Investigation of radiative coupling and of enlarged decay rates of nuclear oscillators -: art. no. 043810

The nuclear forward scattering of synchrotron radiation (SR) of two spatially separated stainless-steel foils has been investigated. Immediately after the SR pulse a nuclear exciton extending over both targets is formed, which then decays under the influence of radiative coupling of the nuclear oscillators both within and between the targets. Cooling one target to low temperatures causes the Mossbauer linewidth to increase by inhomogeneous broadening. which leads to a rapid dephasing of the nuclear oscillators of this system. In general, the influence of the radiation field of the upstream oscillators on the oscillators of the downstream target causes the latter to radiate at a high decay rate (steep slope) at early times. Surprisingly, for the combined targets, the initial decay can be less steep than that of the inhomogeneously broadened sample alone if this broadening is sufficiently large. In addition, when the upstream oscillators are broadened in energy they may cause the downstream oscillators to emit only very little intensity at late times. In the experiments, this influence on the downstream sample was changed by varying the inhomogeneous resonance broadening and the resonance frequencies of the targets. Drastic changes of the time evolution of the nuclear forward scattering were observed, which are discussed within the dynamical theory.