The primary application of the facility is in the studies of the vibrational dynamics of molecules, liquids, and solids, but other applications requiring an intense source in the spectral range covered, such as photo-ablation of tissue, near-field microscopy or linear spectroscopy of small-sized samples, are equally appropiate. Users can be grouped into three categories:

• In-house user group Molecular dynamics
• UK research programme
• External users

Research areas

• Molecular Physics and Chemistry
• Solid-state and Semiconductor Physics
• FEL Physics and Laser Physics
• Miscellaneous

Molecular Physics and Chemistry

Most of the research in the field of molecular physics and chemistry at FELIX is carried out by the in-house user group 'Molecular Dynamics'. Their main research topics are:

• Metal cluster dynamics
• Infrared absorption spectroscopy of jet-cooled biomolecules
• Infrared spectroscopy of Poly Aromatic Hydrocarbon ions and other "exotic" gas phase ions
• Infrared spectrocopy and dissociation dymanics of unstable species

More detailed information can be obtained from the Molecular dynamics website

Solid State Physics

The main activities in this field are carried out under the contract between the facility and the British research council EPSRC. The main topics of the UK research programme are

• Inter- and Intraband relaxation in quantum confined semiconductor structures and lifetime engineering in narrow-gap semiconductors
• Dynamics of spatially localised vibrations in ionic crystals
• Electron cyclotron resonance spectroscopy using pulsed magnetic fields upto 45 T

FEL Physics and Laser Physics

The main objective of the quantum electronics program was to produce ultra-short optical pulses of high intensity with FELIX. Therefore, it was necessary to understand the saturation process in an FEL operating in the large-slippage regime. For a long time FELIX was one of the very few FELs that operated in the regime of strong slippage, where the ratio between the number of undulator periods times the wavelength and the length of the electron bunch is considerably larger than 1. Therefore, many of the observations associated with this regime (limit-cycles, efficiency enhancement, coherent start-up, short pulses, etc.), were first made in FELIX.

At the same time, diagnostics had to be developed in order to be able to characterise these pulses as well as the electron beam that drives the laser. Presently no proven technique exists that allows an accurate measurement of the electron bunches having a duration of less than a picosecond, as is the case for the ultra-bright linear accelerators being built today. Electro-optic sampling is considered by many as one of the most promesing techniques proposed. Since a few years, several groups are therefore actively pursuing the use of electro-optic sampling to measure the electric field of electron bunches. Our demonstration of sub-ps time resolution and recently the single-shot capability is therefore very encouraging (more).

Miscellaneous

A good impression of the other research areas can be obtained from the list of publications and highlights.