components for advanced two-colour pump-probe experiments in the VUV/X-ray range.

Contribution

It demonstrates a new dynamical regime for free-electron lasers using chirped seed pulses, allowing independent control of dual pulses for pump-probe applications.

Findings

Theoretical model matches experimental results.

Dual pulses with controllable spectral and temporal separation.

Potential for advanced two-colour spectroscopy in VUV/X-ray domain.

Abstract

We demonstrate the possibility to run a single-pass free-electron laser in a new dynamical regime, which can be exploited to perform two-colour pump-probe experiments in the VUV/X-ray domain, using the free-electron laser emission both as a pump and as a probe. The studied regime is induced by triggering the free-electron laser process with a powerful laser pulse, carrying a significant and adjustable frequency chirp. As a result, the emitted light is eventually split in two sub-pulses, whose spectral and temporal separations can be independently controlled. We provide a theoretical description of this phenomenon, which is found in good agreement with experiments performed on the FERMI@Elettra free-electron laser.