Angle-dependent interferences in electron emission accompanying stimulated Compton scattering from molecules

Arturo Sopena,Alicia Palacios,Fabrice Catoire,Fernando Martín,Henri Bachau

doi:10.1038/s42005-021-00749-3

Abstract

The high brilliance of ultrashort X-ray pulses recently generated in free electron lasers will soon open the way to the investigation of non-linear processes that still remain inaccessible due to the smallness of the corresponding cross sections. One of them is stimulated Compton scattering from molecules. In this work, we investigate stimulated Compton scattering from fixed-in-space H2 molecules in the few-hundred eV photon energy range, where both dipole and non-dipole transitions are important. We show that the interference between dipole and non-dipole transitions leads to pronounced asymmetries in the electron angular distributions. These asymmetries strongly depend on molecular orientation, to the point that they can lead to electron emission in either the forward or the backward directions with respect to the propagation axis, or in both directions, or even in the orthogonal direction. This is in contrast with Compton scattering from free electrons or atomic targets.

Highlights

The high brilliance of ultrashort X-ray pulses recently generated in free electron lasers will soon open the way to the investigation of non-linear processes that still remain inaccessible due to the smallness of the corresponding cross sections
Motivated by the exceptional capabilities of X-ray freeelectron laser (XFEL), in this work we have studied Compton scattering from fixed-in-space H2 molecules in the photon energy range where both A2 and A ⋅ P terms are comparable in magnitude (~500 eV)
We have calculated Molecular-frame photoelectron angular distributions (MFPADs) resulting from SCS of ~500 eV photons by hydrogen molecules

Summary

Introduction

The high brilliance of ultrashort X-ray pulses recently generated in free electron lasers will soon open the way to the investigation of non-linear processes that still remain inaccessible due to the smallness of the corresponding cross sections. At energies ~500 eV, the dipole terms, A(ri, t) ⋅ Pi, can be safely treated within the dipole approximation[7,45,46] and the nondipole terms, A2(ri, t), to first order in (k1 − k2) ⋅ ri, where k1 and k2 are the momenta of the incoming and outgoing photons, respectively, ki = ωini/c, with ni the light-incidence direction[7,8,35,44].

Results

Conclusion