Superradiance of an ensemble of nuclei excited by a free electron laser

Abstract

In 1954 Dicke predicted the accelerated initial decay of multiple atomic excitations 1 , laying the foundation for the concept of superradiance. Further studies 2-4 suggested that emission of the total energy was similarly accelerated, provided that the system reaches the inversion threshold. Superradiant emission of the total energy has been confirmed by numerous studies [4][5][6][7][8][9][10][11][12] , yet the acceleration of the initial decay has not been experimentally demonstrated. Here we use resonant diffraction of X-rays from the Mössbauer transition 13 of 57 Fe nuclei to investigate superradiant decay, photon by photon, along the entire chain of the de-excitation cascade of up to 68 simultaneous coherent nuclear excitations created by a pulse of an X-ray free-electron laser. We find agreement with Dicke's theory 1 for the accelerated initial decay as the number of excitations is increased. We also find that our results are in agreement with a simple statistical model, providing a necessary baseline for discussing further properties of superradiance, within and beyond the low-excitation regime. Dicke's model introduces superradiance as an accelerated initial decay of multiple atomic excitations, and provides exact predictions for the ensemble behaviour as a function of the number of atoms and number of excitations in the system

Superfluorescence, Free-Induction Decay, and Four-Wave Mixing: Propagation of Free-Electron Laser Pulses through a Dense Sample of Helium Ions

“…We interpret our findings (see figure 1) as cascade superfluorescence (469 nm and 164 nm), yoked superfluorescence (30.4 nm), and free-induction decay (25.6 nm and 24.3 nm). To our knowledge superfluorescence at such short wavelengths has not been reported previously, although recently few-photon superradiance has been observed at X-ray wavelengths [8,10].…”

Resonating valence bonds and spinon pairing in the Dicke model

“…In contrast, the spin-photon coupling was much weaker than the cavity loss rate (43 MHz), as required by (c). Similar parameters are potentially achievable in other systems such as cold gases [15,31], ion traps [32], diamond with nitrogen-vacancies [33] and nuclear ensembles [34]. RVB character of collapsed states can be ascertained by measuring spin-spin correlations, which can be worked out from our explicit wavefunctions.…”

Nuclear excitation by electron capture in optical-laser-generated plasmas

“…Note that due to our approach for the potential lowering there might appear additional NEEC capture channels at low resonance energies (e.g. for the weak-coupling limit, i.e., (a/λ D ) 3 1 , and…”

“…Covering several frequency scales, intense coherent light sources available today open unprecedented possibilities for the field of laser-matter interactions [2] also beyond atomic physics. Novel x-ray sources as the X-ray Free Electron Laser (XFEL) open for instance new possibilities to drive low-lying electromagnetic transitions in nuclei [3]. On the other hand, high-power optical lasers with their tremendous efficiency in transferring kinetic energy to charged particles may cause formation of plasma [4], the host of complex interactions between photons, electrons, ions and the atomic nucleus.…”