Hikaru Saito
Kyushu University
Dr. Hikaru Saito was received his PhD in science from Kyoto University, Japan, in 2014. He is now an assistant professor of Kyushu University in Japan. His research interest includes electron microscopy and plasmonics.
The use of surface plasmon-polartons (SPPs) is one of the most promising ways to achieve nano-cavities with ultra-small mode volumes, leading to enhanced spontaneous emission and nanolasers. We have performed a detailed characterization of a plasmonic crystal (PlC) cavity, and visualize standing plasmonic waves localized inside the cavity by using angle-resolved cathodoluminescence (CL) technique combined with scanning transmission electron microscopy (STEM) [1]. The investigated PlC cavity was composed of silver pillar arrays with a square lattice. An angle-resolved spectroscopy (ARS) pattern indicates a plasmonic bandgap at the Γ point in the crystalline area (Fig. 1a), where SPPs are forbidden to propagate in the PlCs. In the ARS pattern taken from the cavity area sandwiched by two PlCs, an energy level is observed in the energy range of the crystalline bandgap (Fig. 1b). To identify the character of the new mode appearing in the bandgap, we have performed photon map imaging around the cavity area (Fig. 1c and 1d), indicating the new mode is confined in the cavity.
In detailed analyses about dependence of the cavity mode on the cavity width (W), the modal symmetry and the quality factor showed periodic changes as a function of W, and these behaviors were related to the characteristics of the band-edge modes. As a result, the formation mechanism of the cavity mode has been elucidated, which provides a clear design guide for the PlC cavity to control the coupling between SPPs and photons in plasmonic devices.
This work was supported by the Japanese Ministry of Education, Culture, Science, and Technology (MEXT) Nanotechnology Platform 12025014.
[1] H. Saito and N. Yamamoto, Nano Lett. 15, 5764–5769 (2015).
