Simulation of nonlinear Compton scattering from bound electrons

TL;DR

This paper presents a simulation method for nonlinear Compton scattering from bound electrons, investigating the role of binding energy and electron correlations, and finds no additional redshift beyond free-electron predictions.

Contribution

It introduces a simulation approach for bound electron nonlinear Compton scattering and analyzes the effects of binding energy and electron correlations on frequency shifts.

Findings

No extra redshift beyond free-electron model predictions.

Small blue-shift observed relative to free-electron predictions.

Electron-electron correlations unlikely cause of the redshift.

Abstract

Recent investigations by Fuchs et al. [Nat. Phys. 11, 964 (2015)] revealed an anomalous frequency shift in non-linear Compton scattering of high-intensity X-rays by electrons in solid beryllium. This frequency shift was at least 800 eV to the red of the values predicted by analytical free-electron models for the same process. In this paper, we describe a method for simulating non-linear Compton scattering. The method is applied to the case of bound electrons in a local, spherical potential to explore the role of binding energy in the frequency shift of scattered X-rays for different scattered angles. The results of the calculation do not exhibit an additional redshift for the scattered X-rays beyond the non-linear Compton shift predicted by the free-electron model. However, it does reveal a small blue-shift relative to the free electron prediction for non-linear Compton scattering. The effect of electron-electron correlation effects is calculated and determined to be unlikely to be the source of the redshift. The case of linear Compton scattering from a photoionized electron followed by electron recapture is examined as a possible source of the redshift and ruled out.