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28.09.2010
FLASH opens the view through the water window
The free-electron laser FLASH (Free-Electron Laser in Hamburg) has set a new record: this weekend, the FLASH accelerator team operated the FEL ...
The free-electron laser FLASH (Free-Electron Laser in Hamburg) has set a new record: this weekend, the FLASH accelerator team operated the FEL with an electron energy of 1.25 Giga electronvolts, thus reaching a wavelength of 4.12 nanometres. For the first time FLASH has generated laser light in the so-called water window using the fundamental wavelength – so far this was only reached with laser harmonics. The flashes with the short wavelengths had an average energy of 70 and a peak energy of 130 micro joules.
“Congratulations to the FLASH team for their outstanding work,” said accelerator director Reinhard Brinkmann. “By optimisation of the accelerator, they increased the electron energy by another 50 MeV and – reaching the water window – created brilliant conditions for FLASH scientists.”
The water window is a wavelength region between 2.3 and 4.4 nanometres. In this wavelength region, water is transparent for light, i.e. it does not absorb FEL light. This opens up the possibility to investigate samples in an aqueous solution. This plays an important role especially for biological samples, because carbon atoms in these samples are highly opaque to the X-ray radiation, while the surrounding water is transparent and therefore not disturbing.
Additional measurements with extremely short wavelengths are scheduled for November. From the beginning of April 2011, the FEL radiation will give users the opportunity to look through the water window.
