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Holography in the invisible. From the thermal infrared to the terahertz waves: outstanding applications and fundamental limits

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Light(Advanced Manufacturing) 2022年第2期3卷 157-170页

作者： Marc Georges Yuchen Zhao Jean-François Vandenrijt Centre Spatial de Liège STAR Research InstituteLiège UniversitéLiege Science Park4031 Angleur(Liège)Belgium

Since its invention,holography has been mostly applied at visible wavelengths in a variety of applications.Specifically,non-destructive testing of manufactured objects was a driver for developing holographic methods and all related ones based on the speckle pattern recording.One substantial limitation of holographic non-destructive testing is the setup stability requirements directly related to the laser wavelength.This observation has driven some works for 15 years:developing holography at wavelengths much longer than visible ones.In this paper,we will first review researches carried out in the infrared,mostly digital holography at thermal infrared wavelengths around 10 micrometers.We will discuss the advantages of using such wavelengths and show different examples of applications.In nondestructive testing,large wavelengths allow using digital holography in perturbed environments on large objects and measure large deformations,typical of the aerospace domain.Other astonishing applications such as reconstructing scenes through smoke and flames were proposed.When moving further in the spectrum,digital holography with so-called terahertz waves(up to 3 millimeters wavelength)has also been studied.The main advantage here is that these waves easily penetrate some materials.Therefore,one can envisage terahertz digital holography to reconstruct the amplitude and phase of visually opaque objects.We review some cases in which terahertz digital holography has shown potential in biomedical and industrial applications.We will also address some fundamental bottlenecks that prevent fully benefiting from the advantages of digital holography when increasing the wavelength.

关键词： Long wave infrared terahertz waves Digital holography Speckle interferometry

Generation and detection of pulsed terahertz waves in gas： from elongated plasmas to microplasmas

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Frontiers of Optoelectronics 2018年第3期11卷 209-244页

作者： Fabrizio BUCCHERI Pingjie HUANG Xi-Cheng ZHANG The Institute of Optics University of Rochester Rochester NY 14627 USA State Key Laboratory of IndustrialControl Technology College of Control Science and Engineering Zhejiang University Hangzhou 310027 China The Beijing Advanced Innovation Center for Imaging Technology Capital Normal University Beijing 100037 China

The past two decades have seen an exponential growth of interest in one of the least explored region of the electromagnetic spectrum, the terahertz （THz） frequency band, ranging from to 0.1 to 10 THz. Once only the realm of astrophysicists studying the background radiation of the universe, THz waves have become little by little relevant in the most diverse fields, such as medical imaging, industrial inspection, remote sensing, fundamental science, and so on. Remarkably, THz wave radiation can be generated and detected by using ambient air as the source and the sensor. This is accomplished by creating plasma under the illumination of intense femtosecond laser fields. The integration of such a plasma source and sensor in THz time-domain techniques allows spectral measurements covering the whole THz gap （0.1 to 10 THz）, further increasing the impact of this scientific tool in the study of the four states of matter. In this review, the authors introduce a new paradigm for implementing THz plasma techniques. Specifically, we replaced the use of elongated plasmas, ranging from few mm to several cm, with sub-mm plasmas, which will be referred to as microplasmas, obtained by focusing ultrafast laser pulses with high numerical aperture optics （NA from 0.1 to 0.9）. The experimental study of the THz emission and detection from laser-induced plasmas of submillimeter size are presented. Regarding the microplasma source, one of the interesting phenomena is that the main direction of THz wave emission is almost orthogonal to the laser propagation direction, unlike that of elongated plasmas. Perhaps the most important achievement is the demonstra- tion that laser pulse energies lower than 1 μJ are sufficientto generate measurable THz pulses from ambient air, thus reducing the required laser energy requirement of two orders of magnitude compared to the state of art. This significant decrease in the required laser energy will make plasma-based THz techniques more accessible to the scientific community, as well as opening new pot

关键词： terahertz waves terahertz Air Photonics generation and detection elongated plasmas microplasmas

Anisotropic coding metamaterials and their powerful manipulation of differently polarized terahertz waves

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Light(Science & Applications) 2016年第1期5卷 767-777页

作者： Shuo Liu Tie Jun Cui Quan Xu Di Bao Liangliang Du Xiang Wan Wen Xuan Tang Chunmei Ouyang Xiao Yang Zhou Hao Yuan Hui Feng Ma Wei Xiang Jiang Jiaguang Han Weili Zhang Qiang Cheng State Key Laboratory of Millimeter waves Southeast UniversityNanjing 210096China Synergetic Innovation Center of Wireless Communication Technology Southeast UniversityNanjing 210096China Cooperative Innovation Centre of terahertz Science Chengdu 610054China Center for terahertz waves and College of Precision Instrument and Optoelectronics Engineering Tianjin UniversityTianjin 300072China Jiangsu Xuantu Technology Co. Ltd.Nanjing 211111China

Metamaterials based on effective media can be used to produce a number of unusual physical properties(for example,negative refraction and invisibility cloaking)because they can be tailored with effective medium parameters that do not occur in nature.Recently,the use of coding metamaterials has been suggested for the control of electromagnetic waves through the design of coding sequences using digital elements‘0’and‘1,'which possess opposite phase responses.Here we propose the concept of an anisotropic coding metamaterial in which the coding behaviors in different directions are dependent on the polarization status of the electromagnetic waves.We experimentally demonstrate an ultrathin and flexible polarization-controlled anisotropic coding metasurface that functions in the terahertz regime using specially designed coding elements.By encoding the elements with elaborately designed coding sequences(both 1-bit and 2-bit sequences),the x-and y-polarized waves can be anomalously reflected or independently diffused in three dimensions.The simulated far-field scattering patterns and near-field distributions are presented to illustrate the dual-functional performance of the encoded metasurface,and the results are consistent with the measured results.We further demonstrate the ability of the anisotropic coding metasurfaces to generate a beam splitter and realize simultaneous anomalous reflections and polarization conversions,thus providing powerful control of differently polarized electromagnetic waves.The proposed method enables versatile beam behaviors under orthogonal polarizations using a single metasurface and has the potential for use in the development of interesting terahertz devices.

关键词： anisotropic metamaterial design coding metamaterial metasurface terahertz waves

terahertz electromagnetic waves emitted from semiconductor investigated using terahertz time domain spectroscopy

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Chinese Optics Letters 2011年第11期9卷 33-39页

作者：朱亦鸣庄松林 Engineering Research Center of Optical Instrument and System Ministry of EducationShanghai Key Lab of Modern Optical SystemUniversity of Shanghai for Science and Technology School of Microelectronics Shanghai Jiao Tong University

Ultrafast electromagnetic waves radiated from semiconductor material under high electric fields and photoexcited by femtosecond laser pulses have been recorded by using terahertz time domain spectroscopy （THz-TDS）.The waveforms of these electromagnetic waves reflect the dynamics of the photoexcited carriers in the semiconductor material,thus,THz-TDS provides a unique opportunity to observe directly the temporal and spatial evolutions of non-equilibrium transport of carriers within sub-picosecond time scale.We report on the observed THz emission waveforms emitted from GaAs by using a novel technology,the time domain THz electro-optic （EO） sampling,which has a bipolar feature,i.e.,an initial positive peak and a subsequent negative dip that arises from its velocity overshoot.The initial positive peak has been interpreted as electron acceleration in the bottom of Γ valley in GaAs,where electrons have a light effective mass.The subsequent negative dip has been attributed to intervalley transfer from Γ to X and L valleys.Furthermore,the power dissipation spectra of the bulk GaAs in THz range are also investigated by using the Fourier transformation of the time domain THz traces.From the power dissipation spectra,the cutoff frequency for negative power dissipation （i.e.,gain） under step electric field in the bulk GaAs can also be obtained.The cutoff frequency for the gain gradually increases with increasing electric fields up to 50 kV/cm and achieves saturation at approximately 1 THz at 300 K.Furthermore,based on the temperature dependence of the cutoff frequency,we find that this cutoff frequency is governed by the energy relaxation process of electrons from L to Γ valley via successive optical phonon emission.

关键词： Cutoff frequency Electric fields Electric losses Electromagnetic waves Electromagnetism Fourier analysis Fourier transforms Gallium arsenide Landforms Magnetic materials Semiconducting gallium terahertz waves Ultrafast lasers Ultrashort pulses

Broadband diffusion of terahertz waves by multi-bit coding metasurfaces

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Light(Science & Applications) 2015年第1期4卷 207-215页

作者： Li-Hua Gao Qiang Cheng Jing Yang Shao-Jie Ma Jie Zhao Shuo Liu Hai-Bing Chen Qiong He Wei-Xiang Jiang Hui-Feng Ma Qi-Ye Wen Lan-Ju Liang Biao-Bing Jin Wei-Wei Liu Lei Zhou Jian-Quan Yao Pei-Heng Wu Tie-Jun Cui State Key Laboratory of Millimeter waves Department of Radio EngineeringSoutheast UniversityNanjing 210096China Cooperative Innovation Centre of terahertz Science No.4Section 2North Jianshe RoadChengdu 610054China Institute of Modern Optics Key Laboratory of Optical Information Science and Technology(Ministry of Education)Nankai UniversityTianjin 300071China State Key Laboratory of Surface Physics Key Laboratory of Micro and Nano Photonic Structures(Ministry of Education)Department of PhysicsFudan UniversityShanghai 200433China State Key Laboratory of Electronic Films and Integrated Devices University of Electronic Science and TechnologyChengdu 610054China Research Institute of Superconductor Electronics(RISE) School of Electronic Science and EngineeringNanjing UniversityNanjing 210093China Institute of Lasers and Optoelectronics College of Precision Instrument and Opto-Electronics EngineeringTianjin UniversityTianjin 300072China

The terahertz region is a special region of the electromagnetic spectrum that incorporates the advantages of both microwaves and infrared light waves.In the past decade,metamaterials with effective medium parameters or gradient phases have been studied to control terahertz waves and realize functional devices.Here,we present a new approach to manipulate terahertz waves by using coding metasurfaces that are composed of digital coding elements.We propose a general coding unit based on a Minkowski closed-loop particle that is capable of generating 1-bit coding(with two phase states of 0 and 180°),2-bit coding(with four phase states of 0,90°,180°,and 270°),and multi-bit coding elements in the terahertz frequencies by using different geometric scales.We show that multi-bit coding metasurfaces have strong abilities to control terahertz waves by designing-specific coding sequences.As an application,we demonstrate a new scattering strategy of terahertz waves—broadband and wide-angle diffusion—using a 2-bit coding metasurface with a special coding design and verify it by both numerical simulations and experiments.The presented method opens a new route to reducing the scattering of terahertz waves.

关键词： coding diffusion metasurface terahertz waves

Difference analysis in terahertz wave propagation in thermochemical nonequilibrium plasma sheath under different hypersonic vehicle shapes

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Chinese Journal of Aeronautics 2023年第10期36卷 137-151页

作者： Wenchong OUYANG Qi LIU Zhengwei WU School of Nuclear Science and Technology University of Science and Technology of ChinaHefei 230026China Joint Laboratory of Plasma Application Technology Institute of Advanced TechnologyUniversity of Science and Technology of ChinaHefei 230031China CAS Key Laboratory of Geospace Environment University of Science and Technology of ChinaHefei 230026China

Research on terahertz communication under different vehicles has important guiding significance for the design of future hypersonic vehicle and Radio Frequency(RF)blackout.In this paper,a joint simulation model of plasma flow under thermochemical nonequilibrium state and terahertz transmission is developed to investigate the differences in terahertz wave transmission characteristics under different vehicle shapes and the related mechanisms.By comparing the plasma sheath characteristics and terahertz transmission among HIFIRE-5b(Hypersonic International Flight Research Experimentation-5b),RAM C(Radio Attenuation Measurement C)and ARD(Atmospheric Reentry Demonstrator)vehicles,it is found that the sheath thickness and electron density of ARD vehicles is significantly larger than that of HIFIRE-5b and RAM C vehicles,resulting in greater terahertz wave attenuation.Collision absorption plays a major role in the terahertz attenuation of vehicles,and the contribution of reflection effects is only observed in the ARD vehicle due to its larger plasma sheath thickness and spatial structure variation.Based on the above comparison results,a shape design scheme of reducing the vehicle head and tail for mitigating RF blackout is proposed,and the scheme is proved by further analyzing the effects of different vehicle heads and tails on the terahertz communication.With the decrease of the head radius and tail width of hypersonic vehicle,the wave attenuation at the same terahertz frequency decreases,and the contribution of reflection effect to wave attenuation gradually disappears.Therefore,the shape design scheme of reducing the vehicle head and tail can effectively alleviate the RF blackout problem,which provides an important reference value for future hypersonic vehicle design.

关键词： Hypersonic vehicles Plasma flow Plasma sheaths Shape optimization terahertz waves Wave propagation

Cell-type continuous electromagnetic radiation system generating millimeter waves for active denial system applications

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Defence Technology（防务技术） 2022年第10期18卷 1895-1913页

作者： Sun-Hong Min Ohjoon Kwon Matlabjon Sattorov Seontae Kim In-Keun Baek Seunghyuk Park Ranjan Kumar Barik Anirban Bera Dongpyo Hong Seonmyeong Kim Bong Hwan Hong Chawon Park Sukhwal Ma Minho Kim Kyo Chul Lee Yong Jin Lee Han Byul Kwon Young Joon Yoo Sang Yoon Park Gun-Sik Park Korea Institute of Radiological and Medical Sciences(KIRAMS) Seoul01812South Korea Institute for Basic Science Center for Axion and Precision Physics ResearchDaejeon34141South Korea Center for THz-Driven Biomedical Systems Department of Physics and AstronomyCollege of Natural SciencesSeoul National UniversitySeoul08826South Korea Center for Applied Electromagnetic Research Advanced Institute of Convergence TechnologySuwonGyeonggi-do16229South Korea R&D Department Seoul-TeracomInc.Suwon16229South Korea Mechatronics R&D Center Samsung Electronics Co.Ltd.Hwasung18448South Korea Hanwha Corporation Gumi730-030South Korea Council of Scientific and Industrial Research Central Electronics Engineering Research InstitutePilani333031India Home Economics Education/Biosystems and Biomedical Sciences Korea UniversitySeoul02841South Korea Current affiliation of Seontae Kim:Young IN ACE 1 F60Anyangcheondong-roDongan-guAnyang-siGyeonggi-do14042South Korea.

The cell-type continuous electromagnetic radiation system is a demonstration device capable of generating high-power millimeter electromagnetic waves of a specific wavelength and observing their effects on living organisms.It irradiates a biological sample placed in a 30×30×50 cm^(3)cell with electromagnetic waves in the 3.15-mm-wavelength region(with an output of≥1 W)and analyzes the temperature change of the sample.A vacuum electronic device-based coupled-cavity backward-wave oscillator converts the electron energy of the electron beam into radiofrequency(RF)energy and radiates it to the target through an antenna,increasing the temperature through the absorption of RF energy in the skin.The system causes pain and ultimately reduces combat power.A cell-type continuous electromagnetic radiation system consisting of four parts—an electromagnetic-wave generator,a highvoltage power supply,a test cell,and a system controller—generates an RF signal of≥1 W in a continuous waveform at a 95-GHz center frequency,as well as a chemical solution with a dielectric constant similar to that of the skin of a living organism.An increase of 5°C lasting approximately 10 s was confirmed through an experiment.

关键词： Millimeter waves terahertz waves Coupled-cavity backward wave oscillator(CCBWO) Cell-type continuous electromagnetic radiation Active denial system(ADS) Directed-energy weapon(DEW)

Frequency spectrum characterization of terahertz emission from laser-induced air plasma

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Chinese Optics Letters 2014年第8期12卷 96-98页

作者：赵骥张亮亮骆怡蔓吴同张存林赵跃进 Beijing Key Laboratory for Precision Optoelectronic Measurement Instrument and Technology School of Optoelectronics Beijing Institute of Technology Beijing Key Laboratory for terahertz Spectroscopy and Imaging Key Laboratory of Terahertz OptoelectronicsMinistry of EducationCapital Normal University

terahertz （THz） emission from laser-induced air-plasma is presented. The frequency spectra of THz wave are investigated using an air-biased-coherent-detection method. The frequency spectra are measured under different pump-pulse and probe-pulse energies. The frequency pump power and we speculate it caused by collision behavior spectra become narrow with the increasing Meanwhile, the bandwidth of the frequency spectra is broadened by the increasing probe power, which can be explained by pulse compression. Based on this finding, the optimal frequency spectrum of THz can be achieved by regulating the probe and pump beam.

关键词： Bandwidth compression Laser produced plasmas Optical pumping Probes Spectroscopy terahertz waves

Single-shot measurement of THz pulses

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Chinese Physics B 2020年第5期29卷 37-40页

作者：杨磊侯磊董陈岗施卫 Key Laboratory of Ultrafast Photoelectric Technology and terahertz Science in Shaanxi Xi’an University of TechnologyXi’an 710048China

terahertz(THz) waves have shown a broad prospect in the analysis of some dielectric materials because of their special properties. For the ultrafast irreversible processes, the THz single-shot measurement is a good choice. In this paper,a single-shot system is investigated, where a pump beam is used to generate THz pulses with high electrical field by optical rectification in LiNbO3, the probe beam with wavefront tilted by a blazed grating is used for single-shot measurement. The time window is up to 90 ps, the signal to noise ratio is 2000 : 1, the spectrum covers from 0.1 THz to about 2.0 THz, and the spectral resolution is 0.011 THz. The single-shot measurement result agrees well with that of a traditional electrical-optic sampling method.

关键词： terahertz waves tilted wavefront single-shot measurement