Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 61775021, 91850109, 11474040, 62005022, 12004052), the Education Department of Jilin Province Foundation (Grant No. JJKH20190555KJ), the Department of science and technology of Jilin Province Foundation (Grant Nos. 20200201268JC, 20200401052GX), and the China Postdoctoral Science Foundation (Grant No. 2019M661183)
Received Date:02 November 2020
Accepted Date:22 December 2020
Available Online:10 May 2021
Published Online:20 May 2021
Abstract:Near-field imaging and active control of excitation efficiency of femtosecond propagating surface plasmon (fs-PSP) are the prerequisites for its application. Here, we perform near-field imaging of fs-PSP excited at the trench etched on silver nano-film by using photoemission electron microscopy (PEEM). As an excellent near-field microscopy technique of in situ imaging with a high spatial resolution (< 20 nm), it needs neither molecular reporters nor scanning probes as required in nonlinear fluorescence microscopy in nonlinear fluorescence microscopy or scanning near-field optical microscopy, both of which may potentially bias PSP derived from such measurements. The period of the interference patterns induced by the incident femtosecond laser and the laser-induced fs-PSP and the wavelength of fs-PSP in a range of 720–900 nm of the incident laser wavelength are systematically measured. The fringe period of the interference pattern between fs-PSP and the incident laser is a range of 5.9–7.7 μm, and the wavelength of fs-PSP is in a range of 700–879 nm. The experimental results are consistent with the theoretical simulation results. Furthermore, we demonstrate that the excitation efficiency of fs-PSP can be actively controlled by adjusting the polarization direction of the incident laser in the femtosecond pump-probe experiments. Specifically, it is found that when the incident laser is polarized to 0° (p-polarization light), the excitation efficiency of PSP reaches a maximum value, and when the incident light is polarized to 90° (s-polarization light), the excitation efficiency of fs-PSP is the lowest. Unlike the simulation result by the finite difference time domain (FDTD) method, a plateau area of the intensity of the photoemission signal with the polarization direction of the incident laser appears in the femtosecond pump-probe experiment. This phenomenon is attributed to the background noise of the detection laser that masks the change of the fs-PSP excitation efficiency. In a word, this research realizes the experimental measurement of the basic parameters of fs-PSP and the manipulation of fs-PSP excitation efficiency by adjusting the polarization angle of the incident laser. This research lays a foundation for realizing the engineering manipulation of fs-PSP excitation efficiency and optimizing the performance of plasmonic devices. Keywords:photoemission electron microscopy/ femtosecond propagating surface plasmon/ near-field imaging/ regulation of excitation efficiency