Step-tapered operation of the FEL: Efficiency enhancement and two-colour operation
- Commissariat a l`Energie Atomique, Bruycres-le-Chatel (France)
- Centre Universitaire Paris-Sud, Orsay (France); and others
We present new measurements of the temporal and spectral properties of radiation produced from two step-tapered undulator free-electron lasers (FEL), CLIO in France and FELIX in the Netherlands. Using a two section undulator with independently adjustable deflection parameters (K) the FEL will operate either with enhanced efficiency and improved spectral properties (with a small positive {Delta}K step) or will operate simultaneously at two frequencies (for large {Delta}K). The first experiments demonstrating at two-colour operation were restricted to a maximum wavelength difference, {delta}{lambda}/{lambda} < 0.15 because of the influence of optical dispersion in the cavity introduced by a dielectric output coupling plate. Using a dispersion-free hole output coupler the maximum {delta}{lambda}/{lambda} has been extended to more than 0.6. We present these new dispersion-less two-colour operation results and show that quenching of one of the wavelength unless the optical cavity is detuned significantly so that the FEL operates with reduced efficiency and lower intracavity power. To overcome this problem a larger fraction of the radiation will need to be coupled in the future to limit the intracavity power. To determine the temporal distribution of the optical radiation at the two wavelengths we have carried out second order autocorrelation measurements using a nonlinear crystal and established that the optical pulses are very short, a few hundreds of femtoseconds long, and overlapping. To establish how the two colours build up in the cavity we have also measured the spectral and temporal evolution of the macropulse. To establish the efficiency over a wide range of {Delta}K values we have measured the electron spectra of the electrons leaving the undulator and find that the efficiency is enhanced significantly over normal undulator operation.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- OSTI ID:
- 238865
- Report Number(s):
- BNL-61982-Absts.; CONF-9508156-Absts.; ON: DE96002729; TRN: 96:013355
- Resource Relation:
- Journal Volume: 375; Journal Issue: 1-3; Conference: 17. international free electron laser conference, New York, NY (United States), 21-25 Aug 1995; Other Information: PBD: [1995]; Related Information: Is Part Of 17th international free electron laser conference and 2nd international FEL users` workshop. Program and abstracts; PB: 300 p.
- Country of Publication:
- United States
- Language:
- English
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