Laser-Matter Interaction: Classical Regime versus Quantum Regime
  Doppler backscattering of optical laser photons on a "flying mirror" of relativistic electrons promises to yield coherent photons with MeV-range energies. We compare the nuclear interaction of such a laser pulse with the standard atom-laser interaction. The mean-field description of atoms must be replaced by a rate equation and the classical field strength, far too faint in nuclei, by the dipole transition rate. Significant nuclear excitation occurs for photon numbers much smaller than typical for atoms. That drastically reduces the requirements on the experimental realization of a "flying mirror". 
Adriana P\'alffy, Paul-Gerhard Reinhard, Hans A. Weidenm\"uller
nucl-th physics.atom-ph