14:45 〜 15:00
▲ [24p-D214-7] Visualizing nanoscopic field distribution of whispering gallery modes in a dielectric sphere by cathodoluminescence
キーワード：whispering gallery mode, cathodoluminescence, scanning transmission electron microscopy
Guided light that circulates along the perimeter of a spherical or circular resonator by means of total internal reflection and returns in phase with path length that is equal to an integer multiple of the wavelength is referred to as whispering gallery modes (WGMs). Such modes have been receiving a great attention in especially sensing applications due to their remarkable properties in having high quality factor, tight confinement of modes, small mode volume, and strong evanescent field. However, optical field of the WGMs at the optical frequencies have not been yet visualized experimentally. In this study, we present the internal field distribution of the WGMs in a Si sphere, by resolving the angle and polarization in four-dimensional technique of cathodoluminescence-based scanning transmission electron microscopy (4D STEM-CL). Modes at each discrete resonant wavelength are also identified and labeled based on their radial order, angular order, and polarization field. Identification of the mode as well as visualization of the optical field at respective resonances are further compared with the theoretical calculation.