Tunable sub-luminal propagation of narrowband x-ray pulses

TL;DR

This paper demonstrates tunable sub-luminal propagation of narrowband x-ray pulses by controlling group velocity through a steep positive dispersion in a nuclear resonant medium, confirmed by direct temporal delay measurements.

Contribution

It introduces a method to control x-ray pulse group velocity using nuclear resonances in a cavity, enabling sub-luminal propagation with direct delay measurement.

Findings

Achieved sub-luminal x-ray pulse propagation at 14.4 keV.

Demonstrated control of group velocity via nuclear resonance dispersion.

Experimental results agree with theoretical predictions.

Abstract

Group velocity control is demonstrated for x-ray photons of 14.4 keV energy via a direct measurement of the temporal delay imposed on spectrally narrow x-ray pulses. Sub-luminal light propagation is achieved by inducing a steep positive linear dispersion in the optical response of ${}^{57}$Fe M\"ossbauer nuclei embedded in a thin film planar x-ray cavity. The direct detection of the temporal pulse delay is enabled by generating frequency-tunable spectrally narrow x-ray pulses from broadband pulsed synchrotron radiation. Our theoretical model is in good agreement with the experimental data.