Theoretical investigation of a waveguide application in a FEL with large μc

Abstract

A free electron laser with a planar undulator, operating with a train of short electron pulses (3–6 ps) in the far infrared region (λ = 100–300 μm) was studied. The parameter μc defined as the ratio of the slippage length to the electron pulse length, can be rather large even for λ = 100 μm (μc ≈ 10). An increase in the radiation wavelength λ leads to an increase in both μc and diffraction losses.The introduction of a waveguide into the optical cavity provides an opportunity to decrease the diffraction losses. To analyze such systems a new code including pulse propagation through a waveguide was used. It was shown that the waveguide dispersion leads to a considerable variation of the pulse shape and an additional shift of the radiation pulse which can be comparable to the slippage length. This effect changes the optimal values of the cavity detuning and can even reduce the output power.Configurations with both circular and rectangular waveguides were analyzed. Results were compared with corresponding results without waveguides.