The setup of the Free-Electron Laser at ELBE
The FELs of ELBE are Compton FELs with an optical resonator working in the upper region of the low-gain regime (G ≈ 10 - 80%). The main components of a FELBE FEL are the undulator and the optical resonator (see the figure on the right side).
The electron beam from the accelerator is deflected by a dipole bending magnet and enters the undulator along its symmetry axis. The undulator consists of a set of alternating magnets causing the electron beam to wiggle perpendicular to the magnetic field. The wiggling electrons produce light within a narrow conus around the undulator axis with a definite wavelength (spontanious emission). Behind the undulator the electrons are deflected by another bending magnet into a beam dump. The light is confined in an optical resonator consisting of two focussing mirrors on both sides of the undulator axis. The electron and the produced light beam consist of extremly short pulses (≈1 mm long). The resonator length (distance between the two mirrors is determined such that a cycling light pulse hits the subsequent electron pulse at the entrance of the undulator. Passing the undulator with nearly the same velocity the electron beam transfers energy to the electromagnetic field of the light pulse. The relative increase of field energy per pass is described by the single-pass gain. If the field is weak the gain is constant (small-signal gain). Increasing the field in the resonator the gain decreases (saturation) until a value is reached just compensating the radiation losses in the resonator including the fraction outcoupled by a hole in the upstream mirror. The outcoupled beam is delivered to the laboratories where it is used for various kinds of experiments.
Here you can find details about about the components of the FELs and their parameters such as
- the undulators U27 and U100,
- their wavelength range,
- the expected single-pass gain,
- the setup of the optical resonators including a partial waveguide, and
- a model of the power buildup, and
- the expected laser power produced by the ELBE undulators.
Additionally you can inform yourself of the electron beam line and diagnostics.