Abstract
The resonant interaction between x-ray photons and nuclei is one of the most exciting subjects of the burgeoning field of x-ray quantum optics. A resourceful platform used so far are thin-film x-ray cavities with embedded layers or M\"ossbauer nuclei such as $^{57}\mathrm{Fe}$. A new quantum optical model based on the classical electromagnetic Green's function is developed to investigate theoretically the nuclear response inside the x-ray cavity. The model is versatile and provides an intuitive picture about the influence of the cavity structure on the resulting spectra. We test its predictive powers with the help of the semiclassical coherent scattering formalism simulations and discuss our results for increasing complexity of layer structures.
Highlights
Compared to optical photons, x rays have a number of desirable properties such as deeper penetration, better focus, no limitation by an inconvenient diffraction limit as for low-frequency photons, and correspondingly superior spatial resolution, as well as robustness, and the large momentum transfer they may produce
Particular features which are well reproduced by the model are highlighted and physical interpretations are presented
The advantages of the formalism are its versatility and the fact that it only requires one fit parameter, which solely depends on the nuclear layer thickness and composition
Summary
X rays have a number of desirable properties such as deeper penetration, better focus, no limitation by an inconvenient diffraction limit as for low-frequency photons, and correspondingly superior spatial resolution, as well as robustness, and the large momentum transfer they may produce. More concretely for the case of thin-film cavities, semiclassical methods such as the Parratt formalism [29] or the layer formalism [30] implemented in the software package CONUSS [31,32] have proven to be very successful in modeling experimental data [6,7,8,9,11,12,13] This is remarkable considering that so far the low intensity of synchrotron radiation sources allows mostly single resonant x-ray photons to couple to the Mössbauer nuclei in the cavity. The model is not restricted to single excitations and is useful for future applications involving XFEL light As it accounts for the quantization of the field, the model can be used to investigate the quantum properties of x-ray photons, for instance, via higher-order correlation functions.
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