Wuensch, R.

Paper	Title	Page
MOPPH016	Gain Deterioration at Particular Wavelengths in a Partially Waveguided FEL	36
	U. Lehnert, P. Michel, G. Staats, J. Teichert, R. Wuensch FZD, Dresden V. B. Asgegar University of Pune, Pune
	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.
TUAAU05	Design of the Nijmegen High-Resolution THz-FEL	200
	R. T. Jongma Radboud University Nijmegen, Institute of Molecules and Materials, Nijmegen K. Dunkel, C. Piel ACCEL, Bergisch Gladbach U. Lehnert, P. Michel, R. Wuensch FZD, Dresden C. A.J. van der Geer Pulsar Physics, Eindhoven A. F.G. van der Meer FOM Rijnhuizen, Nieuwegein P. J.M. van der Slot Twente University, Laser Physics and Non-Linear Optics Group, Enschede W. J. van der Zande Institute for Molecules and Materials, Radboud University Nijmegen, Nijmegen
	In 2006, the Radboud University in Nijmegen received funding via the Netherlands NWO-BIG program to realize a THz laser system and a 45 T hybrid magnet system. The specifications of the THz FEL system are geared towards material science at high (30-45 T) magnetic fields (saturation spectroscopy and pulse-echo experiments), and applications e.g. in the field of biomolecular spectroscopy. A study performed during the last year demonstrated the feasibility of a THz FEL that will cover the 100-1500 micron spectral range and that operates in either a “spectroscopic mode” providing 100 Watt bandwidth limited pulses of several microsecond (spectral resolution better than 100000/1) or pump-probe pulsed mode providing macropulses with 3 GHz. micropulses. Technical challenges are in the 3 GHz operation of the source, and the narrowband operation. The latter will be obtained by filtering a single mode out of the frequency comb, realized by ensuring full coherence between the micropulses. Coherence is imposed by the stability of the electron beamμpulses (“spontaneous” coherence) or by the use of an intra-cavity (Fox-Smith) interferometer. We will present details of the chosen design.
	Slides