Enhancement of spatial resolution of terahertz imaging systems based on terajet generation by dielectric cube
Enhancement of spatial resolution of terahertz imaging systems based on terajet generation by dielectric cube
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DOI：
10.1063/1.4983114
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发表时间：
2017-05-01
期刊：
影响因子：
5.6
通讯作者：
Minin, Igor Vladilenovich
中科院分区：
文献类型：
--
作者：
Hai Huy Nguyen Pham;Hisatake, Shintaro;Minin, Igor Vladilenovich
太赫兹（THz，0.1-10 THz）区域因其在生物医学、材料检测和无损成像等实际应用中的潜力而吸引了巨大的研究兴趣。这些应用需要增强特定感兴趣频率的空间分辨率。人们已经提出了多种分辨率增强技术，例如近场扫描探针、表面等离子体激元和非球面透镜。在这里，我们首次证明，只需将中尺度介电立方体放置在连续波太赫兹成像系统的聚焦成像点上，即可将其用作新型分辨率增强器。该增强器的工作原理基于电介质长方体生成所谓的太赫兹射流，即太赫兹区域的光子射流。通过将折射率为 1.46 的聚四氟乙烯立方体放置在成像系统的成像点处，无论数值孔径 (NA) 是多少，都可以获得亚波长热点。使用我们独特的太赫兹波可视化系统对 125 GHz 产生的太射流进行了实验表征。将增强器放置在测得的NA为0.55的反射镜焦点处所获得的热点半高全宽(FWHM)约为0.55 lambda，这甚至比空气中理想最大数值孔径(NA = 1)的传统聚焦装置所获得的FWHM还要好。展示了 Suica 集成电路卡（日本火车通用票价卡）和带有 0.63 lambda 沟槽的铝板的无损亚波长分辨率成像演示。使用增强器在125 GHz下获得的幅度和相位图像可以清楚地分辨出铝板上的空气沟槽和卡的内部电子电路，而没有使用增强器获得的图像由于分辨率不足而变得模糊。使用增强器还使图像对比度增加了 4.4 倍。 (C) 2017 年作者。
The terahertz (THz, 0.1-10 THz) region has been attracting tremendous research interest owing to its potential in practical applications such as biomedical, material inspection, and nondestructive imaging. Those applications require enhancing the spatial resolution at a specific frequency of interest. A variety of resolution-enhancement techniques have been proposed, such as near-field scanning probes, surface plasmons, and aspheric lenses. Here, we demonstrate for the first time that a mesoscale dielectric cube can be exploited as a novel resolution enhancer by simply placing it at the focused imaging point of a continuous wave THz imaging system. The operating principle of this enhancer is based on the generation-by the dielectric cuboid-of the so-called terajet, a photonic jet in the THz region. A subwavelength hotspot is obtained by placing a Teflon cube, with a 1.46 refractive index, at the imaging point of the imaging system, regardless of the numerical aperture (NA). The generated terajet at 125 GHz is experimentally characterized, using our unique THz-wave visualization system. The full width at half maximum (FWHM) of the hotspot obtained by placing the enhancer at the focal point of a mirror with a measured NA of 0.55 is approximately 0.55 lambda, which is even better than the FWHM obtained by a conventional focusing device with the ideal maximum numerical aperture (NA = 1) in air. Nondestructive subwavelengthresolution imaging demonstrations of a Suica integrated circuit card, which is used as a common fare card for trains in Japan, and an aluminum plate with 0.63 lambda trenches are presented. The amplitude and phase images obtained with the enhancer at 125 GHz can clearly resolve both the air-trenches on the aluminum plate and the card's inner electronic circuitry, whereas the images obtained without the enhancer are blurred because of insufficient resolution. An increase of the image contrast by a factor of 4.4 was also obtained using the enhancer. (C) 2017 Author(s).