First lasing of the Darmstadt cw free electron laser

3 GHz digital rf control at the superconducting Darmstadt electron linear accelerator: First results from the baseband approach and extensions for other frequencies

“…The analysis and the control of the baseband signals is done by a low frequency module, which was built with analogue components. These control loops performed quite well, leading to a high quality beam, which for example was essential for the success of the free electron laser operation in the 1990's [7]. Nevertheless, the maintenance effort of the existing system has become more difficult in time because of the aging of all components.…”

“…The design quality factor Q is 3 Â 10 9 at an accelerating gradient of 5 MV=m. Even when the sc cavities are strongly coupled with a loaded quality factor of 3 Â 10 7 , which leads to a resonance width of some 100 Hz, they are very sensitive against microphonic perturbations [2]. In order to achieve the recommended energy spread of AE1 Â 10 À4 at the experimental areas, the amplitude and phase of the cavities have to be controlled strictly to compensate the impact of microphonic perturbations.…”

THz radiation from free electron lasers and its potential for cell and tissue studies

“…Thus selective modifications of tissue-surfaces become possible; they require high laser power and eventually the pulse time structure has to be properly adjusted (Olmes et al 1997). Both may be obtained from a FEL but not easily from other sources (Brunken et al 1999, Awazu et al 2001, Junbiao et al 2001. (b) The FEL pulse length is in the picosecond (ps) range allowing interesting investigation of dynamical processes by pump-probe techniques.…”