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Title |
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| MOPPH016 |
Gain Deterioration at Particular Wavelengths in a Partially Waveguided FEL
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36 |
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- U. Lehnert, P. Michel, G. Staats, J. Teichert, R. Wuensch
FZD, Dresden
- V. B. Asgegar
University of Pune, Pune
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At ELBE certain wavelengths within the working range of the FIR-FEL have been found to be inaccessible. The FEL either completely stops lasing or shows marked drop-outs in the observed optical spectra. The reason of this behaviour is sought in the use of a partial waveguide through the undulator to the downstream mirror combined with free optical propagation to the upstream mirror. The light pulse from the upstream mirror couples into the lowest transverse mode of the waveguide with minor contributions of other modes. The light generated in the gain process, however, is distributed over some of these modes and experiences dispersion over the waveguided propagation length. At the exit of the waveguide the different modes recombine with certain phase shifts. Depending on the amount of phase shift and the mode composition of the light a gain drop or even inversion is possible if a major part of the stimulated emission is out of phase to the primary beam. This work attempts to compute the mode distribution of the stimulated light emission and to translate this into a prediction of those wavelengths where the gain is markedly reduced by destructive interference of different modes.
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