Tabletop X-ray device rivals world's largest machines

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The image shows an x-ray radiograph of a resolution test target, with features as small as 3 micrometer. It demonstrates that the x-rays produced with a table-top laser plasma interaction have a source size of around one micrometer and a peak brightness comparable to 3rd generation synchrotrons. The image was taken in a single shot exposure of 30 femtoseconds.

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Researchers from Imperial College London, the University of Michigan and Instituto Superior Téchnico Lisbon have created a tabletop device that produces synchrotron X-rays, the energy and image quality of which are as good as some of the largest, most expensive X-ray facilities on the planet. It uses a high power laser combined with a tiny jet of helium gas to produce an ultrashort high energy beam, that could be used for everything from examining molecules to checking the integrity of airplane wings.

The new device’s X-rays have an extremely short pulse length, and originate from a point only about one micron in width. This results in an unusually narrow beam, which allows users to see finer details than other technologies permit. Because the pulses are so short, users could even measure atomic and molecular interactions that occur on a femtosecond (one quadrillionth of a second) timescale.

The team started with an experiment at the University of Michigan, in which they shone a very high power laser beam into a jet of helium gas. This created a tiny column of ionised helium plasma. Within that column, the laser pulse created a bubble of positively charged helium ions surrounded by a sheath of negatively charged electrons. Because of the separation of positive and negative charges, the bubble contained powerful electrical fields that accelerated some of the plasma’s electrons to form an energetic beam, while also causing that beam to wiggle. That wiggling produced a “highly collimated co-propagating X-ray beam,� which is at the heart of the device.

It is a process similar to that which happens in conventional synchrotron machines, but on a much smaller scale – the UK’s Diamond Light Source synchrotron is half a kilometer (547 yards) in circumference, while the new device is housed in a vacuum chamber that measures about one meter (3.28 feet) on each side, with the acceleration and X-ray production happening over an area of less than a centimeter.

“This is a very exciting development,� said the study’s lead author Dr. Stefan Kneip, of Imperial College. “We have taken the first steps to making it much easier and cheaper to produce very high energy, high quality X-rays. Extraordinarily, the inherent properties of our relatively simple system generates, in a few millimeters, a high quality X-ray beam that rivals beams produced from synchrotron sources that are hundreds of meters long. Although our technique will not now directly compete with the few large X-ray sources around the world, for some applications it will enable important measurements which have not been possible until now.�

The research was published this Monday in the journal Nature Physics.

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