Fritz-Haber-Institut der Max-Planck-Gesellschaft




User experiments


The FHI free electron laser (FEL) project


In 2010, the construction of the FHI free electron laser started. First light is expected for fall 2011. The FEL will provide intense and tunable pulsed radiation throughout the infrared region, opening up new possibilities for the ongoing research at the FHI with a main application being vibrational spectroscopy of molecules. The light output of the FEL will be tunable from 4 µm to 40 µm, at a later stage up to 400 µm. This spectral region is often referred to as the `molecular fingerprint' region, as it is the region in which the fundamental vibrational modes of molecules, clusters or solid materials are located. These vibrational modes are directly connected to the forces that hold the atoms together, and are thereby a direct probe of the geometrical arrangement of the atoms.

The implementation

Ever since the first demonstration of a free electron laser in 1976 at Stanford University, it was realized that this type of laser can potentially deliver high-power radiation over a large spectral range. A layout of the FHI-FEL is shown in the figure:

Electrons are emitted from the electron gun. After acceleration to an energy of up to 50 MeV (mega-electronvolt) by two linear accelerators (LINACs), the electron beam is bend and injected into the resonator, consisting of two high-reflectivity mirrors at each end of the undulator. The magnetic field in the undulator is perpendicular to the direction of the electron beam and periodically changes polarity a (large) number of times along its length. This causes a periodic deflection, a `wiggling' motion, of the electrons while traversing the undulator. This wiggling causes the emission of light and its wavelength is determined by the electron energy as well as the undulator parameters. The initial weak radiation is captured in the resonator and amplified by interaction with successive electron bunches. A small hole in one of the two resonator mirrors couples out some light, which is send to user experiments.

The following research groups and companies have contributed:

EditUploadEditSideBar © FHI