FZD, Dresden
Two free-electron lasers (FELBE; 4-21 μm and 18-250 μm, respectively) have been in routine user operation for a wide range of IR experiments at the radiation source ELBE in the Forschungszentrum Dresden-Rossendorf for several years. The lasers are driven by a superconducting RF linac that permits the generation of a cw-beam with a repetition rate of 13 MHz and a high average beam power. In addition, operation in a macropulse modus (pulse duration >100 μs, repetition rate ≤ 25 Hz) is possible. A few important experiments using the cw-operation are discussed. Furthermore, an outlook is given on the experiments which use the beam of FELBE in the High Magnetic Field Laboratory Dresden (HLD). The HLD provides pulsed magnetic fields up to 60 T. It operates as a user facility since 2007.
LBNL, Berkeley, California
UCB, Berkeley, California
ANL, Argonne
A concept for a tunable soft x-ray free electron laser (FEL) oscillator is proposed and studied numerically. It is based on the idea of echo enabled harmonic generation [1] and takes advantage of the oscillator’s ability to start up from spontaneous emission, thereby eliminating the need for optical lasers. In the proposed concept, harmonic tunability is accomplished through beam manipulations using magnetic chicanes and a tunable radiator while two FEL oscillators remain at a fixed frequency. An additional advantage of the proposed technique is the possibility to utilize multilayer x-ray mirrors with a high backward reflectivity of the order of 70%, allowing the initial beam manipulation to be accomplished at a short wavelength, close to the final soft x-ray output. The high repetition rate soft x-ray output is expected to have longitudinal coherence and a narrow bandwidth.
[1] G. Stupakov, PRL, 2009
JLAB, Newport News, Virginia
ATF, Boulder
Mesa+, Enschede
We report on the design, and broadly tunable operation, of a high average power free-electron laser using edge-outcoupling. For this type of outcoupling, the cavity mode has a larger area than the mirror diameter, and the mode ‘spills” around it. While used in positive branch unstable resonators, in this case, the resonator was in a stable configuration. Using an edge-outcoupler composed of an aluminum-coated sapphire substrate, the IR Upgrade FEL at Jefferson Lab achieved a maximum power of 260W at 3.87 microns, with an output power of 20 W or higher from 0.8 to 4.2 microns. Measurements of gain, loss, and output mode are compared with our models.
FOM Rijnhuizen, Nieuwegein
Several of the short-pulse FELs that are operated in a wavelength range starting well below and ending well above 100 microns make use of a partial waveguide in the resonator and a central hole in one of the mirrors for outcoupling. The purpose of the waveguide is to confine the optical mode, in particular within the gap of the undulator. Experimentally, it was found that these FELs suffer from one or a number of tuning 'gaps': narrow wavelength windows within the tuning range where the output is strongly reduced or where the laser even does not turn on. Recently, Prazeres et al.[1] , using a simulation model, were able to reproduce some of the main features of the tuning curve and showed that the cavity outcoupling and losses change abruptly across a tuning gap. In this contribution we will present experimental results for the gain, cavity loss, saturated power and spectral intensity across one of the most prominent gaps in the tuning curve of the FELIX long-wavelength FEL. Both for the normal case and for the case where a slit is used to limit the optical mode extent on the free-space mirror.
[1]. R. Prazeres, F. Glotin, and J.-M. Ortega, PRST-AB, 12 (2009) 010701