Since 2005, FLASH, the world's first X-ray free-electron laser, has been generating a very special light at DESY in Hamburg: extremely intense, ultra-short pulsed X-ray laser flashes. Researchers from all over the world use it to track the movements of atoms and molecules.
FLASH accelerates electrons almost to the speed of light. Special magnetic arrangements, the "undulators", then force the electrons onto a slalom course. In the curves, the fast particles emit flashes of X-ray light that overlap and oscillate in unison. In this way, FLASH generates unimaginably intense, ultra-short flashes of light in the range of femtoseconds - i.e. quadrillionths of a second. This makes it possible to film chemical reactions, for example, which also take place at femtosecond speed. FLASH is the pioneering facility where important foundations for films from the nanocosmos were researched.
Filming chemical reactions
In order to observe the details of a chemical reaction, the researchers take countless individual images that capture all stages of the reaction. Strung together, they form a "movie" that shows the molecular events. With X-ray lasers such as FLASH, scientists can follow what really happens at the atomic and molecular level and use this knowledge to develop new materials and medicines.
DESY is the main shareholder and works closely with European XFEL to operate the facility. Together with international partners, DESY has built the heart of the X-ray laser facility - the 1.7-kilometer-long superconducting accelerator with the electron source, which DESY now also operates. The accelerator is based on the superconducting TESLA technology developed by DESY and its partners as part of the TESLA Technology Collaboration. With the FLASH free-electron laser, DESY has been operating a 300-meter-long prototype of the European XFEL since 2005, which is based on the same technology.
TESLA accelerator technology
A special feature of FLASH is the use of superconducting accelerator technology to bring the electrons to high energies. This groundbreaking technology was developed by DESY together with 50 institutes from twelve countries as part of the international TESLA Technology Collaboration. Unlike conventional systems, the TESLA accelerator elements are superconducting: In the resonators, which are cooled to minus 271 degrees Celsius, the current flows without loss, so that practically all of the electrical power fed in can be transferred to the particles - an extremely efficient method of acceleration. In addition, the superconducting resonators deliver a very fine and uniform electron beam of extremely high quality. Such a special particle beam is the prerequisite for being able to operate a free-electron laser in the X-ray range at all.
Principle of free-electron lasers
The special X-ray laser light is generated in a free-electron laser according to an ingenious principle: when slaloming through a periodic magnet arrangement (undulator), the electron bunches emit light (photons) of a fixed wavelength. The photon beam propagates in a straight line and overlaps with the electron packet. It imprints its regular structure on the electrons, i.e. after some time, the initially uniform charge density distribution has become a series of individual charge disks, each separated by one wavelength of light. Now all the electron disks radiate in unison - the light can intensify into intense laser radiation.
Expansion for the future
The international research community's interest in FLASH is enormous. For this reason, FLASH was expanded and a second tunnel section including an experimental hall with space for six measuring stations was added. This more than doubled the user capacity of FLASH and met the great demand. The two beamlines can be operated in parallel with largely independently adjustable wavelengths.
Since 2020, the wavelength of the X-ray laser light has been further shortened as part of the FLASH2020+ project and the beam quality and experimental conditions have been further optimized in order to secure the facility's leading position as an X-ray laser pioneer and trailblazer for innovative technologies in the future.
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© DESY, Marta Mayer
Dr. Thomas Zoufal
Press spokesman
© DESY, Marta Mayer
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© DESY, Marta Mayer
Heidrun Hillen
Consultant for large-scale research equipment
© DESY, Marta Mayer