·When people can further observe or manipulate the motion of electrons, they will gradually find that people are slowly trying to open an era of attosecond chemistry.

·Basic research requires flexible thinking and a broad vision. You can’t dance within rules and regulations, and you can’t innovate by following the rules, but you can’t have no boundaries at all, because research will go astray.

Gong Xiaochun introduced the attosecond cluster coincidence measurement system at the State Key Laboratory of Precision Spectroscopy Science and Technology, East China Normal University.

An attosecond is a very small unit of time, equivalent to 10 minus 18 seconds. With the help of attosecond light sources, people's field of view to study the structure of matter is expanding from the atomic and molecular level to the subatomic scale, so as to directly observe and even manipulate the attosecond motion of electrons. "When people can further observe or manipulate the motion of electrons, they will gradually find that people are slowly trying to open an era of attosecond chemistry." East China Normal University (hereinafter referred to as East China Normal University) State Key Experiment of Precision Spectroscopy Science and Technology Gong Xiaochun, a researcher of the laboratory, said in an exclusive interview with The Paper (www.thepaper.cn) a few days ago.

In August of this year, Gong Xiaochun was selected as the winner of the "Shanghai Science and Technology Youth Leading Project 35" in recognition of his building the world's first attosecond cluster conformity measurement system, and innovatively proposed the attosecond cluster size resolution spectrum to fill the gap from isolated atoms. , Molecular to complex condensed matter electron attosecond dynamics precision measurement blank.

Filling the gap in precision measurement of attosecond dynamics

Attosecond coincidence measurement spectrum is one of the most advanced metrology in attosecond ultrafast optics. Since the attosecond light pulse, an important part of it, has been proposed, it has set off an ultrafast in the field of atomic, molecular and even condensed matter basic physics research. The measurement revolution.

In 2001, an international research team led by Prof. Ferenc Klaus from the Technical University of Vienna, Austria obtained the first laser with a pulse width of 650 attoseconds. Since then, the pulse width record of attosecond lasers has been continuously refreshed. In November 2017, the Federal Institute of Technology Zurich (ETH) announced that it had successfully shortened the pulse duration of an X-ray laser to 43 attoseconds, setting a world record for the shortest laser pulse duration.

The attosecond light source expands people's field of view to study the structure of matter from molecules to the interior of atoms. It is expected to reproduce the physical images of electron motion at the atomic scale inside the matter in "slow motion" by means of high-speed photography, so that humans can use extremely high time. The resolving power reveals the dynamic characteristics of electrons, and provides new research methods and important innovation opportunities for the development of physics, chemistry, biology, materials, information and other fields.

Gong Xiaochun, researcher at the State Key Laboratory of Precision Spectroscopy Science and Technology, East China Normal University

Gong Xiaochun introduced that electrons are like antennae in chemical reactions or life activities, which can transmit or transfer information energy. "In chemical reactions or life activities, electrons are the first to interact after different substances come into contact. Similarly, when light interacts with matter, it also interacts with electrons inside the matter first, and then transmits various information. "For example, after the sequence or basic unit of DNA in the water environment is irradiated with strong light or high-energy radiation, which is the first damage to DNA or water? Preliminary studies have shown that water is first ionized, and water releases low-energy electrons, which resonate with other bases to achieve charge transfer, break the hydrogen bond network, and even damage the surrounding base units.

The traditional idea is that the ionization process of electrons is instantaneous, but with the development of attosecond light pulse technology, researchers have found that this process is not instantaneous, and electrons need several attoseconds or even hundreds of attoseconds to traverse the electric field of atoms or molecules. .

Cluster is a new level of material structure between atoms, molecules and macroscopic solid matter, and it is a transitional state in which various substances are transformed from atoms and molecules to bulk matter. "The bottleneck of previous research is that researchers mainly use infrared, Raman, THz and other spectral methods to observe the structure and motion of nuclei in clusters. Time-resolved photoelectron spectroscopy has great limitations." In the aspect of second measurement spectroscopy, the world's first attosecond cluster coincidence measurement system has been designed and constructed. Through attosecond cluster size-resolved spectroscopy, researchers can accurately measure water clusters of different sizes at the single-molecule spatial scale and attosecond time scale. Interactions between electrons and parent-hole spatial delocalization at the moment of photoionization of clusters, revealing attosecond ultrafast measurements of the interaction between structural symmetry, disorder, and electron localized delocalization evolution in water clusters.

Attosecond spectroscopy is expected to lead the further exploration of novel phenomena and natural laws in attosecond optics and extreme strong field photophysics, and to achieve precise measurement and regulation of chemical reactions and electron ultrafast dynamics in complex condensed matter systems. "We are also continuously optimizing and transforming advanced extreme ultraviolet attosecond light sources and pump-detection delay lines with ultra-high time resolution. Based on this high-resolution detection clock, we can further explore the interior of special state systems such as superconductors and topological insulators. The complex electron dynamics process", Gong Xiaochun said.

Break the stereotype of foreign counterparts

When graduating from the Optical Information Science and Technology major of Ocean University of China, Gong Xiaochun did not know what scientific research was, and was only interested in ultrafast optics. In 2012, when the doctoral supervisor Prof. Wu Jian he chose just returned to China and was about to set up a laboratory, Gong Xiaochun followed his supervisor to study electron ion coincidence measurement. Treasure”, to master it and become the designer of the attosecond instrument system.

After graduating with a doctorate degree in 2017, Gong Xiaochun obtained the qualification to stay in school to study attosecond ultrafast optics, but felt that the work was a bit difficult and still needed to learn new knowledge. In 2018, he was a visiting student at the Department of Physical Chemistry at ETH Zurich. HJ Wrner, a professor in the Laboratory of Physical Chemistry at ETH Zurich, is good at attosecond spectroscopy. During Dr. Gong Xiaochun, he studied electron ion coincidence measurement. The two sides complement each other's advantages and explore new research: attosecond coincidence measurement technology.

The first step in the cooperation is to build a laboratory. Gong Xiaochun needs to develop an attosecond cluster conformity measurement system. During this period, Gong Xiaochun just stayed in the laboratory and worked hard every day. "Building the laboratory can not only give full play to what I have learned before, but also is the best time to learn and develop various new skills." As a result, Gong Xiaochun " Full Fire", the system was designed and built in less than a year. When he saw the water clusters and measured the attosecond electron process, the doctoral students and engineering technicians in the laboratory were amazed.

After Christmas that year, when Gong Xiaochun was about to leave ETH Zurich, the electrical engineer in the lab said to him, "At first I thought you would be like most people in this lab before, I didn't expect you The laboratory is done, and the instrument has measured very beautiful results." The other party promised that as long as Gong Xiaochun needs it in the future, he will give full support.

In 2019, after Gong Xiaochun returned to China, the attosecond cluster coincidence measurement system is still running stably in the laboratory of ETH Zurich for domestic and foreign researchers and new students to do experiments, measure data, and develop attosecond ultrafast optoelectronics. Research, and jointly promote the development of the discipline of attosecond ultrafast optics.

Innovation cannot dance within boundaries

After returning from Zurich, Gong Xiaochun further optimized and upgraded the attosecond cluster coincidence measurement system at the State Key Laboratory of Precision Spectroscopy Science and Technology, East China Normal University. When asked whether the achievements made in the research field of attosecond spectroscopy were accidental or inevitable, he replied: In research, you must constantly think about and innovate, "Once you find the main line, you will know how to do it. ."

When Gong Xiaochun was a doctoral student, he studied electron measurements and observed the motion of atomic nuclei, "At that time, there was no attosecond pulse method, and the time-frequency characteristics of the electron spectrum and the physical mechanism behind it were not clear. There is no way to carry out real-time observation." During the research process of attosecond photoionization, he always wanted to understand the interference mechanism of electrons, and it was not until the eve of his Ph.D. graduation that he found a breakthrough. "In the process of continuous data analysis and continuous thinking, the problems are I got the answer." During his Ph.D. study period, Gong Xiaochun was highly knowledge-intensive, and learned quickly. He published academic papers in "Physical Review Letters" many times, and received awards and funding from laboratories, schools, and the Optical Society. In the past few years, when few academic papers were published, he did not waste time, but continued to polish himself to supplement the shortcomings of learning experiments and theory.

As a postdoctoral fellow in Zurich, he felt that if he just followed the work of others to carry out research, it would be meaningless and must be innovative, so he set out to design and build an attosecond cluster conformity measurement system. When he returned to China to rebuild, he thought that there must be further breakthroughs, to explore advanced science and technology such as isolated attosecond pulses, and to study more complex and difficult scientific problems.

Gong Xiaochun said that basic research needs flexible thinking and a broad vision. "You can't dance within the rules and regulations. You can't innovate by following the rules, but you can't have no boundaries at all, because research will go wrong."

With flexible thinking and self-confidence, it is also necessary to have clear scientific research goals and scientific taste. "When you have enough ability to support doing this, the final state presented is very creative." He also said , Science does not depend on personal will, and scientific research should treat scientific issues with a scientific attitude and have integrity.

At present, Gong Xiaochun is developing an atomic demultiplexing interferometer based on the attosecond cluster coincidence measurement system, developing a method of atomic demultiplexing interference, distinguishing the composition of each electron, and observing the photoionization process of each component in an atomic state. time-frequency characteristics and correlations. He hopes to have more opportunities to explore new ideas for the design of advanced scientific instruments, achieve new breakthroughs in ultrafast physics research, challenge the limits of ultrafast physics measurement and its expansion and application in the field of attosecond ultrafast science. In the ultra-short time scale and ultra-high spatial resolution scale, it shows the non-equilibrium dynamics of the microscopic quantum physics world in the process of interaction between light and matter, and seeks the limit of physical property measurement and regulation. At the same time, it continues to condense core key technologies, form standardized and modular scientific instruments, and expand the trend of multidisciplinary integration. "As Mr. Yang Zhenning said, you have to have your own little luck. What is more advanced, what is more meaningful, what is more in your opinion, you want to stand with it, just like sunflowers like to chase In the sun, the grass always likes to grow in the sky, maybe this is the taste."

(Editor's note: This article is one of the series of "Zhengziguang: Shanghai Science and Technology Youth Leading Plan to Follow the Light" series jointly launched by The Paper and Shanghai Science and Technology. Please pay attention to more follow-up reports.)