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摘要: 固态等离激元太赫兹波器件正成为微波毫米波电子器件技术和半导体激光器技术向太赫兹波段发展和融合的重要方向之一。本综述介绍AlGaN/GaN异质结高浓度和高迁移率二维电子气中的等离激元调控、激发及其在太赫兹波探测器、调制器和光源中应用的近期研究进展。通过光栅和太赫兹天线实现自由空间太赫兹波与二维电子气等离激元的耦合，通过太赫兹法布里-珀罗谐振腔进一步调制太赫兹波模式，增强太赫兹波与等离激元的耦合强度。在光栅-谐振腔耦合的二维电子气中验证了场效应栅控的等离激元色散关系，实现了等离激元模式与太赫兹波腔模强耦合产生的等离极化激元模式，演示了太赫兹波的调制和发射。在太赫兹天线耦合二维电子气中实现了等离激元共振与非共振的太赫兹波探测，建立了太赫兹场效应混频探测的物理模型，指导了室温高灵敏度自混频探测器的设计与优化。研究表明，基于非共振等离激元激发可发展形成室温高速高灵敏度的太赫兹探测器及其焦平面阵列技术。然而，固态等离激元的高损耗特性仍是制约基于等离激元共振的高效太赫兹光源和调制器的主要瓶颈。未来的研究重点将围绕高品质因子等离激元谐振腔的构筑，包括固态等离激元物理、等离激元谐振腔边界的调控、新型室温高迁移率二维电子材料的运用和高品质太赫兹谐振腔与等离激元器件的集成等。Abstract: Solid-state terahertz plasma devices are becoming one of the important research areas in which both solid-state microwave/millimeter-wave electronics and semiconductor laser technologies are being developed and merged towards the terahertz frequency regime. In this review, we introduce the manipulation, excitation and probing of two-dimensional-electron-gas (2DEG) plasmons in AlGaN/GaN heterostructure, and report the recent progresses in the implementation of plasmon physics in terahertz detectors, modulators and emitters. The coupling between the plasmon modes and the terahertz electromagnetic waves in free space are realized by using grating coupler, antenna and terahertz Fabry-Pérot cavity which further modulates the terahertz electromagnetic modes and enhances the coupling. The dispersion relationship of gate-controlled plasmon modes are verified in grating-coupled 2DEG. Strong coupling between the plasmon modes and the terahertz cavity modes and hence the formation of plasmon-polariton modes are realized in a grouping-coupled 2DEG embedded in a Fabry-Pérot cavity. Based on the same grating-coupled 2DEG, terahertz modulation with high modulation depth and terahertz plasmon emission are observed. In antenna-coupled 2DEG field-effect channel, both resonant and non-resonant excitation of localized plasmon modes are observed by probing the terahertz photocurrent/voltage. A terahertz self-mixing model is developed for antenna-coupled field-effect terahertz detector and provides a guideline for the design and optimization of high-sensitivity terahertz detectors. Our studies indicate that room-temperature, high-speed and high-sensitivity terahertz detectors and the focal-plane arrays can be developed by using the non-resonant plasmon excitation in antenna-coupled field-effect channel. However, the high damping rate of solid-state plasma wave is yet the main hurdle to overcome for plasmon terahertz emitters and modulators both of which rely on the resonant plasmon excitation. The formation of high-quality-factor plasmon cavity including the solid-state plasma physics, manipulation of the boundary conditions of plasmon cavity, utilization of new high-electron-mobility two-dimensional electronic materials and high-quality, small-mode-volume terahertz resonant cavity, etc. would be the focus of future research.
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Key words:
- two-dimensional electron gas /
- plasmon /
- terahertz /
- gallium nitride
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图 1 AlGaN/GaN异质结的导带能级结构、最低的3个量子阱能级及其电子密度分布的计算结果
Figure 1. Calculated conduction-band diagram of AlGaN/GaN heterostructure, the lowest three quantum states and the electron density distributions
图 2 光栅栅极耦合的AlGaN/GaN二维电子气器件结构
Figure 2. Schematic of grating-coupled two-dimensional electorn gas device
图 3 不同栅压下的光栅耦合二维电子气的太赫兹透射光谱。虚线为法布里-珀罗腔模频率，实线为等离激元模式
Figure 3. Terahertz transmission spectra of the grating-coupled two-dimensional electron gas. Calculated Fabry-Pérot cavity modes and plasmon modes are displayed as the dashed and solid curves, respectively
图 4 仿真得出的法布里-珀罗谐振腔的透射谱
Figure 4. Simulated terahertz transmission spectrum of the Fabry-Pérot cavity
图 5 光栅耦合二维电子气的太赫兹透射光谱的实验结果。虚线和实线分别为等离激元模式和等离极化激元模式的计算结果
Figure 5. Experimental terahertz transmission spectra of a grating-coupled two-dimensional electron gas. The dashed and solid curves are calculated plasmon modes and plasmon-polariton modes, respectively
图 6 (a) 天线耦合的场效应自混频探测器的结构示意图；(b) 栅极电压和源漏电压调控的太赫兹光电流响应的实验结果；(c) 光电流响应的理论计算结果
Figure 6. (a) Schematic of an antenna-coupled field-effect terahertz detector, (b) Measured terahertz photocurrent as a function of the gate voltage and the source-drain bias, (c) Simulated terahertz photocurrent
图 7 (a) 对称天线耦合的场效应自混频探测器。(b) 不同频率太赫兹光照射下太赫兹光电流响应的实验结果和理论计算结果
Figure 7. (a) Field-effect self-mixing terahertz detector with a symmetric antenna, (b) Measured and calculated photocurrent as a function of the gate voltage
图 8 硅透镜、探测器芯片和低噪声放大器集成的太赫兹探测器模组的(a) 侧视图，(b) 背视图和(c) 前视图
Figure 8. Terahertz detector module including a silicon lens, a detector chip and a low-noise amplifier. (a) Full side view, (b) Back view, (c) Front view
图 9 基于0.9 THz太赫兹光源和单像元探测器模块的(a) 透射式扫描成像和(b) 反射式扫描成像
Figure 9. (a) Transmission-type and (b) reflection-type terahertz imaging at 0.9 THz
图 10 (a) 规模为1×16单元线阵列探测器和分立式读出电路组成的线阵列探测器组件。(b) 线阵列探测器组件对0.9 THz聚焦太赫兹光斑的一维扫描成像
Figure 10. (a) A linear detector array (1×16) read out by 16 parallel amplifiers. (b) Intensity profile of a focused 0.9 THz beam imaged by the linear array
图 11 基于AlGaN/GaN场效应自混频探测器的120×120阵列探测器芯片
Figure 11. Terahertz focal-plane array based on 120×120 AlGaN/GaN self-mixing field-effect transistors
图 12 频率为1.06 THz的载波透射系数随栅压的变化以及器件动态工作时所加调制栅压和受调制太赫兹信号示意图
Figure 12. Terahertz transmission characteristic at a carrier frequency of 1.06 THz as function of gate voltage and the schematic of the dynamic operation
图 13 频率为0.67 THz、0.85 THz和1.27 THz的腔模透射系数随栅压的变化。图中标出了器件直流工作点和调制深度
Figure 13. Transmission characteristics at different gate voltages in cavity mode 0.67 THz, 0.85 THz and 1.27 THz
图 14 调制器在不同栅压下的透射谱
Figure 14. Transmission spectrum of the modulator at different gate voltages
图 15 在频率为0.436 THz的载波下测试调制器的静态特性，图中标出了调制深度
Figure 15. Static characteristics of the modulator at 0.436 THz, and the modulation depth is demonstrated
图 16 集成了F-P谐振腔的等离激元太赫兹源的结构示意图
Figure 16. Schematic cross section of plasmon terahertz emitter embedded in a F-P cavity
图 17 (a) 光源器件在VG=-1 V时的干涉图；(b) 发射光谱
Figure 17. (a) Interferogram of the device under gate voltage of -1 V, (b) Emission spectrum obtained through FFT
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[1] RADISIC V, LEONG K M K H, MEI X, et al.. Power amplification at 0.65 THz Using InP HEMTs[J]. IEEE Transactions on Microwave Theory and Techniques, 2012, 60(3):724-729. doi: 10.1109/TMTT.2011.2176503 [2] LEONG K M K H, MEI X, YOSHIDA W, et al.. A 0.85 THz low noise amplifier using InP HEMT transistors[J]. IEEE Microwave and Wireless Components Letters, 2015, 25(6):397-399. doi: 10.1109/LMWC.2015.2421336 [3] KOHLER R, TREDICUCCI A, BELTRAM F, et al.. Terahertz semiconductor-heterostructure laser[J]. Nature, 2002, 417(6885):156-159. doi: 10.1038/417156a [4] WILLIAMS B S, KUMAR S, HU Q, et al.. High-power terahertz quantum-cascade lasers[J]. Electronics Letters, 2006, 42(2):89-91. doi: 10.1049/el:20063921 [5] LI L H, CHEN L, ZHU J X, et al.. Terahertz quantum cascade lasers with >1 W output powers[J]. Electronics Letters, 2014, 50(4):309-310. doi: 10.1049/el.2013.4035 [6] ALLEN S J, TSUI D C, LOGAN R A. Observation of the two-dimensional plasmon in silicon inversion layers[J]. Physical Review Letters, 1977, 38(17):980-983. doi: 10.1103/PhysRevLett.38.980 [7] GORNIK E, TSUI D C. Voltage-tunable far-infrared emission from Si inversion layers[J]. Physical Review Letters, 1976, 37(21):1425-1428. doi: 10.1103/PhysRevLett.37.1425 [8] HÖPFEL R A, VASS E, GORNIK E. Thermal excitation of two-dimensional plasma oscillations[J]. Physical Review Letters, 1982, 49(22):1667-1671. doi: 10.1103/PhysRevLett.49.1667 [9] HIRAKAWA K, YAMANAKA K, GRAYSON M, et al.. Far-infrared emission-spectroscopy of hot 2-dimensional plasmons in Al0.3Ga0.7As/GaAs heterojunctions[J]. Applied Physics Letters, 1995, 67(16):2326-2328. doi: 10.1063/1.114333 [10] KEMPA K, BAKSHI P, XIE H, et al.. Current-driven plasma instabilities in solid-state layered systems with a grating[J]. Physical Review B, 1993, 47(8):4532-4536. doi: 10.1103/PhysRevB.47.4532 [11] MIKHAILOV S A. Plasma instability and amplification of electromagnetic waves in low-dimensional electron systems[J]. Physical Review B, 1998, 58(3):1517-1532. doi: 10.1103/PhysRevB.58.1517 [12] DYAKONOV M, SHUR M. Shallow-water analogy for a ballistic field-effect transistor:new mechanism of plasma-wave generation by Dc current[J]. Physical Review Letters, 1993, 71(15):2465-2468. doi: 10.1103/PhysRevLett.71.2465 [13] BOUBANGA-TOMBET S, TEPPE F, TORRES J, et al.. Room temperature coherent and voltage tunable terahertz emission from nanometer-sized field effect transistors[J]. Applied Physics Letters, 2010, 97(26):262108. doi: 10.1063/1.3529464 [14] LISAUSKAS A, PFEIFFER U, OJEFORS E, et al.. Rational design of high-responsivity detectors of terahertz radiation based on distributed self-mixing in silicon field-effect transistors[J]. J. Applied Physics, 2009, 105(11):114511. doi: 10.1063/1.3140611 [15] KNAP W, DENG Y, RUMYANTSEV S, et al.. Resonant detection of subterahertz radiation by plasma waves in a submicron field-effect transistor[J]. Applied Physics Letters, 2002, 80(18):3433-3435. doi: 10.1063/1.1473685 [16] KNAP W, KACHOROVSKⅡ V, DENG Y, et al. Nonresonant detection of terahertz radiation in field effect transistors[J]. J. Applied Physics, 2002, 91(11):9346-9353. doi: 10.1063/1.1468257 [17] DYAKONOV M I, SHUR M S. Plasma wave electronics:novel terahertz devices using two dimensional electron fluid[J]. IEEE Transactions on Electron Devices, 1996, 43(10):1640-1645. doi: 10.1109/16.536809 [18] ELKHATIB T A, KACHOROVSKⅡ V Y, STILLMAN W J, et al. Terahertz response of field-effect transistors in saturation regime[J]. Applied Physics Letters, 2011, 98(24):243505. doi: 10.1063/1.3584137 [19] GUTIN A, KACHOROVSKⅡ V, MURAVIEV A, et al.. Plasmonic terahertz detector response at high intensities[J]. J. Applied Physics, 2012, 112(1):014508. doi: 10.1063/1.4732138 [20] KNAP W, DYAKONOV M, COQUILLAT D, et al.. Field effect transistors for terahertz detection:physics and first imaging applications[J]. J. Infrared Millimeter and Terahertz Waves, 2009, 30(12):1319-1337. [21] KACHOROVSKⅡ V Y, RUMYANTSEV S L, KNAP W, et al.. Performance limits for field effect transistors as terahertz detectors[J]. Applied Physics Letters, 2013, 102(22):223505. doi: 10.1063/1.4809672 [22] SHUR M. Terahertz electronics for sensing applications[C]. Sensors, IEEE, Limerick, Ireland, 2011:40-43. [23] PREU S, LU H, SHERWINM S, et al.. Detection of nanosecond-scale, high power THz pulses with a field effect transistor[J]. Review of Scientific Instruments, 2012, 83(5):053101. doi: 10.1063/1.4705986 [24] BUT D B, DREXLER C, SAKHNO M V, et al.. Nonlinear photoresponse of field effect transistors terahertz detectors at high irradiation intensities[J]. J. Applied Physics, 2014, 115(16):164514. doi: 10.1063/1.4872031 [25] DYAKONOVA N, BUT D B, COQUILLAT D, et al.. AlGaN/GaN HEMT's photoresponse to high intensity THz radiation[J]. Opto-Electronics Review, 2015, 23(3):195-199. [26] STILLMAN W J, SHUR M S. Closing the gap:plasma wave electronic terahertz detectors[J]. J. Nanoelectronics and Optoelectronics, 2007, 2(3):209-221. doi: 10.1166/jno.2007.301 [27] LU J Q, SHUR M S, HESLER J L, et al.. Terahertz detector utilizing two-dimensional electronic fluid[J]. IEEE Electron Device Letters, 1998, 19(10):373-375. doi: 10.1109/55.720190 [28] WEIKLE R, LU J Q, SHUR M S, et al.. Detection of microwave radiation by electronic fluid in high electron mobility transistors[J]. Electronics Letters, 1996, 32(23):2148-2149. doi: 10.1049/el:19961410 [29] KNAP W, DENG Y, RUMYANTSEV S, et al.. Resonant detection of subterahertz and terahertz radiation by plasma waves in submicron field-effect transistors[J]. Applied Physics Letters, 2002, 81(24):4637-4639. doi: 10.1063/1.1525851 [30] KANG S, BURKE P J, PFEIFFER L N, et al.. Resonant frequency response of plasma wave detectors[J]. Applied Physics Letters, 2006, 89(21):213512. doi: 10.1063/1.2393023 [31] EL FATIMY A, TEPPE F, DYAKONOVA N, et al.. Resonant and voltage-tunable terahertz detection in InGaAs/InP nanometer transistors[J]. Applied Physics Letters, 2006, 89(13):131926. doi: 10.1063/1.2358816 [32] PERALTA X G, ALLEN S J, WANKE M C, et al.. Terahertz photoconductivity and plasmon modes in double-quantum-well field-effect transistors[J]. Applied Physics Letters, 2002, 81(9):1627-1629. doi: 10.1063/1.1497433 [33] EL FATIMY A, TOMBET S B, TEPPE F, et al.. Terahertz detection by GaN/AlGaN transistors[J]. Electronics Letters, 2006, 42(23):1342-1344. doi: 10.1049/el:20062452 [34] GOLENKOV A. Sub-THz nonresonant detection in AlGaN/GaN heterojunction FETs[J]. Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015, 18(1):40-45. [35] LISAUSKAS A, BOPPEL S, SELIUTA D, et al.. Terahertz detection and coherent imaging from 0.2 to 4.3 THz with silicon CMOS field-effect transistors[C]. Microwave Symposium Digest (MTT), IEEE MTT-S International, Montreal, Canada, 2012:1-3. [36] BOPPEL S, LISAUSKAS A, MAX A, et al.. CMOS detector arrays in a virtual 10-kilopixel camera for coherent terahertz real-time imaging[J]. Optics Letters, 2012, 37(4):536-538. doi: 10.1364/OL.37.000536 [37] BOPPEL S, LISAUSKAS A, MUNDT M, et al.. CMOS integrated antenna-coupled field-effect transistors for the detection of radiation from 0.2 to 4.3 THz[J]. IEEE Transactions on Microwave Theory and Techniques, 2012, 60(12):3834-3843. doi: 10.1109/TMTT.2012.2221732 [38] PERENZONI D, PERENZONI M, GONZO L, et al.. Analysis and design of a CMOS-based terahertz sensor and readout[C]. Proceedings of SPIE, Optical Sensing and Detection, Brussels, Belgium, 2010, 7726:772618. [39] BAUER M, VENCKEVICIUS R, KASALYNAS I, et al.. Antenna-coupled field-effect transistors for multi-spectral terahertz imaging up to 4.25 THz[J]. Optics Express, 2014, 22(16):19250-19256. [40] AL HADI R, SHERRY H, GRZYB J, et al.. A 1 k-Pixel Video Camera for 0.7-1.1 Terahertz Imaging Applications in 65-nm CMOS[J]. IEEE Journal of Solid-State Circuits, 2012, 47(12):2999-3012. doi: 10.1109/JSSC.2012.2217851 [41] SHERRY H, AL HADI R, GRZYB J, et al.. Lens-integrated THz imaging arrays in 65nm CMOS technologies[C]. Radio Frequency Integrated Circuits Symposium (RFIC), IEEE, Baltimore, MD, USA, 2011:1-4. [42] TOMADIN A, TREDICUCCI A, PELLEGRINI V, et al.. Photocurrent-based detection of terahertz radiation in graphene[J]. Applied Physics Letters, 2013, 103(21):211120. doi: 10.1063/1.4831682 [43] OTSUJI T, TOMBET S A B, SATOU A, et al.. Graphene-based devices in terahertz science and technology[J]. J. Physics D:Applied Physics, 2012, 45(30):303001. doi: 10.1088/0022-3727/45/30/303001 [44] VICARELLI L, VITIELLO M S, COQUILLAT D, et al.. Graphene field-effect transistors as room-temperature terahertz detectors[J]. Nature Materials, 2012, 11(10):865-871. doi: 10.1038/nmat3417 [45] YANG X X, SUN J D, QIN H, et al.. Room-temperature terahertz detection based on CVD graphene transistor[J]. Chinese Physics B, 2015, 24(4):047206. doi: 10.1088/1674-1056/24/4/047206 [46] ZAK A, ANDERSSON M A, BAUER M, et al.. Antenna-integrated 0.6 THz FET direct detectors based on CVD graphene[J]. Nano Letters, 2014, 14(10):5834-5838. doi: 10.1021/nl5027309 [47] NAKAMURA S, MUKAI T, SENOH M. High-brightness InGaN/AlGaN double-heterostructure blue-green-light-emitting diodes[J]. J. Applied Physics, 1994, 76(12):8189-8191. doi: 10.1063/1.357872 [48] NAKAMURA S, SENOH N, IWASA N, et al.. High-brightness InGaN blue, green and yellow light-emitting diodes with quantum well structures[J]. Japanese J. Applied Physics, 1995, 34(7A):L797-L799. [49] AMBACHER O. Growth and applications of Group Ⅲ-nitrides[J]. J. Physics D:Applied Physics, 1998, 31(20):2653-2710. doi: 10.1088/0022-3727/31/20/001 [50] QIN H, YU Y, LI X, et al.. Excitation of terahertz plasmon in two-dimensional electron gas[J]. Terahertz Science and Technology, 2016, 9(2):71-81. [51] TAN R B.Theoretical study on two-dimensional electron gas based terahertz device[D]. Beijing:University of Chinese Academy of Sciences 2013.(in Chinese) [52] STERN F. Polarizability of a two-dimensional electron gas[J]. Physical Review Letters, 1967, 18(14):546-548. doi: 10.1103/PhysRevLett.18.546 [53] CHAPLIK A V. Possible crystallization of charge carriers in low-density inversion layers[J]. Soviet J. Experimental and Theoretical Physics, 1972, 35(2):395-398. [54] SHUR M. Plasma wave terahertz electronics[J]. Electronics Letters, 2010, 46(26):S18-S21. doi: 10.1049/el.2010.8457 [55] SHANER E A, GRINE A D, WANKE M C, et al.. Far-infrared spectrum analysis using plasmon modes in a quantum-well transistor[J]. IEEE Photonics Technology Letters, 2006, 18(17-20):1925-1927. [56] SUN J D, SUN Y F, WU D M, et al. High-responsivity, low-noise, room-temperature, self-mixing terahertz detector realized using floating antennas on a GaN-based field-effect transistor[J]. Applied Physics Letters, 2012, 100(1):013506. doi: 10.1063/1.3673617 [57] DYER G C, VINH N Q, ALLEN S J, et al.. A terahertz plasmon cavity detector[J]. Applied Physics Letters, 2010, 97(19):193507. doi: 10.1063/1.3513339 [58] AIZIN G R, DYER G C. Transmission line theory of collective plasma excitations in periodic two-dimensional electron systems:Finite plasmonic crystals and Tamm states[J]. Physical Review B, 2012, 86(23):235316. doi: 10.1103/PhysRevB.86.235316 [59] HUANG Y D.Manipulation of the interaction between two-dimensional plasma waves and terahertz electromagnetic waves[D]. Beijing:University of Chinese Academy of Sciences, 2013.(in Chinese) [60] SUN J D, QIN H, LEWIS R A, et al. Probing and modelling the localized self-mixing in a GaN/AlGaN field-effect terahertz detector[J]. Applied Physics Letters, 2012, 100(17):173513. doi: 10.1063/1.4705306 [61] SUN J D, QIN H, LEWIS R A, et al.. The effect of symmetry on resonant and nonresonant photoresponses in a field-effect terahertz detector[J]. Applied Physics Letters, 2015, 106(3):031119. doi: 10.1063/1.4906536 [62] TEPPE F, KNAP W, VEKSLER D, et al.. Room-temperature plasma waves resonant detection of sub-terahertz radiation by nanometer field-effect transistor[J]. Applied Physics Letters, 2005, 87(5):052107. doi: 10.1063/1.2005394 [63] TEPPE F, VEKSLER D, KACHOROVSKI V Y, et al. Plasma wave resonant detection of femtosecond pulsed terahertz radiation by a nanometer field-effect transistor[J]. Applied Physics Letters, 2005, 87(2):022102. doi: 10.1063/1.1952578 [64] SUN Y F, SUN J D, ZHOU Y, et al.. Room temperature GaN/AlGaN self-mixing terahertz detector enhanced by resonant antennas[J]. Applied Physics Letters, 2011, 98(25):252103. doi: 10.1063/1.3601489 [65] LIU L, HESLER J L, XU H Y, et al.. A broadband quasi-optical terahertz detector utilizing a zero bias schottky diode[J]. IEEE Microwave and Wireless Components Letters, 2010, 20(9):504-506. doi: 10.1109/LMWC.2010.2055553 [66] SEMENOV A D, RICHTER H, HUBERS H W, et al. Terahertz performance of integrated lens antennas with a hot-electron bolometer[J]. IEEE Transactions on Microwave Theory and Techniques, 2007, 55(2):239-247. doi: 10.1109/TMTT.2006.889153 [67] DYER G C, PREU S, AIZIN G R, et al.. Enhanced performance of resonant sub-terahertz detection in a plasmonic cavity[J]. Applied Physics Letters, 2012, 100(8):083506. doi: 10.1063/1.3687698 [68] 李琦, 胡佳琦, 杨永发.太赫兹Gabor同轴数字全息二维再现像复原[J].光学精密工程, 2014, 22(8):2188-2195. doi: 10.3788/OPE.LI Q, HU J Q, YANG Y F. 2D reconstructed-image restoration of terahertz Gabor in-line digital holography[J]. Opt. Precision Eng., 2014, 22(8):2188-2195.(in Chinese) doi: 10.3788/OPE. [69] 田莉, 金伟其, 蔡毅, 等.THz焦平面连续波透射成像系统的成像面积及对比度[J].光学精密工程, 2015, 23(8):2164-2170. doi: 10.3788/OPE.TIAN L, JIN W Q, CAI Y, et al.. Imaging area and contrast of THz focal plan array CW transmission imaging system[J]. Opt. Precision Eng., 2015, 23(8):2164-2170.(in Chinese) doi: 10.3788/OPE. -
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