A one-dimensional theory is given for the suppression of the sideband instability in tapered free-electron laser amplifiers operating in the Compton regime. It is demonstrated that strong tapering can reduce drastically the intensity of sideband radiation. It is shown that the frequency of the most unstable sideband mode varies continuously along the wiggler axis while the peak growth rate itself decreases. Due to this continuous detuning effect, no single sideband mode can grow at a fixed maximum rate along the wiggler, and hence, only a suppressed but broadened sideband spectrum can be formed. In a particular numerical example, we obtain an efficiency of approximately 70% with sideband intensities suppressed by eight orders of magnitude with respect to the intensity of the main signal. The theory is also applied to an inverse free-electron laser in which sidebands are eliminated.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics