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

[ China Instrument Network Instrument Development ] In order to explore the nano world more intuitively, a large number of researchers are committed to the development of high time-space resolution micro-nano-detection technology, and the femtosecond-nano space-time is under the responsibility of Academician Gong Qihuang of Peking University School of Physics. The Resolving Optical Experiment System "The National Major Scientific Research Instrument Development Project is working around this goal. Recently, this major instrument project has made significant progress in achieving multi-dimensional detection of surface plasmons based on ultrafast photoelectron microscopy technology. The results were published in the November 19, 2018 issue of Manipulation of the dephasing. Time by strong coupling between localized and propagating surface plasmon modes).

Figure 1 (a) Schematic diagram of photoelectron microscopy and multilayer structure, (b) Far-field and near-field detection curves, localized surface plasmon pattern distribution recorded by photoelectron microscopy under different wavelength laser excitation

Localized surface plasmons based on metal nanoparticles are widely used in different fields due to their high local intensity, small local scale, and high sensitivity. However, the ultra-short mode dephasing time of several femtoseconds greatly limits the breadth and practicality of its application. The multi-layer structure of this work design achieves strong coupling of local surface plasmons and propagation surface plasmons [Fig. 1(a)].

The dynamic numerical simulation results also clearly demonstrate the energy exchange between the local surface plasmon mode and the propagation surface plasmon mode under strong coupling. In the near field, the photoelectron microscope directly images the surface plasmon mode, which greatly breaks through the limitations of the original far-field detection technology, and combines different excitation sources to achieve different dimensions. Combined with the wavelength-adjustable laser source, the intensity evolution of the surface plasmon mode with wavelength in the frequency domain recorded by the photoelectron microscope is shown in the figure below [Fig. 1(b)].

Combined with ultra-fast pump detection technology, photoelectron microscopy records the evolution of surface plasmon mode over time in time domain. This work more deeply and intuitively detects the energy conversion process in the strong coupling system, and realizes the control of the mode life through the change of the detuning amount in the strong coupling. Compared with the uncoupled local surface iso-isolation mode, the strong coupling mode The lifetime is increased from 6 femtoseconds (10-15 seconds) to 10 femtoseconds. This research has important guiding value for further development of artificial photosynthetic, biosensing and other applications based on surface plasmons.

The research was completed by Peking University and Hokkaido University in Japan. Yang Jingwei, a Ph.D. student at the School of Physics of Peking University, and Sun Quan, an international collaborator of major instrument projects, and assistant professor of Hokkaido University, are the co-first authors of the article, Gong Qihuang and Hokkaido. Professor Misawa University is the co-author of the correspondence. In addition to the National Science and Technology Fund Committee's national major scientific research instrument development project, the work also received the Ministry of Science and Technology, Peking University National Center for Artificial Microstructure and Mesoscopic Physics, Extreme Optics Collaborative Innovation Center, "2011 Plan" quantum material science collaborative innovation Support from the Center, the Ministry of Education, the Ministry of Education, the Ministry of Science and Technology, and the Nanotechnology Platform of Hokkaido University. At present, the development of the national major scientific research instrument development project "Femtosecond-nano space-time optical experiment system" is progressing in an orderly manner, and a number of phased achievements including this work have been obtained.

The core instrument of the experimental system is a photoelectron microscope (PEEM) with low-energy electron microscopy, which emits light with wavelengths ranging from extreme ultraviolet to near-infrared. In the next step, the experimental system is expected to play an active role in research fields such as two-dimensional materials, photovoltaic materials and 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)