The free electron laser has almost the same properties as the optical type, meaning the coherent beam of electron radiation, but uses different operating principles to create the beam. Unlike gas, liquid, or solid-state laser applications, such as diode lasers, which rely on bound atomic or
molecular states, Free electron lasers use a relativistic electron beam as the lasing medium, hence the term free electron.
The first free electron laser that will produce x-rays is nearly completed and has been built by the Argonne Laboratories. It represents a milestone in the completion of an ambitious project, Linac Coherent Light Source (LCLS) undulator system.
This undulator, once completed, will be capable of producing hard-rays and will be presented at the Stanford Linear Accelerator Center (SLAC) in 2009. It is based on a combination of brightness from laser sources and penetration power along with atomic sensitivity of the X-rays.
When finished, the undulator system will be 130-meter long and will include magnets, vacuum systems, support structures, beam diagnostics and controls, to produce a precise magnetic field with an electron beam traveling through it.
Forcing the electrons to oscillate back and forth, the magnetic fields produced by the undulators will thus create large amounts of x-rays, that interact again with the electron to make them bunch at x-ray wavelengths.
When this happens, the electrons will emit a coherent beam of light that will cause a large gain in radiation power that raises the X-rays' intensity.
"Argonne was tapped to participate in this project due to the expertise demonstrated with the Advanced Photon Source undulator systems," said J. Murray Gibson, associate laboratory director of Argonne's Scientific User Facilities. "An X-ray laser such as LCLS will open up new scientific frontiers and represents an immense technical achievement for the United States. We could not have done this without the partnership of national laboratories, universities and industry."