X-ray Free Electron Laser (XFEL) is an X-ray combining the features of lasers at the free electron state. It may be the most promising light source for the next generation of scientific exploration and discovery.

X-rays are well known from their uses in medicine, but they are also widely used in advanced science. When observing objects, nothing smaller than the wavelength of the light can be seen. To observe smaller objects, a shorter wavelength needs to be used. Using X-rays even the individual atoms of an object can be seen. SPring-8, in Hyogo prefecture, can produce the brightest light in the world over a wide range of wavelengths including X-rays, and is being used in life science and materials science research.

The X-rays produced at SPring-8 are ten billion times brighter than the sun. However, the peaks and troughs of the light waves are not aligned. Laser light is light with its waves aligned. The light produced by the XFEL will be a billion times brighter than SPring-8. A brighter light will be a major step forward and enable us to observe faster movement in a smaller region.

In Japan, the SPring-8 Joint Project between RIKEN and JASRI has been developing the XFEL with the aim of completing it in fiscal 2010. The prototype accelerator which succeeded in creating a laser beam this time has basically the same structure as the XFEL itself will, and was designed for use in demonstration experiments that can check the component technologies needed for the actual XFEL.