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Research progress of imaging technology based on terahertz quantum well photodetector
  • Abstract

    Terahertz (THz) waves have a good transmissivity through non-polar materials, and have no ionization effects on biomedical tissues. Therefore, it is ideal for the applications such as non-destructive testing and biomedical imaging. The imaging system based on THz quantum well photodetectors (THz QWPs) has higher imaging resolution, faster imaging speed, higher signal-to-noise ratio, and more compact structure than the imaging systems based on other detectors, as the THz QWPs have fast response, high responsivity, low noise equivalent power, and tiny size. This paper reviews the research progress of the imaging technology based on THz QWPs. And the factors affecting the core indicators of the imaging system are analyzed and summarized. Using more stable fixtures to mount the THz QWPs, improving the device response speed, detection sensitivity, array size, can improve the key performance of imaging systems effectively.

    Keywords

  • Figure 1. (a) Device schematic; (b) Band profile of an n-type GaAs/(Al, Ga)As 45° facet coupled THz QWP[10]
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    (a) Device schematic; (b) Band profile of an n-type GaAs/(Al, Ga)As 45° facet coupled THz QWP[]

    Detectors NEP/(pW/Hz0.5) Response time/s Frequency/THz
    Golay cell, typical ~140 > 0.03 0.04~20
    VOx bolometers ~40 > 0.01 1.0~10
    LiTiO3 pyroelectric detectors ~400 > 0.01 0.2~30
    Schottky barrier diodes ~100 10-10 0.1~10
    Superconducting hot electron bolometers 0.1 times the quantum limited ~2×10-10 0.1~10
    Si bolometers ~0.1 > 0.025 0.15~20
    Pair-breaking detectors Close to quantum limit ~2×10-10 < 2.0
    Glow discharge detector 12600 ~10-3 0.1~0.25
    Terahertz quantum well photodetector ~0.1 ~10-10 1.5~7.6 & 8.8~20.5
    CSV Show Table

    THz量子阱探测器(quantum well photodetectors,QWP)是基于GaAs/(Al, Ga)As量子阱子带跃迁的一种器件(器件如图 1(a)所示)。器件工作原理如图 1(b)所示,太赫兹光照之前,电子被束缚在量子阱中,当太赫兹光照射THz QWP时,束缚态电子吸收光子并被激发到第一激发态,成为连续态的自由电子,自由电子运动到达接触层形成光电流,从而实现对太赫兹光的探测。自2004年,加拿大国家实验室的刘惠春与中国科学院上海微系统所的曹俊诚等人联合研制出第一个THz QWP[]以来,国内外多个研究小组对该器件的材料设计[-]、响应率[-]、响应速度[-]、暗电流[-]、光电流谱[-]、电磁调谐[, -]等进行了系统研究。经过系列优化,目前峰值频率设计误差在10%以内[],最优响应率5.5 A/W[],最快响应速度6.2 GHz[],最佳噪声等效功率:~10-13 W/Hz0.5[],光谱峰值4.5 THz~6.5 THz连续可调[]。相比其他典型THz探测器(表 1所示)而言,THz QWPs兼具噪声等效功率小、响应速度快、全固态、器件工艺成熟等优点,非常适合用于THz成像。

    太赫兹波(Terahertz,THz)成像技术是THz领域中最重要的研究方向之一[]。自1995年,Hu等人首次实现THz成像演示实验[],该技术得到了各国研究人员广泛的关注和重视,并且在天文观测、人体安检、医学成像、无损检测等多个应用领域均取得了重要进展[-]。随着这些应用的发展,对探测器提出了等效噪声功率小、响应速度快、紧凑性好、廉价等要求。

    目前,已经有不少基于THz QWP的成像演示实验,按照光机扫描方式主要分为:二维栅格扫描成像、三维断层扫描成像、二维阿基米德螺线扫描成像、共聚焦扫描成像、无像素成像等几种主要方式。我们将对上述成像方式进行逐一介绍。

    2013年,谭智勇等人设计了一种THz QWP作为成像探测器,THz量子级联激光器(quantum cascade lasers, QCL)作为辐射源,移动成像物体进行二维栅格扫描的透射成像系统(如图 3(a)所示)[]。THz QWP性能与图 2中一致;THz QCL激射频点:3.9 THz,焦点光斑尺寸:0.625 mm(横轴)/0.813 mm(纵轴)。如图 3(b)对一张100元人民币的水印区域进行成像,成像结果如图 3(c)所示,成像区域:33 mm×52 mm,扫描步进:0.5 mm,总像素:7035,成像分辨率:0.5 mm,信噪比:~100,成像时间:180 min。该实验是首个基于THz QWP与THz QCL的联动成像演示,证明了基于THz QWP成像时,使用匹配的大功率高质量光源将大幅提升成像信噪比和分辨率。

    2012年,周涛等人设计了一种THz QWP作为成像探测器,商用标准黑体作为辐射源,移动成像物体进行二维栅格扫描的透射成像系统(如图 2(a)所示)[]。THz QWP峰值频点:3.2 THz,峰值响应率:0.5 A/W,比探测率:1011 cm·Hz0.5/W,工作温度~3.4 K;标准黑体辐射温度:300 K~473 K,辐射孔径:60 mm。如图 2(b)所示,使用该系统对一个隐藏信封中的钥匙进行成像(成像区域:25 mm×45 mm,扫描步进:1 mm,总像素:1125,成像分辨率:1 mm~1.2 mm,成像时间:30 min),当黑体温度分别为473 K,423 K,373 K时得到信噪比分别为27,17,10。该实验是首个基于THz QWP的成像演示,证明了基于THz QWP的成像方法是可行的。

    Figure 2. (a) Setup of the THz raster scanning transmission imaging system (with a blackbody as the source); (b) Comparison of visible image (top) and THz images for the hidden metal key with different SNR: 27, 17, and 10 (from top to bottom)[40]
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    (a) Setup of the THz raster scanning transmission imaging system (with a blackbody as the source); (b) Comparison of visible image (top) and THz images for the hidden metal key with different SNR: 27, 17, and 10 (from top to bottom)[]

    Figure 3. (a) Setup of the THz raster scanning transmission imaging system (with a THz QCL as the source); (b), (c) Visible (b) and THz images (c) of the watermark region of a paper money[41]
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    (a) Setup of the THz raster scanning transmission imaging system (with a THz QCL as the source); (b), (c) Visible (b) and THz images (c) of the watermark region of a paper money[]

    Figure 5. (a) Setup of the THz raster scanning reflection imaging system (with mirrors moving); (b), (c) Visible (b) and THz images (c) of a commemorative badge of the 40th anniversary of the University of Chinese Academy of Sciences; (d), (e) Visible (d) and THz images (e) of three drops of water covered with the polyurethane (PU) insulation materials[43]
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    (a) Setup of the THz raster scanning reflection imaging system (with mirrors moving); (b), (c) Visible (b) and THz images (c) of a commemorative badge of the 40th anniversary of the University of Chinese Academy of Sciences; (d), (e) Visible (d) and THz images (e) of three drops of water covered with the polyurethane (PU) insulation materials[]

    Figure 4. (a) Setup of the THz raster scanning reflection imaging system (with sample moving); (b), (c) Visible (b) and THz images (c) of the surface of flash disk[42]
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    (a) Setup of the THz raster scanning reflection imaging system (with sample moving); (b), (c) Visible (b) and THz images (c) of the surface of flash disk[]

    2019年,邱付成等人设计了一种THz QWP作为成像探测器,THz量子级联激光器(QCL)作为辐射源,移动反射镜进行二维栅格扫描的反射成像系统(如图 5(a)所示)[]。THz QWP峰值频点:4.2 THz,峰值响应率:0.5 A/W,噪声等效功率:4×10-13 W/Hz0.5,工作温度5 K;THz QCL激射频点:4.3 THz。对如图 5(b)中国科学院成立40周年纪念徽章和图 5(d)聚氨酯材料内壁的水滴分别进行成像,THz成像结果分别如图 5(c)和如图 5(e)所示。两图成像区域:20 mm×30 mm,扫描步进:0.2 mm,总像素:15000,成像分辨率:0.52 mm,成像时间:~60 min。该实验表明,基于THz QWP进行反射扫描成像时,可以通过移动三维反射镜组实现对静止物体的THz成像。

    2014年,谭智勇等人设计了一种THz QWP作为成像探测器,THz量子级联激光器(QCL)作为辐射源,移动成像物体进行二维栅格扫描的反射成像系统(如图 4(a)所示)[]。THz QWP性能与图 2(a)中一致;THz QCL激射频点:3.9 THz,焦点光斑尺寸:0.6 mm(横轴)/0.59 mm(纵轴)。如图 4(b)对一个闪存的表面进行成像,成像结果如图 4(c)所示,成像区域:38 mm×20 mm,扫描步进:0.4 mm,总像素:4896,成像分辨率:0.4 mm,成像时间:90 min。该实验证明了基于THz QWP成像时,可以得到较高分辨率的成像结果。

    2012年,周涛等人设计了一种THz QWP作为成像探测器,THz量子级联激光器(QCL)作为辐射源,旋转和双向平移成像物体进行三维断层扫描的成像系统(如图 6(a)所示)[]。其中,THz QWP峰值频点:3.2 THz,峰值响应率:0.5 A/W,比探测率:1011 cm·Hz0.5/W,工作温度~3.4 K与图 2(a)中一致;THz QCL激射频点:3.9 THz,焦点光斑直径:1.5 mm。如图 6(b)对一个放在白色塑料盒子里的离轴抛面镜进行成像,成像区域:85 mm×85 mm,扫描步进:1 mm,转向步进:12°,采集层数:24层,层间步进:1.2 mm,总采样:7225×24,信噪比:~600,成像时间:~24 h。该实验表明,基于THz QWP进行三维断层扫描成像时,成像结果与实际样品在定量上吻合较好,ART算法同样适用于THz波段,可在THz波段实现其他波段类似的断层扫描成像。

    Figure 6. (a) Setup of the THz 3D imaging system; (b), (c) Visible (b) and THz images (c) of a off-axis parabolic mirror[44]
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    (a) Setup of the THz 3D imaging system; (b), (c) Visible (b) and THz images (c) of a off-axis parabolic mirror[]

    Figure 7. (a) Setup of the THz archimedes spiral scanning imaging system; (b), (c) Visible (b) and THz images (c) of a leaf half covered with a plastic bag; (d), (e) Visible (d) and THz images (e) of a leaf covered with a polyethylene lid[45]
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    (a) Setup of the THz archimedes spiral scanning imaging system; (b), (c) Visible (b) and THz images (c) of a leaf half covered with a plastic bag; (d), (e) Visible (d) and THz images (e) of a leaf covered with a polyethylene lid[]

    2018年,邱付成等人设计了一种THz QWP作为成像探测器,THz量子级联激光器(QCL)作为辐射源,旋转和单向平移成像物体进行二维阿基米德螺线扫描的成像系统(如图 7(a)所示)[]。THz QWP和THz QCL性能参数与图 5(a)系统中器件性能一致。对一片塑料袋遮盖一半的叶子(如图 7(b))进行THz成像,成像结果如图 7(c)所示;对一片聚乙烯盖子完全遮盖的叶子(如图 7(d))进行THz成像,成像结果如图 7(e)所示。成像区域:直径100 mm,总像素:5000,成像分辨率:0.45 mm(横向)/0.3 mm(纵向),成像时间:5 s。该实验表明,基于THz QWP进行二维阿基米德螺线扫描成像时,避免了光机扫描系统的机械停顿,大幅提升了系统成像速度。

    Figure 8. (a) Setup of the THz confocal scanning imaging system; (b), (c) Visible image (b) of a plastic brush and THz image (c) of it fixed by the tape; (d), (e) Visible (d) and THz images (e) of a razor blade; (f), (g) Visible (f) and THz images (g) of a metal plate; (h), (i) Visible (h) and THz images (i) of a coin[46]
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    (a) Setup of the THz confocal scanning imaging system; (b), (c) Visible image (b) of a plastic brush and THz image (c) of it fixed by the tape; (d), (e) Visible (d) and THz images (e) of a razor blade; (f), (g) Visible (f) and THz images (g) of a metal plate; (h), (i) Visible (h) and THz images (i) of a coin[]

    2019年,邱付成等人在基于THz QWP作为成像探测器的二维阿基米德螺线扫描系统基础上,在光路中两处光斑焦点位置放置亚波长针孔(直径0.2 mm),从而同时实现共聚焦成像系统(如图 8(a)所示)[]。THz QWP和THz QCL性能参数与图 5(a)系统中器件性能一致。使用系统对图 8(b)塑料刷子、8(d)刮胡刀刀片、8(f)金属板、8(h)硬币分别进行成像,对应THz成像图分别为图 8(c)8(e)8(g)8(i)。成像区域:直径100 mm,成像分辨率:0.11 mm(横向)/0.32 mm(轴向),总像素:5000,信噪比:~125,成像时间:5 s。该实验表明,基于THz QWP进行共聚焦二维阿基米德螺线扫描成像时,可以同时获得高扫描速度和高空间分辨率。

    2016年,符张龙等人研制出堆叠生长THz QWP和发光二极管(LED)形成的THz频率上转换器件(THz QWP-LED),并使用该器件进行无像素成像[]。45°角耦合THz QWP-LED成像系统如图 9(a)所示,峰值频点:5.2 THz,峰值响应率:0.22 A/W,噪声等效功率:5.2×10-12 W/Hz0.5,工作温度~3.5 K;THz QCL激射频点:4.3 THz。图 9(b)为THz QWP-LED对THz QCL不同激射功率的成像结果,成像分辨率:优于0.05 mm,信噪比:优于10000,成像时间:1 s。目前,该类型正入射一维及二维金属光栅耦合器件均已经实现实时成像[],同时二维金属光栅耦合器件可以在10 μs内对THz QCL激射光斑的快速成像,成像光斑能量为高斯分布,与较长成像时间结果基本一致。该实验表明,基于THz QWP的频率上转换器件具备高分辨率、高速成像能力。

    Figure 9. (a) Setup for THz pixelless imaging system; (b) The focal laser spots of the THz QCL imaged by the THz QWP-LED[47]
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    (a) Setup for THz pixelless imaging system; (b) The focal laser spots of the THz QCL imaged by the THz QWP-LED[]

    THz QWP作为THz领域中紧凑、廉价、高响应率、低噪声的探测器,是适用于THz成像系统的理想接收器。表 2所列成像系统中直接透射和直接反射成像系统光路简单,但是成像时间较长,而且分辨率和信噪比均较低;3D成像系统可以得到物体3D信息,但是成像时间很长,而且成像分辨率和信噪比较低;阿基米德螺旋线扫描成像系统的成像时间短,但是分辨率仍然不高;共聚焦扫描成像系统的成像时间短,成像分辨率相对较高,但是成像信噪比较低;无像素成像系统,成像分辨率高,成像时间极短,而且成像信噪比高,是几种成像方式中最有前景的一种。

    从THz成像技术来说,必须开发高响应率、高探测灵敏度的探测器,以达到提升成像系统信噪比的目的。基于THz QWP成像系统关键性能参数如表 2

    Imaging type Frequency /THz Responsivity /(A/W) Detection array size/pixel Resolution/mm Imaging time Signal to noise ratio
    Transmission imaging 3.2 0.5 1 1~1.2 0.5 h 27/17/10
    3.2 0.5 1 0.5 3 h ~100
    Reflection imaging 3.2 0.5 1 ~0.4 1.5 h /
    4.2 0.5 1 0.52 1 h /
    3D imaging 3.2 0.5 1 1(x)/1.2(z) 24 h ~600
    Archimedes spiral scanning imaging 4.2 0.5 1 0.45(x)/0.3(y) 5 s /
    Confocal scanning imaging 4.2 0.5 1 0.11(lateral)/0.32(axial) 5 s ~125
    Pixel-less imaging 5.2 0.22 1 0.05 1 s ~10000
    CSV Show Table

    上述因素相互制约,必须依据实际应用需求进行一个综合权衡,来达到特定应用环境下的优化成像方案。当然,部分因素对所有核心指标提升均有帮助,如实验中采用更稳定的装置来固定光源和探测器,提升光源的出光稳定性、光束质量、功率等,提升探测器的响应速度、探测灵敏度、阵列规模等。相信随着源和探测器性能的持续提升,未来THz成像将变得更快(实时/超快)、更精确(高分辨率)和更简单(系统的低复杂性),将在生物医学成像和工业成像领域发挥重要作用。

    THz成像常见核心指标为成像分辨率、成像面积、成像速度和成像信噪比等。成像分辨率受到光学衍射极限和光路限制,光学衍射极限由工作频段决定,常规方式难以优化,只有通过共聚焦等手段优化;光路对分辨率限制体现在透镜或者反射镜的色散效应、聚焦能力等。成像面积主要受限于系统光路,可以通过设计实现大面积成像,但是成像面积大时必须保证扫描系统成像镜组移动时空抖动小,重复性好,才可获得较好成像。成像速度受限于扫描机制、信号采集时间、采样点规模、探测器规模,采用无需机械停顿的可以获取更高的采样速度,但是要求探测器具有高灵敏度及高响应速度;信号采集时间受限于探测器带宽,但是同样也需要探测器具有高灵敏度,否则无法获得较高信噪比图像;采样点数量增加,采样总时长增加,成像速度越慢;探测器规模越大,相同时间采样点数越多,采样速度越快。成像信噪比主要受系统光路稳定性、光源功率稳定性、光源功率大小、探测器灵敏度等因素限制。

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    1. 谭智勇,曹俊诚. 太赫兹量子器件光电测试技术与系统. 物理. 2022(05): 328-336 .

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  • Author Information

    • Fu Zhanglong, zlfu@mail.sim.ac.cn On this SiteOn Google Scholar
      • Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
    • Li Ruizhi On this SiteOn Google Scholar
      • Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
      • University of Chinese Academy of Science, Beijing 100049, China
    • Li Hongyi On this SiteOn Google Scholar
      • Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
      • University of Chinese Academy of Science, Beijing 100049, China
    • Qiu Fucheng On this SiteOn Google Scholar
      • Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
      • University of Chinese Academy of Science, Beijing 100049, China
    • Tan Zhiyong On this SiteOn Google Scholar
      • Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
    • Shao Dixiang On this SiteOn Google Scholar
      • Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
      • University of Chinese Academy of Science, Beijing 100049, China
    • Zhang Zhenzhen On this SiteOn Google Scholar
      • Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
    • Gu Liangliang On this SiteOn Google Scholar
      • School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
    • Wan Wenjian On this SiteOn Google Scholar
      • Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
    • Corresponding author: Cao Juncheng, jccao@mail.sim.ac.cn On this SiteOn Google Scholar

      Cao Juncheng, E-mail:jccao@mail.sim.ac.cn

      • Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
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    DOI: 10.12086/oee.2020.190667
    Cite this Article
    Fu Zhanglong, Li Ruizhi, Li Hongyi, Qiu Fucheng, Tan Zhiyong, Shao Dixiang, Zhang Zhenzhen, Gu Liangliang, Wan Wenjian, Cao Juncheng. Research progress of imaging technology based on terahertz quantum well photodetector. Opto-Electronic Engineering 47, 190667 (2020). DOI: 10.12086/oee.2020.190667
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    • Received Date November 01, 2019
    • Revised Date March 11, 2020
    • Published Date April 30, 2020
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  • Detectors NEP/(pW/Hz0.5) Response time/s Frequency/THz
    Golay cell, typical ~140 > 0.03 0.04~20
    VOx bolometers ~40 > 0.01 1.0~10
    LiTiO3 pyroelectric detectors ~400 > 0.01 0.2~30
    Schottky barrier diodes ~100 10-10 0.1~10
    Superconducting hot electron bolometers 0.1 times the quantum limited ~2×10-10 0.1~10
    Si bolometers ~0.1 > 0.025 0.15~20
    Pair-breaking detectors Close to quantum limit ~2×10-10 < 2.0
    Glow discharge detector 12600 ~10-3 0.1~0.25
    Terahertz quantum well photodetector ~0.1 ~10-10 1.5~7.6 & 8.8~20.5
    View in article Downloads
  • Imaging type Frequency /THz Responsivity /(A/W) Detection array size/pixel Resolution/mm Imaging time Signal to noise ratio
    Transmission imaging 3.2 0.5 1 1~1.2 0.5 h 27/17/10
    3.2 0.5 1 0.5 3 h ~100
    Reflection imaging 3.2 0.5 1 ~0.4 1.5 h /
    4.2 0.5 1 0.52 1 h /
    3D imaging 3.2 0.5 1 1(x)/1.2(z) 24 h ~600
    Archimedes spiral scanning imaging 4.2 0.5 1 0.45(x)/0.3(y) 5 s /
    Confocal scanning imaging 4.2 0.5 1 0.11(lateral)/0.32(axial) 5 s ~125
    Pixel-less imaging 5.2 0.22 1 0.05 1 s ~10000
    View in article Downloads

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    Corresponding author: Cao Juncheng, jccao@mail.sim.ac.cn

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    Research progress of imaging technology based on terahertz quantum well photodetector
    • Figure  1

      (a) Device schematic; (b) Band profile of an n-type GaAs/(Al, Ga)As 45° facet coupled THz QWP[10]

    • Figure  2

      (a) Setup of the THz raster scanning transmission imaging system (with a blackbody as the source); (b) Comparison of visible image (top) and THz images for the hidden metal key with different SNR: 27, 17, and 10 (from top to bottom)[40]

    • Figure  3

      (a) Setup of the THz raster scanning transmission imaging system (with a THz QCL as the source); (b), (c) Visible (b) and THz images (c) of the watermark region of a paper money[41]

    • Figure  4

      (a) Setup of the THz raster scanning reflection imaging system (with sample moving); (b), (c) Visible (b) and THz images (c) of the surface of flash disk[42]

    • Figure  5

      (a) Setup of the THz raster scanning reflection imaging system (with mirrors moving); (b), (c) Visible (b) and THz images (c) of a commemorative badge of the 40th anniversary of the University of Chinese Academy of Sciences; (d), (e) Visible (d) and THz images (e) of three drops of water covered with the polyurethane (PU) insulation materials[43]

    • Figure  6

      (a) Setup of the THz 3D imaging system; (b), (c) Visible (b) and THz images (c) of a off-axis parabolic mirror[44]

    • Figure  7

      (a) Setup of the THz archimedes spiral scanning imaging system; (b), (c) Visible (b) and THz images (c) of a leaf half covered with a plastic bag; (d), (e) Visible (d) and THz images (e) of a leaf covered with a polyethylene lid[45]

    • Figure  8

      (a) Setup of the THz confocal scanning imaging system; (b), (c) Visible image (b) of a plastic brush and THz image (c) of it fixed by the tape; (d), (e) Visible (d) and THz images (e) of a razor blade; (f), (g) Visible (f) and THz images (g) of a metal plate; (h), (i) Visible (h) and THz images (i) of a coin[46]

    • Figure  9

      (a) Setup for THz pixelless imaging system; (b) The focal laser spots of the THz QCL imaged by the THz QWP-LED[47]

    • Figure  1
    • Figure  2
    • Figure  3
    • Figure  4
    • Figure  5
    • Figure  6
    • Figure  7
    • Figure  8
    • Figure  9
    Research progress of imaging technology based on terahertz quantum well photodetector
    • Detectors NEP/(pW/Hz0.5) Response time/s Frequency/THz
      Golay cell, typical ~140 > 0.03 0.04~20
      VOx bolometers ~40 > 0.01 1.0~10
      LiTiO3 pyroelectric detectors ~400 > 0.01 0.2~30
      Schottky barrier diodes ~100 10-10 0.1~10
      Superconducting hot electron bolometers 0.1 times the quantum limited ~2×10-10 0.1~10
      Si bolometers ~0.1 > 0.025 0.15~20
      Pair-breaking detectors Close to quantum limit ~2×10-10 < 2.0
      Glow discharge detector 12600 ~10-3 0.1~0.25
      Terahertz quantum well photodetector ~0.1 ~10-10 1.5~7.6 & 8.8~20.5
    • Imaging type Frequency /THz Responsivity /(A/W) Detection array size/pixel Resolution/mm Imaging time Signal to noise ratio
      Transmission imaging 3.2 0.5 1 1~1.2 0.5 h 27/17/10
      3.2 0.5 1 0.5 3 h ~100
      Reflection imaging 3.2 0.5 1 ~0.4 1.5 h /
      4.2 0.5 1 0.52 1 h /
      3D imaging 3.2 0.5 1 1(x)/1.2(z) 24 h ~600
      Archimedes spiral scanning imaging 4.2 0.5 1 0.45(x)/0.3(y) 5 s /
      Confocal scanning imaging 4.2 0.5 1 0.11(lateral)/0.32(axial) 5 s ~125
      Pixel-less imaging 5.2 0.22 1 0.05 1 s ~10000
    • Table  1

      Comparison of main features of common terahertz detectors. Updated with ref.[10]

        1/2
    • Table  2

      Parameters of a imaging system based on THz QWP

        2/2