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 f luorescence from an almost instantaneously excited nuclear ensemble. T he decay radiation of this so-called nuclear exciton was used for scat tering experiments from samples not containing resonance nuclei in ord er 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 be ats result as a consequence of coherent (Bragg) scattering and superpo sition of nuclear excitons from two distant absorbers with Doppler shi fted resonance energies between each other. In the case of inelastic s cattering these quantum beats concentrate on the times of phonon induc ed echoes proving experimentally a periodic coherent rephasing of the involved decay radiation. In this article the theoretical background o f such experiments will be outlined together with realistic numerical modelling of the scattering experiments. A comparison with our experim ental work is also incorporated. (C) 1998 Elsevier Science B.V. All ri ghts reserved.