When ultrafast electrons are deflected, they emit light known as synchrotron radiation. This radiation is commonly used in storage rings where magnets force particles onto a closed path. While this light typically consists of a broad spectrum of wavelengths, it is longitudinally incoherent. Monochromators can be employed to isolate specific wavelengths from the spectrum, but this significantly reduces the radiant power to only a few watts. Imagine if storage rings could deliver monochromatic, coherent light with outputs reaching several kilowatts, much like high-power lasers. Physicist Alexander Chao and his doctoral student Daniel Ratner addressed this challenge in 2010 by shortening the electron bunches orbiting in the storage ring to lengths smaller than the wavelength of the emitted light. This transformation results in coherent radiation that is millions of times more powerful.
The Role of Micro-Bunching
Chinese physicist Xiujie Deng established a set of parameters for isochrone or “low-alpha” rings in the Steady-State Micro-Bunching project. This project focuses on creating short particle bunches after interaction with a laser, with lengths as small as one micrometer. A collaborative research effort involving HZB, Tsinghua University, and PTB successfully demonstrated the viability of this concept in a proof-of-principle experiment conducted in 2021. By utilizing the Metrology Light Source (MLS) in Adlershof, the team was able to confirm Deng’s theory for generating micro-bunches through extensive experimentation. This breakthrough represents a significant advancement towards the development of a new type of SSMB radiation source, as noted by project manager Jörg Feikes from HZB. Despite the promising results, Feikes acknowledges that the realization of this technology will require substantial time and resources, drawing comparisons to the evolution of free-electron lasers which underwent decades of development before reaching their current state.
The Path Ahead for Materials Research
The ability to harness coherent light with high power outputs holds remarkable potential for materials research. By optimizing the electron bunches in storage rings to emit coherent radiation, scientists can revolutionize various applications in the field. The transition from incoherent to coherent light sources opens up new possibilities for studying materials at the atomic and molecular level with unprecedented precision and efficiency. As researchers continue to refine and expand upon the principles of micro-bunching and coherent radiation, the future of materials science is poised for exciting advancements that will shape our understanding of the natural world and drive innovation across industries.