In the past two years, the "contactless temperature measurement and security integrated machine" that has shown its skills in epidemic prevention and control has made many people re-recognize terahertz waves, and the study of "or will be the key technology of 6G communication" has made terahertz waves famous - terahertz waves have become a dazzling star in the electromagnetic spectrum.
People with a certain physical foundation know that in the electromagnetic spectrum, the terahertz band is a relatively special existence: it contains some millimeter waves, all submillimeter waves and some far-infrared, wavelengths from 3mm to 30μm, and frequencies covering 0.1THz to 10THz. Although humans discovered this band in astronomical research as early as a hundred years ago, due to the development of technology, research in related fields has been stagnant for a long time, and even until the 80s of the last century, terahertz did not have a name, but was classified into the category of "far infrared rays". It was not until the 90s, with the rise of a series of new technologies, especially the development of ultrafast laser technology, which provided a stable and reliable excitation light source for the generation of terahertz pulses, and the research around terahertz was carried out in depth.
It is found that because of transient, broadband, coherence, low energy and many other special properties, terahertz can be widely used in broadband communications, radar, electromagnetic weapons, electronic countermeasures, medical imaging, astronomy, non-destructive testing, safety inspection and other fields, and will bring subversive changes to many industries. In 2004, terahertz was named one of the "Top Ten Technologies Changing the World of Tomorrow" by the U.S. government. In 2005, Japan listed it as the first of the "Ten Strategic Goals of the National Pillar", and launched a nationwide effort to research and development - a wave of research targeting terahertz quickly swept the world.
Also in 2005, in the late autumn of the Beijing Xiangshan Hotel, the 270th symposium with the theme of "New Development of Terahertz Science and Technology" was held as scheduled. A number of domestic experts and scholars with far-reaching influence in the field of terahertz research conducted in-depth research and discussion on the development direction of mainland terahertz and formulated the development plan of terahertz technology. After the meeting, as a pioneer platform for terahertz research in China, the terahertz laboratory of Capital Normal University was identified as one of the national terahertz technology open research and development platforms, promoting the development of the mainland terahertz field and becoming an important mission of the laboratory.
As one of the core members of the terahertz laboratory, Zhang Yan, professor and doctoral supervisor of the Department of Physics of Capital Normal University, director of the Beijing Key Laboratory of Metamaterials and Devices, and deputy director of the Key Laboratory of Terahertz Optoelectronics of the Ministry of Education, has adhered to the scientific research idea of "research closer to application", and has promoted the continuous in-depth development of terahertz-related research, especially in the construction of terahertz imaging technology and sub-wavelength metal microstructure device characterization platform. Help the mainland terahertz scientific research work to move to one peak after another.
Thick and thin hair specialized in terahertz research
Zhang Yan's relationship with terahertz dates back to 2003. At that time, foreign terahertz technology research and development was in full swing, and the terahertz laboratory of Capital Normal University, which was engaged in related research in China, was only two years old and was still in the stage of crossing the river by feeling the stones. The addition of Zhang Yan is a great benefit for the laboratory that is extremely hungry for talents - this young man born in 1972, who was just over the age of standing, has a brilliant scientific research resume and achievements: he was admitted to the Department of Applied Physics of Harbin Institute of Technology at the age of 18; At the age of 22, he studied for a master's degree, during which he took the lead in the research of optical fractional Fourier transform in China together with his supervisor, paving the way for the use of optical fractional Fourier transform for information processing; At the age of 24, he entered the Institute of Physics of the Chinese Academy of Sciences to pursue a doctoral degree, became a proud protégé of Academician Yang Guozhen, and under the guidance of Academician Yang and researcher Gu Benyuan, he pioneered the application of fractional Fourier transform in the field of optical information processing; Due to his outstanding performance and research needs, in 1999, Zhang Yan went to Japan to study at Yamagata University, during which he began to engage in bioimaging research; After that, he moved to the Department of Electronic Engineering of the Hong Kong Polytechnic University as an associate researcher, engaged in the research of optical fiber gas sensors. In 2002, after receiving the support of the Humboldt Fund in Germany, Zhang Yan went to the Institute of Applied Optics of the University of Stuttgart to engage in scientific research.
Since he came into contact with physics research in 1990, Zhang Yan has been in many universities and scientific research institutions for more than ten years, constantly expanding the breadth of his scientific research direction. After growth and accumulation, he has a new idea of his scientific research path: "'If you don't get involved, you can't get through, and you can't do it without specialization', after more than ten years of experience, I have laid a solid foundation, should I go in the direction of specialization and do deep and solid in a certain direction?" Again, no matter how good it is abroad, there is always no feeling of home, or you should go back to China to do something. ”
Zhang Yan had in-depth communication with Academician Yang Guozhen about his ideas. Science has no borders, but scientists have borders, and Academician Yang strongly agreed with Zhang Yan's return to China to devote himself to scientific research, and warmly invited him to join the team he led to create, the Terahertz Laboratory of Capital Normal University. Years of scientific research experience made Zhang Yan keenly foresee the research value of terahertz, so he accepted the olive branch thrown by Academician Yang without hesitation, determined to make something new around terahertz.
Looking back on the initial time of devoting himself to terahertz research, Zhang Yan was deeply impressed: at that time, the laboratory was in its infancy, there was not much successful experience, nor sufficient funds, policy support, and even the terahertz signal could not be debugged for a while, "I remember that the laboratory was in a place like a workshop of more than 40 square meters, that is, we transformed theoretical things into practice step by step, and promoted the mainland terahertz research work to continue to go deeper."
Through practical exploration, Zhang Yan has a clearer definition of his scientific research path - first aiming at the target and then shooting arrows - which is a "German" scientific research model that has a profound impact on him during his study in Germany. Zhang Yan explained that "target" is application, "arrow" is research, the so-called "target first and then arrow" means that all research should be based on application. In Zhang Yan's view, unlike the traditional scientific research model of "first having a research topic, and then moving closer to the application", the scientific research model of "aiming at the target first and then shooting arrows" solves the worries of technical research at the beginning, avoids the potential risk of disconnection between research and application, and has more practical guidance value.
After determining the application-oriented scientific research ideas, Zhang Yan has been immersed in focusing on the relevant research of terahertz applications for decades, and has promoted the mainland terahertz research work to quickly catch up with the world level with fruitful results, and through continuous scientific and technological innovation, he has blazed a trail of characteristic terahertz research.
Fruitful Results: Serving the country's ideals with innovation
With the deepening of the study of the terahertz band, high-power terahertz light sources and stable terahertz pulse detection methods are becoming more and more mature, and various terahertz spectroscopy and imaging techniques have gradually become practical optical measurement methods. The focus of Zhang Yan's research is on the two major directions of spectroscopy and imaging technology. He said: "My idea is to apply the methods of spectroscopy and imaging characterization developed by terahertz to the characterization exploration of micro-nano devices." In this direction, Zhang Yan led the team to carry out in-depth research, including various improvements to improve the measurement accuracy of terahertz imaging systems, and the application of this imaging technology to research in different scientific research fields. He pioneered the organic combination of terahertz area array imaging and near-field detection technology to build the first terahertz quasi-near-field imaging system in China, thereby increasing the resolution of terahertz imaging by an order of magnitude and enhancing the practicality of the terahertz pulsed wave focal plane imaging system. At the same time, a variety of terahertz imaging methods such as multi-wavelength imaging, polarization imaging, and real-time tomography are also proposed, which continuously expand new ideas for terahertz imaging.
In addition, due to the important scientific significance and practical application value of the research of terahertz functional devices, Zhang Yan also focuses on the study of metal sub-wavelength structures and the interaction of semiconductor micro-nano structures with terahertz. With the funding of the "973" project of the Ministry of Science and Technology, Zhang Yan led the research group to develop his own finite time domain difference algorithm (FDTD), studied the dependence of the transmission characteristics of metal sub-wavelength structures on the shape, size, distribution of microstructures in the device and the characteristics of metal materials and substrate materials, and gave the influence analysis of the transverse groove structure in metal slits on the transmission characteristics: the conversion characteristics of some materials under external excitation were studied. And established the first set of terahertz focal plane imaging system for the characterization of sub-wavelength photonic devices in the terahertz band, put forward its own design method for terahertz metasurface devices, designed, prepared and characterized a series of terahertz metasurface devices, the thickness of the device is only one thousandth of the working wavelength, which provides a new idea for the integration of terahertz systems.
With the unremitting efforts of Zhang Yan and other scientific researchers, the Terahertz Laboratory of Capital Normal University has filled a number of gaps in the domestic terahertz field, become a leader in the field, continuously led and promoted the development of domestic terahertz science and technology, and successively undertaken a number of major national projects, solved a number of major national demand problems, driven the industrialization of domestic terahertz science and technology, and became a leading and internationally influential terahertz open R&D and innovation platform. It has made outstanding contributions to the realization of a strong country in science and technology.
As a core member of Beijing's "Terahertz Spectroscopy and Imaging" innovation team, Zhang Yan has also achieved great results. In the past ten years, he has participated in the writing of 5 academic monographs and published more than 380 related research papers, including more than 300 in SCI; At the same time, he has also won many honors such as Beijing Science and Technology Rising Star Program, New Century Outstanding Talents of the Ministry of Education, Beijing Changcheng Scholar, Beijing Millions of Talents Project, etc., and was co-opted as a fellow of the Optical Society of America. In addition, as a backbone teacher of young and middle-aged people in Beijing, he has worked tirelessly on the three-foot platform over the years, trained more than 40 graduate students and doctoral students, and made indelible contributions to building a high-tech talent team and promoting the strategy of strengthening the country with science and technology.
Meritorious and diligent. As a scientific research worker, over the years, Zhang Yan has been rooted in the field of optoelectronic scientific research, bravely climbing the peak of science through innovation and enterprising, and writing the ideals and feelings of a new generation of Chinese scientific research workers! For Zhang Yan, climbing mountains and rivers is just an ordinary thing, and what has always remained unchanged is the heart of scientific research to serve the country.