Progress in the project of femtosecond-nano space-time resolution optical experiment system

Figure 1: (a) Schematic diagram of photoelectron microscopy and multilayer structure; (b) Far-field and near-field detection curves, showing the distribution of localized surface plasmon patterns recorded under different laser wavelengths.

Localized surface plasmons, based on metal nanoparticles, have found widespread applications due to their high local intensity, small scale, and sensitivity. However, their ultra-short dephasing time—on the order of a few femtoseconds—has limited their practical use. In this study, a multi-layer structure was designed to achieve strong coupling between localized and propagating surface plasmons [Fig. 1(a)].

Dynamic numerical simulations clearly show energy exchange between the localized and propagating surface plasmon modes under strong coupling. Using a photoelectron microscope, researchers directly imaged the surface plasmon mode in the near field, overcoming the limitations of traditional far-field detection methods. By combining different excitation sources, they achieved multi-dimensional imaging. With a wavelength-tunable laser source, the photoelectron microscope recorded the intensity evolution of surface plasmon modes across different frequencies [Fig. 1(b)].

Combined with ultrafast pump-probe technology, photoelectron microscopy captures the temporal evolution of surface plasmon modes. This work provides a deeper and more intuitive understanding of energy transfer in strongly coupled systems and demonstrates how the mode lifetime can be controlled by adjusting the detuning in the coupling. Compared to the uncoupled localized mode, the strongly coupled mode's lifetime increased from 6 to 10 femtoseconds. This research holds great significance for future developments in artificial photosynthesis, biosensing, and other surface plasmon-based applications.

The research was conducted by Peking University and Hokkaido University in Japan. Yang Jingwei, a Ph.D. student at Peking University’s School of Physics, and Sun Quan, an international collaborator and assistant professor at Hokkaido University, are co-first authors of the paper. Gong Qihuang from Peking University and Professor Misawa from Hokkaido University are co-corresponding authors. The work was supported by multiple institutions, including the National Science and Technology Fund Committee, the Ministry of Science and Technology, Peking University’s National Center for Artificial Microstructure and Mesoscopic Physics, the Extreme Optics Collaborative Innovation Center, the “2011 Plan” Quantum Material Science Collaborative Innovation Center, the Ministry of Education, and the Nanotechnology Platform at Hokkaido University.

Currently, the development of the national major scientific research instrument project, "Femtosecond-Nano Space-Time Optical Experimental System," is progressing smoothly, with several key achievements already realized. The core instrument of the system is a low-energy electron microscope (PEEM), capable of emitting light from extreme ultraviolet to near-infrared wavelengths. In the future, the system is expected to play a crucial role in fields such as two-dimensional materials, photovoltaic devices, and surface mesoscopic physics.

(Original title: "Extreme Optical Innovation Research Team 'Femtosecond-Nano Space-Time Discrete Optical Experiment System' National Major Scientific Research Instrument Development Project Has Made Important Progress")