Stochastic modeling of x-ray superfluorescence

TL;DR

This paper develops a stochastic theoretical framework based on Maxwell-Bloch equations with noise for modeling all stages of x-ray superfluorescence, aiding interpretation and design of x-ray emission experiments.

Contribution

It introduces a first-principles derived stochastic formalism for stimulated x-ray emission, including spontaneous emission, superfluorescence, and ASE, with numerical illustrations.

Findings

The equations accurately reproduce spontaneous emission properties.

Numerical simulations show coherence and spectral characteristics of emitted x-ray fields.

The framework can interpret experimental data and guide x-ray laser development.

Abstract

An approach to modeling the dynamics of x-ray amplified spontaneous emission and superfluorescence -- the phenomenon of collective x-ray emission initiated by intense pulses of X-ray Free Electron Lasers -- is developed based on stochastic partial differential equations. The equations are derived from first principles, and the relevant approximations, derivation steps, and extensions specific to stimulated x-ray emission are presented. The resulting equations take the form of three-dimensional generalized Maxwell-Bloch equations augmented with noise terms for both field and atomic variables. The derived noise terms possess specific correlation properties that enable the correct reconstruction of spontaneous emission. Consequently, the developed theoretical formalism is universally suitable for describing all stages of stimulated x-ray emission: spontaneous emission, amplified spontaneous emission, and superfluorescence. We present numerical examples that illustrate various properties of the emitted field, including spatio-temporal coherence, spectral-angular and polarization characteristics. We anticipate that the proposed theoretical framework will establish a robust foundation for interpreting measurements in stimulated x-ray emission spectroscopy, modeling x-ray laser oscillators, and describing other experiments leveraging x-ray superfluorescence.