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17 Jun 2002
A free electron laser (FEL) at the DESY laboratory in Hamburg, Germany, has achieved a beam with a wavelength of just 109 nanometers.
This ultraviolet beam was produced at the DESY superconducting electron accelerator by a team of scientists from 38 institutions in 9 different countries. These scientists are working on the TESLA (TeV-Energy Superconducting Linear Accelerator) project, which aims to build a 300 meter long FEL that will give wavelengths down to 6 nanometers by the year 2003. There are currently no high-intensity lasers in the X-ray region but these wavelengths are very important for gaining insight into the structures of living cells, molecules and materials.
FELs normally produce light by firing a beam of energetic electrons in a zigzag path through a series of magnetic fields. This causes them to radiate light, which is stored inside a mirrored cavity. The photons reflect back and forth within the cavity and help to stimulate the electrons to radiate more light. This amplifies the higher-energy light beam and gives a coherent, tunable light source. However, this method cannot be employed for generating light with a wavelength of less than about 150 nanometres because the mirrors are not effective and the light cannot be accumulated. In the TESLA project the researchers removed the mirrors and instead let the radiation amplify itself in a single pass by allowing the electrons to travel through a very long zigzag path. They observed a radiation amplification that was a factor of 150 above the normal spontaneous emission. This method has already been employed for infrared and visible light, but 109 nanometers is the shortest wavelength achieved with an FEL.
Participants in the TESLA project include scientists from Armenia, China, Finland, France, Germany, Italy, Poland, Russia and the US.
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