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Researchers show how to increase X-ray laser brightness and power using a crystal cavity and diamond mirrors

Researchers show how to increase X-ray laser brightness and power using a crystal cavity and diamond mirrors

Posted Date: 2023-08-03
Researchers show how to increase X-ray laser brightness and power using a crystal cavity and diamond mirrors
This can be a graphic illustration of a cavity-based X-ray free-electron laser. The electron beam (blue) travels by way of an undulator (brown and white). Contained in the undulator, the beam releases X-ray pulses (orange). These pulses bounce round a set of 4 mirrors till they’ve reworked from incoherent to coherent X-rays (yellow). The coherent X-rays then depart the cavity mirror system utilizing the researcher staff’s Q-switching approach and proceed down the accelerator to scientists inside experimental halls. Credit score: Greg Stewart/SLAC Nationwide Accelerator Laboratory

At particle accelerator amenities around the globe, scientists depend on highly effective X-rays to disclose the construction and habits of atoms and molecules. Now, researchers from the Division of Vitality’s SLAC Nationwide Accelerator Laboratory have calculated how you can make X-ray pulses at X-ray free-electron lasers (XFEL) even brighter and extra dependable by constructing a particular cavity chamber and diamond mirrors round an XFEL.

“We wish to make our XFELs extra laser-like,” mentioned Zhirong Huang, a SLAC and Stanford professor of photon science. “We’ve been trying to find a approach to do that for many years, and with our new calculations, we exhibit that this pipedream may grow to be actuality.”

At XFELs like SLAC’s Linac Coherent Mild Supply (LCLS), the ability of particular person X-ray pulses varies from pulse to pulse. The result's temporally incoherent gentle rays—much less laser-like lasers—that are harder for scientists to make use of to finish experiments as a result of they're much less predictable.

In a brand new research, detailed this month in Bodily Assessment Letters, researchers present how you can generate coherent X-ray pulses utilizing an intricate crystal cavity and mirror system—and while not having a cavity that's terribly lengthy and sophisticated.

“The motivation for producing coherent, increased brightness X-rays is to review real-world supplies and what occurs to these supplies below totally different circumstances,” SLAC scientist and paper co-author Jingyi Tang mentioned. “We wish to research techniques which are extra dynamic and tough to seize.”

Storing gentle utilizing mirrors

The concept of catching X-rays utilizing mirrors may appear unattainable at first thought. However at a high-repetition-rate accelerator like LCLS-II, such an concept could possibly be potential—you probably have the best storage tools and creativeness.

The researchers studied what’s referred to as a cavity-based X-ray Free electron laser (CBXFEL). On this design, a cavity construction—perhaps lots of of meters or much more than a kilometer lengthy—captures incoherent X-ray pulses which have been generated at an accelerator facility, just like the one at SLAC.

Contained in the cavity, X-rays bounce off of 4 diamond mirrors, which ship the X-ray pulses in rectangular laps. Whereas the pulses run round inside the cavity, the following electron bunch inside the accelerator travels towards them. When the bunch arrives, the bouncing X-ray pulse interacts with the electron bunch, tightening it up and organizing it. When wiggled about in a tool referred to as an undulator, this tighter electron bunch will produce extra coherent and brighter X-rays farther down the accelerator.

Previous to their new calculations, researchers thought that sustaining an X-ray pulse’s energy because it bounced across the cavity may require carefully spaced electron bunches or a kilometers lengthy cavity, making the thought a lot tougher to implement.

“We confirmed {that a} high-quality cavity system may solely have to be 100-300 meters lengthy, even with a robust XFEL working at slower repetition price, which implies more room between electrons bunches,” SLAC scientist and co-author Zhen Zhang mentioned.

Controlling the cavity loss

The important thing to this new design is controlling what researchers name the standard issue of the cavity, Q. The standard issue represents the reflectivity of the mirrors within the cavity. A excessive Q worth means very excessive reflectivity, which permits the X-ray energy to recirculate within the cavity with little loss. A decrease Q worth means decrease reflectivity, which means important quantity of X-rays depart the cavity and are transmitted down the accelerator.

When the X-rays are recirculated in a shorter cavity with none interplay with the electron bunch, Q is saved very excessive. When these X-rays work together with an incoming electron bunch, researchers can exactly management the amplified X-ray wavelength and spectrum to vary the cavity Q—referred to as Q-switching. Which means they'll decrease the Q worth when the X-rays have excessive sufficient energy—i.e., when the X-rays are prepared to depart the cavity and journey down the accelerator to experiments.

By controlling Q, researchers may give the coherent X-ray pulse their flip to recirculate a number of instances across the cavity and mirror system. This skill for the coherent X-ray pulses to now journey across the system with little loss provides the pulses extra time to construct up energy, thus shortening the wanted cavity size and creating X-rays with excessive output energy.

Within the coming yr, scientists and engineers at SLAC, in collaboration with Argonne Nationwide Laboratory and different establishments, are engaged on constructing a take a look at cavity at SLAC’s LCLS. The preliminary objectives of the experiment are to exhibit the ability improve after the X-ray is recirculated by the cavity and to look at the cavity’s efficiency. Q-switching is also examined on such a CBXFEL system after the preliminary objectives of the experiment are reached, researchers mentioned.

Offered by SLAC Nationwide Accelerator Laboratory