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Title
Japanese: 
English:Near-field infrared investigations of an arm-terminated spiral structure with bow-tie probe 
Author
Japanese: 岡本 拓也, 菅谷 俊夫, 藤村 直紀, 石川 昂, 河野 行雄.  
English: Takuya Okamoto, Toshio Sugaya, Naoki Fujimura, Kou Ishikawa, Yukio Kawano.  
Language English 
Journal/Book name
Japanese: 
English:Journal of Physics Communications 
Volume, Number, Page Volume 2    Number 10   
Published date Oct. 4, 2018 
Publisher
Japanese: 
English:IOP Publishing Ltd 
Conference name
Japanese: 
English: 
Conference site
Japanese: 
English: 
Official URL http://iopscience.iop.org/article/10.1088/2399-6528/aadec3
 
Abstract A detailed analysis of micro- and nanoantennas is crucial for enhancing the performance of photodetectors in the mid- and far-infrared (IR) region. In contrast to the rapid progress in IR detectors based on nanodevices, the local nanoscale properties of antennas for the purpose of near-field coupling with these detectors have not been well investigated. In this work, we fabricated and studied a logarithm-spiral (log-spiral) antenna with an arm termination, which was designed as a low-loss, wide-band antenna for highly efficient near-field interaction with nanoscale IR detectors. By using a scattering-type near-field optical microscope (s-SNOM) combined with a highly stable quantum cascade laser, we observed a nanoscale spatial distribution of amplitudes generated via IR illumination on the antenna surface. Experimental and simulated results revealed a clear dependence on IR-light polarization corresponding to the rotationally symmetric structure of the spiral antenna. Furthermore, phase mapping measurements indicated a π reversal of the out-of-plane phase between two adjacent antenna probes regardless of polarization direction, providing a possibility of efficient near-field coupling with nanoscale detectors. These results demonstrate that s-SNOM imaging offers a powerful tool for gaining useful information regarding mutual coupling between optical antennas and nanostructures.

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