Evolution and limits of spectral bandwidth in free electron lasers

摘要

We study the bandwidths in free electron lasers (FELs) under different circumstances; for weakly saturated FELs in storage rings, the bandwidth is given be the formula derived in the super mode theory, while it is given by the Fourier transform of the electron pulse length in the strongly saturated FELs in linacs. The limiting bandwidth for the case of a DC beam is given by a Schawlow-Townes formula, but the approach to the limit is very slow. 14 refs.