Q&A: Researchers Explain a Strange High-Intensity Result during SLAC’s X-ray Laser

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At intensely high intensities, X-rays stop working like a ones in your doctor’s bureau and start interacting with matter in really opposite ways. This “nonlinear” X-ray function can customarily be seen during X-ray free-electron lasers.

The Linac Coherent Light Source X-ray laser during SLAC (SLAC National Accelerator Laboratory)

The Linac Coherent Light Source X-ray laser during SLAC (SLAC National Accelerator Laboratory)

Recent experiments during a Department of Energy’s SLAC National Accelerator Laboratory have suggested a new, astonishing turn in that function that might be one for a textbooks and could change a approach these absolute lasers examine matter. Here a leaders of a initial team, David Reis of Stanford PULSE Institute and Matthias Fuchs of a University of Nebraska-Lincoln, report a results, reported final week in Nature Physics.

What was your examination about?

In this examination we investigated one of a many elemental interactions between X-rays and matter – a routine where dual X-ray photons, or particles of light, strike an atom during a same time. In a routine a dual photons are converted into a singular higher-energy X-ray photon. Under normal resources such a acclimatisation does not happen, though we know from experiments regulating manifest light that it can start during intensely high light intensities.

This “nonlinear” function was detected during visual wavelengths in a 1960s regulating a device that was new and insubordinate behind then: a laser. Now it is being exploited in roughly each laboratory that uses lasers, and even some straightforwardly accessible laser pointers are formed on this technology. But until recently it could not be celebrated during X-ray wavelengths given they could not be constructed during high adequate intensities. Therefore, we had to use a totally new source of X-rays, a supposed X-ray free-electron laser or XFEL.

How are XFELs different?

XFELs are zero like a standard laser; they are huge machines some-more than half a mile long. They have customarily recently turn operational after decades of growth and customarily dual exist worldwide – a Linac Coherent Light Source (LCLS) during SLAC and SACLA in Japan. These XFELs beget deviation with rare properties. For a examination we took advantage of a fact that that they can furnish intensely heated X-rays, some-more than a trillion times brighter than a sun.

Experiments during XFELs customarily need a extended operation of expertise. Our initial group enclosed researchers from SLAC, Stanford University, Bar-Ilan University in Israel and a University of Nebraska, Lincoln.

Tell us how a examination worked.

During a examination we generated an intensely heated X-ray lamp by focusing a full outlay from a LCLS into a mark only 100 nanometers, or billionths of a meter, wide. That’s like focusing all a solar deviation that hits a Earth’s aspect into a mark a hole of a tellurian hair. To a believe this was a highest-intensity X-ray lamp that had ever been used in an experiment. We destined that splendid mark onto a tiny square of beryllium metal, and collect a higher-energy photons that came out on a special pixelated X-ray detector.

We indispensable such impassioned intensities to urge a possibility that dual photons would accommodate adult during accurately a right place and time on one of a many atoms bright by a beam, and so trigger a nonlinear interaction. Even so, a luck that this will start on any given atom is reduction than a contingency of winning a lottery.

The examination was a really initial review of this kind, so we were entering uncharted territory. But we were means to use speculation and extrapolations from prior experiments to envision what we approaching to see.

And is that what we saw?

No! What we design to see when dual X-ray photons strike a beryllium atom is that a appetite of a dual photons going in is equal to a appetite of whatever comes behind out. In this box a appetite that comes out is common between a singular higher-energy photon that’s issued and an nucleus that’s ejected from a atom.

But in a experiment, a appetite of a higher-energy X-ray photons entrance out of a communication was many reduce than expected, implying a many aloft appetite electron. This shows that a production of a communication seems to be many richer and even many some-more engaging than primarily anticipated.

When we initial due this experiment, a lot of people asked because we wanted to do it, given a approaching formula were already known. The fact that a measurements do not determine with a primarily approaching formula shows a extensive value of simple science. It is intensely sparkling to work on investigations of such elemental processes. As one unknown counterpart reviewer wrote: “Ultimately, as this becomes improved understood, it will seem in all textbooks on X-ray production and nonlinear optics.”

What’s next?

This examination is only a beginning. We will shortly perform even some-more worldly experiments with improved orchestration to improved know this newly detected phenomenon. If they endorse a new bargain of this elemental process, it might have a poignant impact on destiny experiments achieved with high-intensity X-rays – including many XFEL experiments. It could also lead to novel ways of probing matter.

How so?

It has been shown that when X-rays separate off a electrons in a solid, those electrons can act roughly as if they were giveaway from a atoms that connect them, so we can’t tell what form of atom a given nucleus belongs to. However, in a nonlinear interactions we observed, a electrons behaved as if they were some-more firmly firm to their primogenitor atoms. If a resource we consider is obliged for this is correct, it gives we a whole new approach to investigate materials with XFELs. The X-rays could tell we what kinds of atoms are in a element – what a chemical combination is – and during a same time tell we how a atoms are arranged. For a initial time we would be means to get both forms of information from a singular experiment.

Citation: M. Fuchs et al, Nature Physics, 31 Aug 2015 (10.1038/nphys3452)

Source: SLAC