Effect of electron beam temperature on the gain of a collective free-electron laser

At sufficiently low beam currents, electron beam temperature effects cause the gains of collective (Raman) regime free-electron lasers to be lower than the predictions of cold beam theory. This gain degradation has been measured as a function of the beam current, the wiggler magnetic field, and the interaction frequency. The measurements are used to estimate the electron beam temperature, and the estimated temperature is close to the temperature predicted by numeric simulations.