The FHI free-electron laser (FEL) facility
A brief presentation
How it works?
The free-electron laser (FEL) at the Fritz Haber Institute (FHI) generates intense pulses of infrared (IR) radiation of widely tunable wavelength from 3 µm to 60 µm. Unlike conventional lasers, where the radiation is produced in a gas, liquid, or solid, in an FEL it is generated by an electron beam propagating freely through a vacuum tube. In a device called an undulator, strong magnetic fields of alternating polarity force the electrons to undergo a wiggling (undulating) motion, thereby causing the emission of radiation. The radiation wavelength can be tuned simply by varying the electron energy or the magnetic field strength. Before entering the undulator, however, the electrons must be accelerated to almost the speed of light, requiring a complex electron accelerator.
What we can do with a FEL?
The generation of molecular vibrational spectra is one of the main uses of the FHI FEL. The IR 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 to their geometrical structure.