Stimulated X-ray Raman scattering in Free Electron Lasers with incoherent spectrum

TL;DR

This paper investigates stimulated X-ray Raman scattering in SASE free electron lasers with incoherent spectra, showing that high-intensity x-ray pulses can induce transitions in atoms and potentially narrow the FEL spectrum.

Contribution

It introduces a theoretical analysis of stimulated Raman scattering effects in incoherent FEL spectra and suggests a method to modify and narrow the FEL output spectrum.

Findings

High transition probabilities at $10^{20}$ W/cm$^2$ intensities.

Potential to use this effect to narrow FEL spectra.

Theoretical calculation of transition rates in a three-level system.

Abstract

The single-pulse spectrum of self-amplified spontaneous emission (SASE) free electron lasers (FELs) is characterized by random fluctuations in frequency. The typical spectrum bandwidth for a hard x-ray FEL is in the range of 10-20 eV and is comparable with the distance between energy levels of valence electrons in atoms an molecules. We calculate the rate of transitions in a quantum three-level system with the energy difference of several eV caused by such radiation and show that for x-ray intensities in the range of $10^{20}$ W/cm$^2$ the probability of the transition over the duration of the x-ray pulse is large. We argue that this effect can be used to modify the spectrum of a SASE FEL potentially making it more narrow.