Oscillations in superradiance with long-duration pumping pulses

We describe an experimental study of a new regime of superradiance characterized by relaxation oscillations, which is obtained in the case of long-duration pumping pulses. A qualitative interpretation of our results is given using the mean-field approximation in conjunction with broadband excitation. A more quantitative interpretation is also given, in which propagation effects are explicitely taken into account and the excitation is purely monochromatic.