Abstract-Hyperspectral terahertz imaging with electro-optic dual combs and a FET-based detector

Pedro Martín-Mateos, Dovilė Čibiraitė-Lukenskienė, Roberto Barreiro, Cristina de Dios, Alvydas Lisauskas, Viktor Krozer,  Pablo Acedo

https://www.nature.com/articles/s41598-020-71258-6

In this paper, a terahertz hyperspectral imaging architecture based on an electro-optic terahertz dual-comb source is presented and demonstrated. In contrast to single frequency sources, this multi-heterodyne system allows for the characterization of the whole spectral response of the sample in parallel for all the frequency points along the spectral range of the system. This hence provides rapid, highly consistent results and minimizes measurement artifacts. The terahertz illumination signal can be tailored (in spectral coverage and resolution) with high flexibility to meet the requirements of any particular application or experimental scenario while maximizing the signal-to-noise ratio of the measurement. Besides this, the system provides absolute frequency accuracy and a very high coherence that allows for direct signal detection without inter-comb synchronization mechanisms, adaptive acquisition, or post-processing. Using a field-effect transistor-based terahertz resonant 300 GHz detector and the raster-scanning method we demonstrate the two-dimensional hyperspectral imaging of samples of different kinds to illustrate the remarkable capabilities of this innovative architecture. A proof-of-concept demonstration has been performed in which tree leaves and a complex plastic fragment have been analyzed in the 300 GHz range with a frequency resolution of 10 GHz.

Abstract-All‐Dielectric Silicon Metasurface with Strong Subterahertz Toroidal Dipole Resonance

Dimitrios C. Zografopoulos  Antonio Ferraro  José Francisco Algorri  Pedro Martín‐Mateos  Braulio García‐Cámara  Aldo Moreno‐Oyervides  Viktor Krozer  Pablo Acedo  Ricardo Vergaz  José Manuel Sánchez‐Pena  Romeo Beccherelli,

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201900777

A single‐layer, all‐dielectric metasurface exhibiting a strong toroidal resonance in the low‐atmospheric loss radio window of the subterahertz W‐band is theoretically proposed and experimentally demonstrated. The metasurface is fabricated on a high‐resistivity floating‐zone silicon wafer by means of a single‐process, wet anisotropic etching technique. The properties of the toroidal mode of both the constituent dielectric elements and the metasurface are rigorously investigated by means of the multipole decomposition technique and full‐wave simulations. The experimental demonstration of such a compact, all‐silicon metasurface opens new venues of research in the investigation of toroidal modes and the engineering of functional millimeter‐wave components, which can be scaled to terahertz and higher frequencies of the electromagnetic spectrum

Abstract-Imaging and Spectroscopic Sensing with Low-Repetition-Rate Terahertz Pulses and GaN TeraFET Detectors

• Daniel VoßEmail author
• Wissem Zouaghi
• Mehran Jamshidifar
• Sebastian Boppel
• Cormac McDonnell
• James R. P. Bain
• Nils Hempler
• Graeme P. A. Malcolm
• Gareth T. Maker
• Maris Bauer
• Alvydas Lisauskas
• Adam Rämer
• Sergey A. Shevchenko
• Wolfgang Heinrich
• Viktor Krozer
• Hartmut G. Roskos

https://link.springer.com/article/10.1007%2Fs10762-017-0447-1

Aiming for non-destructive testing and security applications, we investigate transmission-mode imaging and spectroscopic sensing using terahertz (THz) pulses from a commercial optical parametric oscillator (OPO) in combination with THz detectors based on antenna-coupled field-effect transistors (TeraFETs). The Q-switched OPO generates quasi-continuous-wave THz pulses with a peak power of up to 1 W at a repetition rate between 12 and 90 Hz. The pulses are frequency-tunable between 0.7 and 2.6 THz with a typical linewidth of 50 GHz. We explore detection with fast GaN/AlGaN TeraFETs which hold the potential for multi-pixel and homodyne detection.

Abstract-Exploration of Terahertz Imaging with Silicon MOSFETs

• Alvydas Lisauskas, 
• Maris Bauer, 
• Sebastian Boppel, 
• Martin Mundt, 
• Bassam Khamaisi, 
• Eran Socher,
• Rimvydas Venckevičius, 
• Linas Minkevičius, 
• Irmantas Kašalynas, 
• Dalius Seliuta, 
• Gintaras Valušis, 
• Viktor Krozer, 
• Hartmut G. Roskos, 

• http://link.springer.com/article/10.1007%2Fs10762-013-0047-7

We summarize three lines of development and investigation of foundry-processed patch-antenna-coupled Si MOSFETs as detectors of THz radiation: (i) Exploiting the pinciple of plasma-waved-based mixing in the two-dimensional electron gas of the transistors’ channels, we demonstrate efficient detection at frequencies as high as 9 THz, much above the transit-time-limited cut-off frequencies of the devices (tens of GHz). Real-time imaging at 600 GHz with a 12 × 12 detector array is explored. (ii) Given the limited THz power usually available for applications, we explore imaging with enhanced sensitivity in heterodyne mode. We show that real-time operation of a 100 × 100-pixel heterodyne camera should be possible at 600 GHz with a better dynamic range (30 dB) than for direct power detection (20 dB), even if only a quarter-milliwatt of local-oscillator power, distributed radiatively over all detector pixels, is available. (iii) Finally, we present an all-electronic raster-scan imaging system for 220 GHz entirely based on CMOS devices, combining the CMOS detectors with an emitter circuit implemented in a 90-nm CMOS process and delivering radiation with a power on the 100- μW scale. Considering progress in the field, we anticipate that the emitter concept of oscillator-based power generation with on-chip frequency multiplication will carry well into the sub-millimeter-wave regime.

Terahertz in Germany-A gentle look through

02 Oct 2013

Source: Berlin Adlershof

http://www.research-in-germany.de/dachportal/en/Infoservice/News/2013/10/2013-09-30-terahertz-rays-are-good-for-more-than-just-body-scans-at-airports.-fbh-is-one-of-the-world-leading-institutes.html

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Terahertz rays are good for more than just body scans at airports. FBH is one of the world leading institutes

The terahertz technology will soon be arousing interest for many applications in medicine, radar, communications, security, nondestructive materials testing, and quality assurance. The path that must be taken is being paved e.g. by researchers and their integrated componentry at the Ferdinand-Braun-Institut.
Whenever terahertz technology is mentioned, people think of the notorious “strip scanners” that can see through the clothing of air passengers. But this is a hasty reaction. Viktor Krozer, who holds an enclosed professorship of Terahertz Electronics at the Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik (FBH), puts it clearly: “That equipment has little to do with THz technology because it works with essentially lower frequencies.”
Many applications
A terahertz (THz) describes a frequency of one trillion vibrations a second. This can dramatically increase the resolution of conventional imaging systems. Yet this radiation can do more than penetrate packaging and clothes. “Imaging systems of this kind can also be used in industrial quality assurance, medical engineering, and broadband wireless communications,” explained Kozer. He continued that as early as the pilot applications THz was being used for nondestructive materials testing, e.g. for detecting fine hairline cracks in pipeline jackets – or damage in the connecting structures of wind turbine and aircraft rotor blades. “These applications are being pushed forward on a massive scale,” explained Krozer.
Pharmaceuticals companies are hoping that high frequency radiation can better control, for instance, the quality of capsule coatings. The food industry can analyse the quality of fresh goods like fish or meat by directing noncontracting THz technology through the walls of packaging.
Think the previously unthinkable
The crucial advantage of terahertz technology: it can penetrate many materials, but the low energy of its photons does not induce ionisation, making it suitable for many applications. Krozer expects initial marketable applications in three to five years. Until then, he and his team will be paving the way and meanwhile are regarded as one of the world leading institutes in this field. Here, they research and develop new integrated terahertz sources and detectors based on semiconductors. Among their achievements, the scientists have developed a unique semiconductor process that can realise complete system components with integrated circuitry. A complex field for absolute specialists with the courage to think the previously unthinkable. “We’re operating at the limits of the feasible,” commented Krozer casually.
By Chris Löwer for Adlershof Special
www.fbh-berlin.de