Nuclear non-resonant photoexcitation assisted by electron recombination

TL;DR

This paper proposes a theoretical mechanism for nuclear non-resonant photoexcitation assisted by electron recombination, enabling nuclear excitation via non-resonant photons using x-ray free-electron lasers.

Contribution

It introduces a third-order process involving virtual nuclear states, distinct from electronic bridge, and explores its potential for nuclear excitation with non-resonant x-ray photons.

Findings

Calculated cross section is small but can be compensated by high photon flux.

Process demonstrated on 193Pt with a 14.2 keV transition.

Suggests new avenues for non-linear x-ray interactions mediated by nuclear states.

Abstract

We investigate theoretically a nuclear excitation mechanism involving absorption of non-resonant photons leveraged by the coupling to the atomic shell. The nuclear non-resonant photoexcitation is assisted by electron recombination which compensates the energy mismatch between photon and nuclear transition energies, reminiscent of parametric up-conversion in non-linear media. This third-order process proceeds via a virtual nuclear state rather than virtual electronic states, distinguishing this mechanism from the electronic bridge. We investigate the process on the example of a so-far not observed 14.2 keV hard x-ray transition in 193Pt driven by an x-ray free-electron laser. Although the calculated cross section is small, it can be compensated by the vast number of non-resonant photons from the x-ray laser pulse. By enabling nuclear excitation through non-resonant photons, this up-conversion-like mechanism suggests new directions for non-linear x-ray interactions mediated by nuclear transitions.