The research of miniaturized free electron coherent light source in China has made a breakthrough It will expand its application in the fields of spectral detection, sensing and information processing

On November 3, the journal Nature published the latest achievements made by Li Ruxin, academician of the Chinese Academy of Sciences and researcher of the State Key Laboratory of Strong-field Laser Physics, Shanghai Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, and his team in the field of miniaturized free electron coherent light sources.

In the experiment, the research team explored the kinetic process of plasmons (SPP) on the surface of femtosecond laser-driven ultrashort electron pulse pumping, and elaborated the stimulated amplification mechanism of free electrons and SPP by observing the dynamic process of coherent amplification of SPP pumped by free electron pulse.


Field (second from right) and research team Photo courtesy of respondents

“This research focuses on the fundamental study of the role of free electrons and surface-mode light fields, and in scientific principles, we innovatively discovered the process by which surface-mode light waves undergo coherent amplification and evolve into lasers.” Tian Ye told China Science News, “Because this process cannot be observed inside a gain medium such as crystals, we use ultrafast light technology to realize the detection of how surface light waves undergo ‘stimulated radiation light amplification’, that is, the process of laser generation in physical space.” ”

Looking back at the development history of lasers, increasing the radiation power of lasers, pursuing a wider tunable spectrum, and realizing smaller and lower cost light sources have long been the unremitting pursuit of laser science.

Common laser devices, such as ruby lasers, generally rely on gain media such as optical crystals to achieve laser output. The light source based on free electron radiation can be free from the constraints of crystals or other gain media, which can not only produce free space light radiation, but also form a kind of light source bound to the light field mode on the waveguide surface.

Compared with the light field propagating in free space, the surface light field represented by SPP has excellent characteristics of sub-wavelength compression and near-field enhancement, and has been gradually applied to a new generation of wireless communication, nanoscale imaging and detection and many other fields in recent years, and is expected to bring revolutionary technology to the development of integrated optoelectronic devices and the application of spectral detection, sensing, information processing and other fields.

At present, there are two main ways to generate surface light fields in the world: electron direct excitation and waveguide coupling, but no matter which way, the surface light field generated is limited by the weak light field energy caused by low coupling efficiency, which limits the application of SPP in the above fields. Therefore, the development of coherent high-power SPP light sources is an urgent problem to be solved in this field.

In recent years, the micro-nano manufacturing process, which is the basis of semiconductor integrated circuits, has been continuously improved, making it possible to integrate free electron light sources. Focusing on the miniaturized free electron coherent light source, the research team carried out the research on ultrashort electron pulse pumped SPP seeds driven by femtosecond lasers, and observed the coherent amplification of SPP by free electron pulses using ultrafast optical pumping-detection technology. By recording the spatiotemporal waveform, energy and spectrum of the electromagnetic field of SPP, the kinetic process of stimulated radiation amplification of SPP is dynamically demonstrated for the first time, and it is revealed that SPP has undergone three stages of stimulated radiation light amplification process in high-gain free-electron lasers, including superradiation, exponential growth and saturation.


Miniaturized free electron coherent light source Courtesy of respondent

This research innovatively develops a free electron pump to achieve SPP coherent amplification path, and verifies the surface mode light of plasmon, which can be pumped by free electron, and realizes coherent amplification.

“This opens up a completely new technical approach to the light source of high-brightness surface plasmons (surface light).” Tian Ye added, “This technology is of great significance for the development of miniaturized/integrated coherent light sources, and has important application value in the fields of integrated optoelectronic devices, sensing, and communications.” ”

According to the reviewers: “This work is very original, and its research results will arouse great research interest in various disciplines such as laser optics, nanophotonics and solid-state physics… The analysis shows that under more favorable conditions, even laser-like power amplification can be achieved, which shows very good application prospects. ”

In the field of miniaturized free electron light sources, the team has a long period of accumulation. In 2017, they discovered the radiation of a miniature electronic undulator, which was later selected as one of the “Top Ten Progress in Chinese Optics in 2017”. In 2020, the team discovered new principles such as laser modulation of attosecond electron pulse sequences and published them in Nature Photonics, and has since been rated as “Top Ten Advances in Chinese Optics in 2021”.

“In the future, based on this new technology, we will further develop miniaturized/integrated coherent light sources and expand their cross-application in the fields of spectral detection, sensing, and information processing.” Field said. (Source: China Science News, Zhang Shuanghu, Huang Xin)

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