A life with terahertz waves

A fascination with electromagnetic waves at the boundary between light and radio waves

A prototype of the integrated terahertz radar. © Yasuaki Monnai, Keio University

https://research-highlights.keio.ac.jp/2020/07/a.html?fbclid=IwAR2B9o9ScG8k6U-Lpjdw98NcQZ8-hZ91KjYQ48WQ9-pC5LgMrQfiDle7OOA

First encounters with terahertz waves

"My doctoral research was on controlling beams of terahertz radiation," says Yasuaki Monnai, an associate professor at Keio University's Department of Applied Physics and Physico-Informatics. "We were working at the boundary between light and radio waves. Most likely, what led me to follow this path was meeting a professor who was transmitting electric power wirelessly using microwaves. I was impressed by his ideas and methodology, which eventually led to my interest in terahertz waves, waves that have higher frequencies than microwaves."

Monnai adds that research on light and radio waves evolved as separate fields, with few technological advances at the boundaries of these waves. Furthermore, radio waves are generated by oscillator circuits and transmitted using antennae, but light is generated by lasers and transmitted using lens systems.

Although the terahertz frequency band has the potential for communication speeds much higher than the best of today's Wi-Fi, enabling instant downloads of high-definition images, one of the issues to overcome is preventing the divergence of terahertz beams. "For example, infrared remote TV-controllers are highly directional and if they are pointed slightly away from the target, they fail to work," explains Monnai. "For my doctorate, I proposed a device to control the directionality of terahertz beams and demonstrated its principle of action. I had to visit a group in Germany to complete my research because my laboratory in Japan did not have the highly specialized terahertz wave equipment required."

Studying in Germany and the verbalization of ideas

Monnai's memories of his stay in Germany include how students approached their research and job hunting. "In Japan, it is assumed that all students work along the same timeline towards important events such as completing doctoral programs and finding jobs," says Monnai. "But in Germany, I saw that it was a case of 'people acting once they were prepared,' which means the timing for these events depends on the individual's circumstances. People take their time to think about their future without external timing constraints. This is in total contrast to the situation faced by students in Japan who all try to graduate and get jobs to start on the 1st of April of that fiscal year."

Monnai recalls being impressed by the ability of the German students to clearly explain their intentions in words. "I have heard that in physics exams, students are expected to not only solve equations but also answer questions verbally," explains Monnai. "On TV programs for children, I noticed it was common for ordinary children to explain in their own words not only what they wanted to be in the future, but also why. I felt that this kind of culture was the basis for the 'verbalization of ideas.'"

Focus on terahertz waves and remote heartbeat detection

There are a wide range of applications of electromagnetic waves. For example, microwaves are used for heating meals, infrared rays for monitoring temperature, and X-rays for looking inside matter. However, there is increasing interest in the unexplored terahertz wavelengths. "One of my research themes is focused on terahertz radar with the goal of controlling machines and supporting human cognitive behavior," explains Monnai. "We recently developed a compact, highly penetrating, high-resolution terahertz radar system for application in the fields of mobile/wearable devices and drones. We revealed the power of our technology by demonstrating non-contact and remote detection of human heartbeats where the terahertz radiation penetrated a person's clothes."

Demonstration of non-contact heartbeat detection using a terahertz radar. © Yasuaki Monnai, Keio University

The terahertz frequency band is generally recognized as covering the range from approximately 0.3 THz to around 10 THz, where 'tera' refers to one trillion (1012) cycles per second. This corresponds to the relatively long wavelengths of 1 mm to 0.1 mm when compared to around 500 nm (10-9m) for visible light. Notably, terahertz radiation is noninvasive and not harmful to the human body, thereby offering a wide range of applications ranging from inspecting defects in industrial products to whole body scanners at airports and cancer detection.

Monnai explains that the resolution of terahertz waves is significantly higher than conventional microwaves and millimeter waves, and media are more transparent to terahertz radiation than light enabling better detection. He adds that his group's technology does not require phase shifters, lenses, mechanical scanners, or other such components, thereby enabling a highly compact system without moving parts.

Terahertz waves as data interfaces between the physical world and information technology

It is becoming increasingly clear that the unique properties of terahertz waves have the potential to be extremely useful not only as communications carriers but also as measurement probes.

"Terahertz waves is a next generation technology acting as the interface for incorporating data in the physical world into the cyber world, such as autonomous driving and telepresence," says Monnai. "I believe that we must combine cutting-edge hardware and software for such applications. So currently, I am focusing my research on terahertz systems with smart hardware."

Abstract-Integrated terahertz radar based on leaky-wave coherence tomography

• Hironori Matsumoto, 
• Issei Watanabe, 
• Akifumi Kasamatsum  
• Yasuaki Monnai
• 
  

https://www.nature.com/articles/s41928-019-0357-4

Terahertz wave radar offers a higher resolution and smaller aperture compared with microwave radar. However, despite the emergence of terahertz sources and detectors suitable for radar front ends, the integration of a phased-array radar system remains challenging due to the lack of phase shifters and circulators, the basic components for beam steering and input–output isolation. Here we show that leaky-wave coherence tomography, which can integrate a terahertz radar system using a pair of reverse-connected leaky-wave antennas, can be used to implement beam steering and homodyne detection in one package. Our approach can detect direction and range without using phase shifters, circulators, half-mirrors, lenses or mechanical scanners, providing a compact, penetrating and high-resolution radar system suitable for mobile devices and drones. To illustrate the capabilities of the technique, we use it to create a remote heartbeat detector that can measure the chest displacement of a person through their clothes.

Abstract-Parameter Estimation of the Precessing Targets with a Wideband Terahertz Radar

Qi Yang ; Bin Deng ; Hongqiang Wang ; Yuliang Qin ; Chenggao Luo

https://ieeexplore.ieee.org/document/8510474

In the traditional microwave band, high accuracy parameter estimation is often hard to realize because of the poor resolution. In this paper, a high accuracy parameter estimation method of the precessing targets in the terahertz band was proposed, and an experiment based on a precessing warhead model with a 0.32 THz wideband radar system was carried out. The processing results of the real measured data prove the feasibility and precision of the proposed method, and also show the promising prospects of terahertz radar systems in future military applications.

Abstract-Terahertz radar cross section measurements

Krzysztof Iwaszczuk, Henning Heiselberg, and Peter Uhd Jepsen

Fig. 1 (a) Schematic diagram of the THz RCS setup. (b) 10 cm-long 1:150-scale metal model of aircraft fighter F-16.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-18-25-26399

We perform angle- and frequency-resolved radar cross section (RCS) measurements on objects at terahertz frequencies. Our RCS measurements are performed on a scale model aircraft of size 5-10 cm in polar and azimuthal configurations, and correspond closely to RCS measurements with conventional radar on full-size objects. The measurements are performed in a terahertz time-domain system with freely propagating terahertz pulses generated by tilted pulse front excitation of lithium niobate crystals and measured with sub-picosecond time resolution. The application of a time domain system provides ranging information and also allows for identification of scattering points such as weaponry attached to the aircraft. The shapes of the models and positions of reflecting parts are retrieved by the filtered back projection algorithm.

©2010 Optical Society of America

Radar to spot the bad guys from on high

http://www.china.org.cn/china/2019-02/15/content_74467346.htm

China's space engineers said they can now offer a new method to detect terrorists transporting explosives as well as track moving targets more efficiently than current modalities.

Researchers at the Beijing Institute of Radio Measurement, affiliated with the China Aerospace Science and Industry Corp, said they have developed the country's first terahertz radiation-enabled synthetic-aperture radar and they are working to utilize the technology in public security work.

Li Jun, a senior designer at the institute, explained that a terahertz is a unit of the electromagnetic spectrum between the microwave and the optical wavelengths. Among terahertz radiation's many physical characteristics, it has a special ability to identify proteins, the building blocks of living organisms. It can also detect TNT, one of the most oft used explosive materials, and can therefore be used to detect individuals carrying the material on their persons.

"Currently, it is very difficult for public security authorities to screen people for firearms or explosive devices from long, safe distances. Most methods rely on handheld detectors and visual clues, forcing law-enforcement personnel to check suspected people within a short range or manually and this has proved to be time-consuming and dangerous," Li said.

By comparison, terahertz radiation-enabled radar takes advantage of its high penetration capability, and is able to detect explosives and reveal hidden weapons from afar, which helps to improve safety at public buildings and at large events, as well as the safety of security officers, he said.

In addition to its potential applications in remote detection work, the radar technology also offers better solutions for law enforcement departments' surveillance of criminal suspects or terrorists, Li said.

"Existing optical, infrared or radar systems are subject to a host of external factors such as sunlight, cloud or smog, when they are used to monitor and track people on the move. But terahertz technology is immune to these factors, reducing the risk of losing targets," he said.

The institute is a leading research body in radar and terahertz technology in China and has taken part in the development of many advanced defense technologies. Encouraged by the government's policies to foster transfer of defense technologies to civilian industries, institute designers have been seeking to make use of their expertise to assist other sectors, Li said.

Engineers have built prototypes of terahertz radiation-enabled synthetic-aperture radar and are conducting tests.

"We mounted a prototype on a drone and recently conducted test flights in Shaanxi province," Li said. "A typical application of the radar in the future can be drone-based to help with large-scale detection of explosive-carrying terrorists or the placement of improvised explosive devices. This will be much more efficient and safer than deploying a lot of security personnel to do the same work."

Drones equipped with the radar can also perform uninterrupted surveillance of suspects, he added.

Abstract-Absolute and Precise Terahertz-Wave Radar Based on an Amplitude-Modulated Resonant-Tunneling-Diode Oscillator

Adrian Dobroiu, Ryotaka Wakasugi, Yusuke Shirakawa, Safumi Suzuki,  Masahiro Asada

https://www.mdpi.com/2304-6732/5/4/52

We present the principle of a terahertz-wave radar and its proof-of-concept experimental verification. The radar is based on a 522 GHz resonant-tunneling-diode oscillator, whose terahertz output power can be easily modulated by superimposing the modulation signal on its bias voltage. By using one modulation frequency and measuring the time delay of the returning signal, a relative measurement of the propagation distance is possible; adding a second modulation frequency removes the ambiguity stemming from the periodicity of the modulation sine wave and allows an absolute distance measurement. We verified this measurement method experimentally and obtained a submillimeter precision, as predicted by theory.

Abstract-Translation compensation and micro-Doppler extraction for precession ballistic targets with a wideband terahertz radar

Qi Yang, Bin Deng, Hongqiang Wang,  Ye Zhang, Yuliang Qin,

https://www.spiedigitallibrary.org/journals/Journal-of-Electronic-Imaging/volume-27/issue-1/013009/Translation-compensation-and-micro-Doppler-extraction-for-precession-ballistic-targets/10.1117/1.JEI.27.1.013009.short?SSO=1

Imaging, classification, and recognition techniques of ballistic targets in midcourse have always been the focus of research in the radar field for military applications. However, the high velocity translation of ballistic targets will subject range profile and Doppler to translation, slope, and fold, which are especially severe in the terahertz region. Therefore, a two-step translation compensation method based on envelope alignment is presented. The rough compensation is based on the traditional envelope alignment algorithm in inverse synthetic aperture radar imaging, and the fine compensation is supported by distance fitting. Then, a wideband imaging radar system with a carrier frequency of 0.32 THz is introduced, and an experiment on a precession missile model is carried out. After translation compensation with the method proposed in this paper, the range profile and the micro-Doppler distributions unaffected by translation are obtained, providing an important foundation for the high-resolution imaging and micro-Doppler extraction of the terahertz radar.

© 2018 SPIE and IS&T

Abstract-Three-Dimensional Terahertz Coded-Aperture Imaging Based on Single Input Multiple Output Technology

Shuo Chen, Chenggao Luo,  Bin Deng, Hongqiang Wang, Yongqiang Cheng, Zhaowen Zhuang

http://www.mdpi.com/1424-8220/18/1/303

As a promising radar imaging technique, terahertz coded-aperture imaging (TCAI) can achieve high-resolution, forward-looking, and staring imaging by producing spatiotemporal independent signals with coded apertures. In this paper, we propose a three-dimensional (3D) TCAI architecture based on single input multiple output (SIMO) technology, which can reduce the coding and sampling times sharply. The coded aperture applied in the proposed TCAI architecture loads either purposive or random phase modulation factor. In the transmitting process, the purposive phase modulation factor drives the terahertz beam to scan the divided 3D imaging cells. In the receiving process, the random phase modulation factor is adopted to modulate the terahertz wave to be spatiotemporally independent for high resolution. Considering human-scale targets, images of each 3D imaging cell are reconstructed one by one to decompose the global computational complexity, and then are synthesized together to obtain the complete high-resolution image. As for each imaging cell, the multi-resolution imaging method helps to reduce the computational burden on a large-scale reference-signal matrix. The experimental results demonstrate that the proposed architecture can achieve high-resolution imaging with much less time for 3D targets and has great potential in applications such as security screening, nondestructive detection, medical diagnosis, etc.

Abstract-Dynamic Gesture Recognition with a Terahertz Radar Based on Range Profile Sequences and Doppler Signatures

Zhi Zhou, , Zongjie Cao,    Yiming Pi

http://www.mdpi.com/1424-8220/18/1/10

The frequency of terahertz radar ranges from 0.1 THz to 10 THz, which is higher than that of microwaves. Multi-modal signals, including high-resolution range profile (HRRP) and Doppler signatures, can be acquired by the terahertz radar system. These two kinds of information are commonly used in automatic target recognition; however, dynamic gesture recognition is rarely discussed in the terahertz regime. In this paper, a dynamic gesture recognition system using a terahertz radar is proposed, based on multi-modal signals. The HRRP sequences and Doppler signatures were first achieved from the radar echoes. Considering the electromagnetic scattering characteristics, a feature extraction model is designed using location parameter estimation of scattering centers. Dynamic Time Warping (DTW) extended to multi-modal signals is used to accomplish the classifications. Ten types of gesture signals, collected from a terahertz radar, are applied to validate the analysis and the recognition system. The results of the experiment indicate that the recognition rate reaches more than 91%. This research verifies the potential applications of dynamic gesture recognition using a terahertz radar.

Abstract-Three-Dimensional Imaging of Space Debris with Space-Based Terahertz Radar

 Xu Yang, Yiming Pi,  Tong Liu,   Haijiang Wang

http://ieeexplore.ieee.org/document/8207424/


The increasing natural or man-made space debris could pose a serious threat to orbital space-based systems and their operators. Consequently, their detection, reorganization, and tracking are of considerable significance. However, the traditional solutions, including ground-based radar and optical telescope, can not exactly observe the debris with small diameter. Imaging with space-based terahertz (THz) radar in combination with inverse synthetic aperture radar (ISAR) technique enables us to obtain high-resolution three-dimensional (3-D) image. In this paper, we have developed a high-resolution THz radar that operates at 340 GHz with a bandwidth of 28.8 GHz and the output peak power of 5 mW for proof-of-concept. In addition, using the characteristic that space debris rotates its main axis, we have established a 3-D ISAR imaging geometry as well as its corresponding signal model. Then, a 3-D wavenumber-domain image formation algorithm is presented and has been validated by point target simulation. The experimental results have confirmed that the THz radar can effectively achieve high-resolution 3-D imaging of the spinning space debris.

Abstract-Propagation characteristic of THz wave in camouflage net material

Hailong Dong, Jiachun Wang, Zongsheng Chen,  Zhidan Lin, Dapeng Zhao,  Ruihuang Liu

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10461/104611J/Propagation-characteristic-of-THz-wave-in-camouflage-net-material/10.1117/12.2285538.pdf



Terahertz (THz) radar system, with excellent potentials such as high-resolution and strong penetration capability, is promising in the field of anti-camouflage. Camouflage net is processed by cutting the camouflage net material, which is fabricated on pre-processing substrate by depositing coatings with camouflage abilities in different bands, such as visible, infrared and radar. In this paper, we concentrate on the propagation characteristic of THz wave in camouflage net material. Firstly, function and structure of camouflage net were analyzed. Then the advantage and appliance of terahertz time-domain spectroscopy (THz-TDS) was introduced. And the relevant experiments were conducted by utilizing THz-TDS. The results obtained indicate that THz wave has better penetration capacity in camouflage net material, which demonstrates the feasibility of using THz radar to detect those targets covered with camouflage net.

© (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-A 1.25 THz High Gain Hybrid Circuit with CNT Model Performance Optimization for Radar Sensors Application

Sandeep Kumar, Van-Ha Nguyen, Won-young Jung, Hanjung Song

https://www.springerprofessional.de/en/a-1-25-thz-high-gain-hybrid-circuit-with-cnt-model-performance-o/15125388


This work focuses on a novel approach of hybrid circuit topology with carbon nanotube (CNT) model which provides higher gain at 1.25 THz for radar sensors application. A single walled CNT provides RF circuit model and demonstrates its ability to resonant at terahertz frequencies. The hybrid structure provides a circuit topology which achieves wide impedance bandwidth of 0.33 THz within range of 1.07 to 1.42 THz. A transmission line radiator used as a compensator in order to cancel parasitic capacitance and achieves more than 30 dB forward gain. A minimum noise figure of 0.4 dB is also achieves with tuning effects for inductor of RF circuit model at 1.25 THz. The whole circuit topology is implemented in advanced design system with RF simulator using 45 nm predictive technology model. This fascinating work approach first attempts to make circuit topology at THz for parameters of soil measurement application.

Abstract-Research on imaging of precession targets based on range-instantaneous Doppler in the terahertz band

 Qi Yang,  Bin Deng,  Hongqiang Wang,   Wenxia Ding,   Kang Liu,

http://ieeexplore.ieee.org/document/7968798/

In this paper, a 0.32 THz imaging radar system was built and experiment on a precession warhead model is presented. The imaging algorithm based on range-instantaneous Doppler algorithm is adopted and high resolution ISAR imaging results are obtained. From these imaging results, we can easily recognize structures and even the subtle structures of the precession target, which verify the advantages of terahertz radar in high resolution imaging.

Abstract-Experimental results of concealed object imaging using Terahertz radar

 Yanwen Jiang, Bin Deng, Yuliang Qin, Hongqiang Wang, Ye Zhang,   Xiaoyu Yang

http://ieeexplore.ieee.org/search/searchresult.jsp?newsearch=true&queryText=terahertz

Terahertz imaging has been shown to have the potential to detect objects hidden under common coverings. In this paper, a 360° fast rotating imaging scheme for the detection of concealed objects using terahertz radar is proposed and validated by proof-of-concept experiments. The imaging results of three dangerous objects, i.e. hammer, scissor and metal handgun model, covered with fabric and cardboard are obtained, which demonstrate the effectiveness of the proposed imaging scheme for the concealed object detection with high resolution. The work and results can benefit the development of real-time imaging applications of Terahertz radar.

Abstract-Micro-Doppler Ambiguity Resolution for Wideband Terahertz Radar Using Intra-Pulse Interference

Qi Yang, Yuliang Qin, Bin Deng, Hongqiang Wang, Peng You,

http://www.mdpi.com/1424-8220/17/5/993

Micro-Doppler, induced by micro-motion of targets, is an important characteristic of target recognition once extracted via parameter estimation methods. However, micro-Doppler is usually too significant to result in ambiguity in the terahertz band because of its relatively high carrier frequency. Thus, a micro-Doppler ambiguity resolution method for wideband terahertz radar using intra-pulse interference is proposed in this paper. The micro-Doppler can be reduced several dozen times its true value to avoid ambiguity through intra-pulse interference processing. The effectiveness of this method is proved by experiments based on a 0.22 THz wideband radar system, and its high estimation precision and excellent noise immunity are verified by Monte Carlo simulation.

Abstract-An Effective Nonlinear Phase Compensation Method for FMCW Terahertz Radar

Yanwen Jiang 
Bin Deng ; Hongqiang Wang ; Yuliang Qin ; Kang Liu

http://ieeexplore.ieee.org/xpl/abstractAuthors.jsp?arnumber=7460187&filter%3DAND%28p_IS_Number%3A4581641%29

The nonlinearity of signal usually leads to the range profile blurring and defocusing in the terahertz (THz) radar ranging, which should be compensated to achieve a well-focused range profile. In this paper, an effective nonlinear phase compensation method is proposed to compensate for the signal distortion caused by the radar waveform nonlinearities. It comprises two processing steps, namely, coarse phase compensation and precise phase compensation, which are based on the time-frequency (TF) distribution and the phase gradient autofocus (PGA) algorithm, respectively. The proposed method is a nonparametric method and can eliminate the errors caused by phase discontinuity of the dechirped frequency modulated continuous wave (FMCW) signal. Furthermore, the compensation method can be used in the processing of multi-period real data which are obtained from the FMCW THz radar.

Abstract-Broadband frequency-chirped terahertz-wave signal generation using periodically-poled lithium niobate for frequency-modulated continuous-wave radar application

Junichi Hamazaki, Yoh Ogawa, Norihiko Sekine, Akifumi Kasamatsu, Atsushi Kannno,Naokatsu Yamamoto, Iwao Hosako

National Institute of Information and Communications Technology (Japan)

Proc. SPIE 9747, Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications IX, 97471J (February 25, 2016); doi:10.1117/12.2210936

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2498804

We have proposed a method by using a nonlinear optical technique to generate frequency-modulated (FM) signals in the terahertz (THz) band with much broader bandwidth. Periodically-poled lithium niobates (PPLNs) are excited by ultrashort pulses, and linearly frequency-chirped THz pulses are obtained by changing the periodicity of the PPLN gradually. The bandwidth achieved is approximately 1 THz at a center frequency of 1.5 THz. Using this wave in a FM continuous (CW) radar system is expected to result in a range resolution of ~150 μm. This FM-THz signal generation technique will thus be useful in or future civil safety applications requiring high-resolution ranging or imaging. 
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Terahertz inverse synthetic aperture radar imaging using self-mixing interferometry with a quantum cascade laser

H. S. Lui, T. Taimre, K. Bertling, Y. L. Lim, P. Dean, S. P. Khanna, M. Lachab, A. Valavanis, D. Indjin, E. H. Linfield, A. G. Davies, and A. D. Rakić  »View Author Affiliations
http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-9-2629

We propose a terahertz (THz)-frequency synthetic aperture radar imaging technique based on self-mixing (SM) interferometry, using a quantum cascade laser. A signal processing method is employed which extracts and exploits the radar-related information contained in the SM signals, enabling the creation of THz images with improved spatial resolution. We demonstrate this by imaging a standard resolution test target, achieving resolution beyond the diffraction limit.

© 2014 Optical Society of America

Abstract-HIGH-FREQUENCY METHOD FOR TERAHERTZ RADAR CROSS SECTION OF CONDUCTIVE TARGETS IN FREE SPACE

By H. Hua, Y.-S. Jiang, and Y. He
http://www.jpier.org/PIERB/pier.php?paper=14012702

The high-frequency method for the prediction of the terahertz (THz) radar cross section (RCS) of conductive targets with extremely electrically large size in free space was presented. In order to consider the scattering fields of the perfectly electric conducting (PEC) targets with extremely electrically large size in free space, the Green’s function was introduced into the conventional physical optics (PO) method which was combined with the graphical electromagnetic computing (GRECO) method and improved using the partition display algorithm. The shadow regions were eliminated quickly by displaying lists of OpenGL to rebuild the targets, and the geometry information was attained by reading the color and depth of each pixel. The THz RCS of conductive targets can be exactly calculated in free space. The RCS comparison between the partition display GRECO prediction by the self-written Visual C++ 2010 program and the simulation of FEKO software with the large element PO method proves the validity and accuracy of the proposed method. The results provide an important basis and method for the potential applications of THz radar in many fields such as military, astronomy and remote sensing.

Citation:
H. Hua, Y.-S. Jiang, and Y. He, "High-frequency method for terahertz radar cross section of conductive targets in free space," Progress In Electromagnetics Research B, Vol. 59, 193-204, 2014.
http://www.jpier.org/pierb/pier.php?paper=14012702

Abstract-Terahertz inverse synthetic aperture radar imaging using self-mixing interferometry with a quantum cascade laser

H. S. Lui, T. Taimre, K. Bertling, Y. L. Lim, P. Dean, S. P. Khanna, M. Lachab, A. Valavanis, D. Indjin, E. H. Linfield, A. G. Davies, and A. D. Rakić  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-39-9-2629

Optics Letters, Vol. 39, Issue 9, pp. 2629-2632 (2014)
http://dx.doi.org/10.1364/OL.39.002629

We propose a terahertz (THz)-frequency synthetic aperture radar imaging technique based on self-mixing (SM) interferometry, using a quantum cascade laser. A signal processing method is employed which extracts and exploits the radar-related information contained in the SM signals, enabling the creation of THz images with improved spatial resolution. We demonstrate this by imaging a standard resolution test target, achieving resolution beyond the diffraction limit.

© 2014 Optical Society of America