Content of SPECIAL TOPIC—Terahertz physics in our journal

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    Determination of potassium sorbate and sorbic acid in agricultural products using THz time-domain spectroscopy
    Yuying Jiang(蒋玉英), Guangming Li(李广明), Ming Lv(吕明), Hongyi Ge(葛宏义), Yuan Zhang(张元)
    Chin. Phys. B, 2020, 29 (9): 098705.   DOI: 10.1088/1674-1056/ab9f25
    Abstract729)   HTML    PDF (530KB)(143)      
    The aim of this study was to investigate the feasibility of detecting potassium sorbate (PS) and sorbic acid (SA) in agricultural products using THz time-domain spectroscopy (THz-TDS). The absorption spectra of PS and SA were measured from 0.2 to 1.6 THz at room temperature. The main characteristic absorption peaks of PS and SA in polyethylene and powdered agricultural products with different weight ratios were detected and analyzed. Interval partial least squares (iPLS) combined with a particle swarm optimization and support vector classification (PSO-SVC) algorithm was proposed in this paper. iPLS was used for frequency optimization, and the PSO-SVC algorithm was used for spectrum analysis of the preservative content based on the optimal spectrum ranges. Optimized PSO-SVC models were obtained when the THz spectrum from the PS/SA mixture was divided into 11 or 12 subintervals. The optimal penalty parameter c and kernel parameter g were found to be 1.284 and 0.863 for PS (0.551-1.487 THz), 1.374 and 0.906 for SA (0.454-1.216 THz), respectively. The preliminary results indicate that THz-TDS can be an effective nondestructive analytical tool used for the quantitative detection of additives in agricultural products.
    Symmetry-broken silicon disk array as an efficient terahertz switch working with ultra-low optical pump power
    Zhanghua Han(韩张华), Hui Jiang(姜辉), Zhiyong Tan(谭智勇), Juncheng Cao(曹俊诚), Yangjian Cai(蔡阳健)
    Chin. Phys. B, 2020, 29 (8): 084209.   DOI: 10.1088/1674-1056/ab9c0b
    Abstract698)   HTML    PDF (659KB)(185)      

    The advancement of terahertz technology in recent years and its applications in various fields lead to an urgent need for functional terahertz components, among which a terahertz switch is one example of the most importance because it provides an effective interface between terahertz signals and information in another physical quantity. To date many types of terahertz switches have been investigated mainly in the form of metamaterials made from metallic structures and optically-active medium. However, these reported terahertz switches usually suffer from an inferior performance, e.g., requiring a high pump laser power density due to a low quality factor of the metallic metamaterial resonances. In this paper, we report and numerically investigate a symmetry-broken silicon disk based terahertz resonator array which exhibits one resonance with ultrahigh quality factor for normal incidence of the terahertz radiations. This resonance, which can never be excited for regular circular Si disks, can help to realize a superior terahertz switch with which only an ultra-low optical pump power density is required to modify the free carrier concentration in Si and its refractive index in the terahertz band. Our findings demonstrate that to realize a high terahertz transmittance change from 0 to above 50%, the required optical pump power density is more than 3 orders of magnitude smaller than that required for a split-ring resonator (SRR) based terahertz switch reported in the literature.

    High performance terahertz anisotropic absorption in graphene-black phosphorus heterostructure
    Jinming Liang(梁晋铭), Jiangtao Lei(雷江涛), Yun Wang(汪云), Yan Ding(丁燕), Yun Shen(沈云), Xiaohua Deng(邓晓华)
    Chin. Phys. B, 2020, 29 (8): 087805.   DOI: 10.1088/1674-1056/ab9cbf