Classical, semi-classical and quantum optical models for x-ray planar cavity with electronic resonance

TL;DR

This paper develops semi-classical and quantum models for x-ray planar cavities with electronic resonances, providing analytical tools to interpret experimental phenomena and optimize cavity designs for advanced x-ray spectroscopy.

Contribution

It introduces two new theoretical models, semi-classical matrix and quantum Green's function, for analyzing x-ray cavities with electronic resonances, validated against classical methods.

Findings

Good agreement between models and classical results

Models can interpret cavity effects like decay rate and energy shift

Framework aids future experimental design and quantum optical studies

Abstract

Here two theoretical models of semi-classical matrix and quantum Green's function are developed for the system of x-ray thin-film planar cavity with inner-shell electronic resonances. The semi-classical model is based on the matrix formalism to treat each layer as the propagating matrix. The crucial idea is to expand the propagating matrix of the resonant atomic layer under ultrathin-film approximation, then derive the analytical expression of the spectral observation, i.e, the cavity reflectance. The typical cavity effects of cavity enhanced decay rate, cavity induced energy shift and the Fano interference which were observed in the recent experiments could be phenomenologically interpreted. The second quantum model employs the analytical Green's function to solve the cavity system. The system Hamiltonian and the effective energy-level are derived. The effective energy-level scheme indicates that the cavity effect acts on the regulation of the intermediated core-hole state. To test the validity of the semi-classical matrix and quantum Green's function models, the classical Parratt's formalism and the dispersion correction of the atomic refractive index are also recalled. Very good agreements in reflectivity spectra between semi-classical and quantum models with the Parratt's results are observed. The present semi-classical matrix and quantum Green's function models will be useful to predict the new phenomena and optimize the cavity structures for future experiments and promote the emerging of quantum optical effects with modern x-ray spectroscopy techniques.