A tunable X-ray source hundreds of times smaller than a conventional synchrotron is reported online this week in Nature Physics (doi: 10.1038/nphys1404). The demonstration is an important step towards reducing the cost and increasing the availability of coherent, ultrafast, pulsed sources of X-rays, which are increasingly important tools in drug discovery, materials science, biology, nanotechnology and fundamental physics research.

High-intensity X-ray sources such as synchrotrons and free-electron lasers require large particle accelerators to produce bursts of electrons travelling at close to the speed of light.  The electrons are then fed into a structure known as an undulator, which causes them to emit an intense burst of coherent radiation. Owing to the size and cost of the accelerator component of these X-ray sources—typically hundreds of metres in diameter and up to $1 billion—only a few dozen devices have ever been built.

Matthias Fuchs and colleagues at the Max-Planck-Institut für Quantenoptik, Garching, Germany, replace these conventional accelerators with a so-called laser-plasma wakefield accelerator. This uses a high-intensity laser to generate a beam of high-energy electrons over a distance of just a few centimetres. Being much smaller and cheaper, laser-driven X-ray sources should be considerably easier for individual universities to build and maintain.

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