Collective free-electron laser studies

We present the results of a series of collective free-electron laser (FEL) experiments. Under the conditions of a resonant pump, a wide-band emission spectrum (50-350 GHz) is observed. However, in nonresonant conditions, very little radiation is detected from the laser. Occurrence of the emission for a resonant pump is explained using a very simple model. The wide-band nature of the emitted radiation is not completely understood.