Abstract- Near-Field nanoscopy of current-induced excess noise in graphene

K.-T. Lin,  Q. Weng, H. Nema,  S. Kim,   K. Sugawara,  T. Otsuji,  S. Komiyama,   Y. Kajihara

http://ieeexplore.ieee.org/document/8067243/

We describe a near-field nanoimaging method employed to spatially map the current-induced excess noise occurring in a bilayer graphene constriction with passive scanning near-field microscope (s-SNOM). We find that the excess noise, manifesting itself as fluctuating electromagnetic evanescent fields generated on the sample surface, is discernible only in the constricted region and increases linearly with increasing current. The passive s-SNOM thus proves to be a unique non-invasive experimental tool for investigating the electron transport mechanism via noise mapping in graphene device at the nanometer scale

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

Abstract-Plasmonic corrugated cylinder–cone terahertz probe

Haizi Yao and Shuncong Zhong  »View Author Affiliations

JOSA A, Vol. 31, Issue 8, pp. 1856-1860 (2014)
http://dx.doi.org/10.1364/JOSAA.31.001856

The spoof surface plasmon polariton (SPP) effect on the electromagnetic field distribution near the tip of a periodically corrugated metal cylinder–cone probe working at the terahertz regime was studied. We found that radially polarized terahertz radiation could be coupled effectively through a spoof SPP into a surface wave and propagated along the corrugated surface, resulting in more than 20× electric field enhancement near the tip of probe. Multiple resonances caused by the antenna effect were discussed in detail by finite element computation and theoretical analysis of dispersion relation for spoof SPP modes. Moreover, the key figures of merit such as the resonance frequency of the SPP can be flexibly tuned by modifying the geometry of the probe structure, making it attractive for application in an apertureless background-free terahertz near-field microscope.

© 2014 Optical Society of America