Abstract-Control of Spoof Localized Surface Plasmons Using Terahertz Near-field Microscope

Takashi Arikawa, Shohei Morimoto, Tomoki Hiraoka, François Blanchard, Kyosuke Sakai, Keiji Sasaki, and Koichiro Tanaka

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=2704300894288992135

We performed time-resolved terahertz near-field imaging of a gold disk with sub-wavelength periodic grooves and successfully observed spoof localized surface plasmons. A selective excitation method is also demonstrated with orbital angular momentum of light.

© 2018 The Author(s)

Abstract-Focusing light with orbital angular momentum by circular array antenna

Takashi Arikawa, Shohei Morimoto, and Koichiro Tanaka

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-12-13728&origin=search

We experimentally demonstrated focusing of light with orbital angular momentum (OAM) using an 8-element circular array of linear antennas. A spiral phase plate was used to generate a vortex beam with an OAM of ħ in the terahertz (THz) frequency region. We used THz near-field microscope to directly measure the phase vortex. A beam profile with a center dark spot and 2π phase rotation was observed in the small center gap region of the circular array antenna after the vortex beam excitation. The beam size is reduced by a factor of 3.4 ± 0.2. Half-wave resonance of the antenna element is responsible for the focusing function, indicating the scalability of this method to other frequency regions. This method will enable deep subwavelength focusing of light with OAM and eliminate the obstacle for the observation of the dipole forbidden transition with finite OAM of the vortex beam.

© 2017 Optical Society of America