Accelerated Physics: Test will reveal new options for synchrotron light sources

The latest light sources for research are based on material accelerators. These are large facilities in which electrons are accelerated to almost the speed of light, and then emit light pulses of a particular character. In storage ring-based synchrotron radiation sources, the electronic bases travel in the ring for billions of motions, and then generate a rapid continuity of very bright light pulses in the blown magnets. In contrast, the electron sources in free-electron lasers (FELs) are linearly accelerated and then emit a single super-bright flash of laser-like light. Storage ring stores as well as FEL sources have helped advancements in many areas in recent years, from in-depth insights into biological and medical issues to materials research, technology development, and quantum physics.

Now a Sino-German team has shown that a pattern of pulses can be created in a synchrotron radiation source that combines the benefits of both systems. The synchrotron source delivers short, intense microbes of electrons that deliver radiation pulses that have a laser-like character (as with FELn), but that can follow each other closely in sequence (such as which has synchrotron light sources).

The idea was developed about a decade ago under the “Steady-State Microbunching” (SSMB) catchphrase under the guidance of acceleration theorist Alexander Chao and his PhD student Daniel Ratner at Stanford University. The equipment should also enable storage rings to generate light pulses not only at a high repetition rate, but also as intelligent radiation as a laser. The young physicist Xiujie Deng from Tsinghua University, Beijing, built these ideas into his doctoral work and studied them more theoretically. Chao established contact with the accelerators at HZB in 2017 that will operate PTB’s Light Metrology (MLS) Source as well as HZB’s BESSY II soft X-ray source. The MLS is the world’s first light source augmented by a design for operation in the so-called “low alpha mode”. The electron bases can be significantly shortened in this mode. The researchers there have been developing this particular approach consistently for over 10 years. “As a result of this development work, we were now able to meet the challenging corporate requirements for validating the SSMB principle at the MLS,” explained Markus Ries, acceleration expert at HZB.

“The theory group within the SSMB team had defined the physical boundary conditions for optimal device performance during the preparation phase. This allowed us to generate the novel device states with the MLS and modified them enough with Deng to be able to find the pulse patterns we were looking for “, reports Jörg Feikes, an acceleration physics expert at HZB. The HZB and PTB experts used an optical laser whose light wave was connected in spatial and temporal synchronization with the electron sources in the MLS. This altered the electrical energy in the sources. “This causes the electronic bases, which are a few millimeters long, to enter microbunches (just 1 μm long) after just one turn in the storage ring, and then emitting light pulses that increase each other correspondingly as in a laser “, explains Jörg Feikes.” The empirical detection of the sensible radiation was anything but easy, but improved our PTB colleagues pioneered an innovative optical detection unit with which the discovery was successful. ”

“The main sources of future SSMBs are that they also generate laser-like radiation beyond the visible spectrum of‘ light ’, in the EUV range, for example,” says Dr. Mathias Richter, head of department at PTB. And Ries confirms: “In the final stage, an SSMB source could deliver radiation of a new character. The beats are intense, focused and narrow band. They combine the benefits of synchrotron light with the benefits of FEL beats. , Feikes said: “This radiation may be suitable for industrial applications. The first SSMB – based light source is specifically for application in EUV lithography already at the design stage. near Beijing. ”

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The work was published on February 24, 2021 in the major scientific publication Nature.