Quantum beats of nuclear exciton decay radiation probing single crystal Bragg scattering

The time structure and high brilliance of pulsed synchrotron radiation sources stimulate new experiments in the field of nuclear resonance fluorescence from an almost instantaneously excited nuclear ensemble. The decay radiation of this so-called nuclear exciton was used for scattering experiments from samples not containing resonance nuclei in order to study the interaction with condensed matter in the time domain. Ultrasound induced coherent rephasing of the decay radiation from two nuclear absorber targets caused phonon echo peaks and dips. Quantum beats result as a consequence of coherent (Bragg) scattering and superposition of nuclear excitons from two distant absorbers with Doppler shifted resonance energies between each other. In the case of inelastic scattering these quantum beats concentrate on the times of phonon induced echoes proving experimentally a periodic coherent rephasing of the involved decay radiation. In this article the theoretical background of such experiments will be outlined together with realistic numerical modelling of the scattering experiments. A comparison with our experimental work is also incorporated