Observation of Sideband Instability in the Novosibirsk Terahertz Free Electron Laser

Sideband instability was observed very clearly in the long-pulse regime of the Novosibirsk terahertz free electron laser (FEL) by a Bruker vacuum Fourier spectrometer IFS-66v. For positive frequency detuning, simultaneous generation of six sideband modes was observed. Mode competition and mode switching have been registered. Negative frequency detuning decreased the number of sideband modes and an single-mode generation with the narrowest classical spectrum has been obtained for sufficiently large detuning .