X-ray laser provides a window on cellular life

The world's third soft X-ray free-electron laser facility, based in Shanghai, recently achieved full coverage of the wavelengths of the "water window", which will allow scientists to observe live cells.

Observations of the characteristics, internal structure and dynamic changes of cells at the femtosecond level－a quadrillionth of a second－are expected to lead to new insights in live cell imaging and discoveries in materials research, physics, chemistry and biology, experts said.

The Shanghai Advanced Research Institute, which is affiliated with the Chinese Academy of Sciences, announced recently that the Shanghai Soft X-ray Free-Electron Laser has made important progress. It lased at wavelengths of 5.6 nanometers, 3.5 nm, 2.4 nm and 2.0 nm successively, achieving full coverage of the "water window"－a region of the electromagnetic spectrum in which water is transparent to soft x-rays.

"Among the three soft X-ray FEL facilities in the world, FLASH in Germany, FERMI-FEL in Italy and SXFEL in China, 2.0 nm is so far the best record," said Zhao Zhentang, an academician with the Chinese Academy of Engineering and the Shanghai Advanced Research Institute's vice-president. "The facility will function as a powerful tool for related scientific research in the country."

The institute said the facility will be open for use by both domestic and foreign scientists upon application. Some leading higher education institutions, such as Tsinghua University, the University of Science and Technology of China, Shanghai Jiao Tong University and ShanghaiTech University, have already taken part in the development of initial experimental stations.

Zhao explained that the "water window" is occupied by soft X-ray radiation with wavelengths ranging from 2.2 nm to 4.4 nm. At those frequencies, oxygen and water are transparent to X-rays, but other important elements such as carbon and nitrogen, the building blocks of life, still interact with them.

"This is an ideal tool for studying organic molecules and biological specimens in their natural aqueous environment, and thus is of great importance to scientific applications," said Zhao, who is also director of the Shanghai Synchrotron Radiation Facility and chief scientist of the SXFEL project.

Liu Bo, deputy director of the Shanghai Synchrotron Radiation Facility and a top-ranking deputy director of the SXFEL project, said that using an FEL light source with high brightness, ultrashort pulses and high coherence will allow researchers to study the functions and interactions of living cells and observe the subtle dynamic processes in chemical reactions.

"With previous technologies, scientists may only see the result of a chemical reaction," he said. "The facility can empower them to witness tiny steps in between the entire reaction precisely and that very likely will trigger new discoveries and enlightenment."

SXFEL, the first X-ray coherent light source in China, together with the Shanghai Synchrotron Radiation Facility, the Shanghai High Repetition Rate X-ray FEL and Extreme Light Facility, and the Shanghai Superintense Ultrafast Laser Facility, will form a cluster of facilities to support a photon science research center with global influence in Shanghai's Zhangjiang National Innovation Demonstration Zone, the Shanghai Advanced Research Institute said.