Abstract-Qualitative and quantitative analysis of terahertz gas-phase spectroscopy using independent component analysis

Zhijie Li, Nick Rothbart, Xiaojiao Deng, Hua Geng, Xiaoping Zheng, Philipp Neumaier, Heinz-Wilhelm Hübers, 



https://www.sciencedirect.com/science/article/abs/pii/S0169743920300307

This study aims at the qualitative and quantitative analysis of the absorption spectra of gas mixtures measured around 245 GHz. Gas-phase spectra of several volatile organic compounds were measured at different pressures. Based on these spectral data, the independent component analysis (ICA) was applied to recover the components’ spectra and predict their relative concentrations. It is demonstrated that the ICA method is a promising tool to decompose the mixture spectra contributing to high-accuracy qualitative and quantitative analysis of terahertz gas-phase spectroscopy.

Abstract-Analysis of Human Breath by Millimeter-Wave/Terahertz Spectroscopy

Nick Rothbart,  Olaf Holz, Rembert Koczulla, Klaus Schmalz,  Heinz-Wilhelm Hübers

https://www.mdpi.com/1424-8220/19/12/2719/pdf

Breath gas analysis is a promising tool for medical research and diagnosis. A particularly powerful technological approach is millimeter-wave/terahertz (mmW/THz) spectroscopy, because it is a very sensitive and highly selective technique. In addition, it offers the potential for compact and affordable sensing systems for wide use. In this work, we demonstrate the capability of a mmW/THz spectrometer for breath analysis. Samples from three volunteers and a sample from ambient air were analyzed with respect to 31 different molecular species. High-resolution absorption spectra were measured by scanning two absorption lines from each species. Out of the 31, a total of 21 species were detected. The results demonstrate the potential of mmW/THz spectroscopy for breath analysis.

Abstract-Mask Responses for Single-Pixel Terahertz Imaging

Sven Augustin, Sven Frohmann, Peter Jung, Heinz-Wilhelm Hübers

https://www.nature.com/articles/s41598-018-23313-6

Terahertz (THz) radiation meaning electromagnetic radiation in the range from 0.1 (3) to 10 (30) has the unique advantage of easily penetrating many obstructions while being non-hazardous to organic tissue since it is non-ionizing. A shortcoming of this domain is the limited availability of high-sensitivity detector arrays respective THz cameras with >1k pixels. To overcome the imaging limitations of the THz domain, compressive imaging in combination with an optically controllable THz spatial light modulator is a promising approach especially when used in a single-pixel imaging modality. The imaging fidelity, performance and speed of this approach depend crucially on the imaging patterns also called masks and their properties used in the imaging process. Therefore, in this paper, it is investigated how the image quality after reconstruction is specifically influenced by the different mask types and their properties in a compressive imaging modality. The evaluation uses an liquid-crystal display based projector as spatial light modulator to derive specific guidelines for the use of binary and true greyscale masks in THz single-pixel imaging setups respective THz single-pixel cameras when used in far-field applications e.g. stand-off security imaging.

Abstract-First Terahertz-range Experiments on Pump – Probe Setup at Novosibirsk free Electron Laser

Yulia Yu.Choporova, Vasily V.Gerasimov, Boris A.Knyazev, Sergey M.Sergeev, Oleg A.Shevchenko, Roman Kh.Zhukavin, Nikolay V.Abrosimov, Konstantin A.Kovalevsky, Vladimir K.Ovchar, Heinz-Wilhelm Hübers, Gennady N.Kulipanov, Valery N.Shastin, Harald Schneider, Nikolay A.Vinokurov

https://www.sciencedirect.com/science/article/pii/S1875389216303224

A single-color pump-probe system has been commissioned at the Novosibirsk free electron laser. The laser emits a tunable monochromatic terahertz radiation. To prove the proper system operation, we investigated the time-resolved absorption of a sample of n-type germanium doped with antimony, which was previously investigated at the FELBE facility, in the temperature range from 5 to 40 K. The measured relaxation time amounted to about 1.7 ns, which agreed with the results obtained at the FELBE. The results of pump-probe measurements of non-equilibrium dynamics of hot electrons in the germanium crystal at cryogenic temperatures are presented for wavelengths of 105, 141 and 150 μm.

Abstract- Gas Spectroscopy System for Breath Analysis at mm-wave/THz Using SiGe BiCMOS Circuits

 Klaus Schmalz,   Nick Rothbart ,  Philipp F.-X. Neumaier,  Johannes Borngräber,   Heinz-Wilhelm Hübers,  Dietmar Kissinger

http://ieeexplore.ieee.org/document/7836317/

The unique fingerprint spectra of volatile organic compounds for breath analysis and toxic industrial chemicals make an mm-wave (mmW)/THz gas sensor very specific and sensitive. This paper reviews and updates results of our recent work on sensor systems for gas spectroscopy based on integrated transmitter (TX) and receiver (RX), which are developed and fabricated in IHP's 0.13 μm SiGe BiCMOS technology. In this paper, we present an mmW/THz spectroscopic system including a folded gas absorption cell of 1.9 m length between the TX and RX modules. We discuss the results and specifications of our sensor system based on integrated TX and RX. We demonstrate TXs and RXs with integrated antennas for spectroscopy at 238-252 GHz and 494-500 GHz using integer-N phase-locked loops (PLLs). We present a compact system by using fractional-N PLLs allowing frequency ramps for the TX and RX, and for TX with superimposed frequency shift keying or reference frequency modulation. In another configuration, the voltage controlled oscillators of the TX and RX local oscillator are tuned directly without PLLs by applying external voltages. Further developments of our system are aimed at realizing an even wider frequency span by switching between frequency bands, and to use a more compact gas absorption cell.

Abstract-High-spectral-resolution terahertz imaging with a quantum-cascade laser

Till Hagelschuer, Nick Rothbart, Heiko Richter, Martin Wienold, Lutz Schrottke, Holger T. Grahn, and Heinz-Wilhelm Hübers

https://www.osapublishing.org/oe/abstract.cfm?URI=oe-24-13-13839

We report on a high-spectral-resolution terahertz imaging system operating with a multi-mode quantum-cascade laser (QCL), a fast scanning mirror, and a sensitive Ge:Ga detector. By tuning the frequency of the QCL, several spectra can be recorded in 1.5 s during the scan through a gas cell filled with methanol (CH3OH). These experiments yield information about the local absorption and the linewidth. Measurements with a faster frame rate of up to 3 Hz allow for the dynamic observation of CH3OH gas leaking from a terahertz-transparent tube into the evacuated cell. In addition to the relative absorption, the local pressure is mapped by exploiting the effect of pressure broadening.

© 2016 Optical Society of America

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Abstract-Granular Structure Determined by Terahertz Scattering

Philip Born, Nick Rothbart, Matthias Sperl, Heinz-Wilhelm Hübers
 (Submitted on 23 Dec 2013)
http://arxiv-web3.library.cornell.edu/abs/1312.6519

 Light-scattering in the terahertz region is demonstrated for granular matter. A quantum-cascade laser is used in a benchtop setup to determine the angle-dependent scattering of spherical grains as well as coffee powder and sugar grains. For the interpretation of the form factors for the scattering from single particles one has to go beyond the usual Rayleigh-Gans-Debye theory and apply calculations within Mie theory. In addition to single scattering also collective correlations can be identified and extracted as a static structure factor.

The terahertz Universe as depicted in new textbook

Terahertz Techniques, a textbook that deals with all aspects of terahertz technology, is now available. Heinz-Wilhelm Hübers is head of the Department of Experimental Planetary Physics at the German Aerospace Center (DLR) Institute of Planetary Research and a professor at the Technische Universität Berlin. Together with Erik Bründermann from the Ruhr University Bochum and Maurice Fitzgerald Kimmitt from the University of Essex, he is one of the three authors of the book published by Springer Verlag. The textbook is a coherent and didactically clearly structured text that communicates the basics as well as providing a comprehensive overview of the current state of scientific knowledge for students and researchers who wish to enter this interesting and rapidly developing field of research.

Formation and evolution of stars

Research into the terahertz range of the electromagnetic spectrum and the development of innovative technologies for its exploitation have progressed at great speed in the last 15 years. The authors of Terahertz Techniques have made crucial contributions in this respect; Kimmitt played a key role in the development of the first terahertz laser in the world. "Although a lot has happened in the field of terahertz research in the last few years, there has never been a textbook that comprehensively covers this highly topical research field," Professor Hübers comments. "The use of terahertz technologies is of particular interest to astronomy and planetary research, as observations in this range of the spectrum can contribute significantly to our understanding of the origin and development of stars, planets and smaller celestial bodies, such as comets or asteroids," Hübers continues. "It is, however, only one part of terahertz research," he added. "Other research fields are spectroscopy and imaging, for example in security applications, quality assurance and industrial process control. There are also potential new areas of application in chemistry, biology and medicine."

A comprehensive book

In almost 400 pages and an introductory chapter on the history of this research field, the Terahertz Techniquestextbook offers detailed information about its basics, the materials, radiation sources, detectors as well as spectroscopy and imaging in the terahertz range. The connection with current research is established by references to more detailed relevant articles. The clear structure guides the reader through the various aspects of terahertz technology. Numerous vivid graphics and pictures supplement the content. An index makes it quick and easy to look up a topic, and the comprehensive bibliography with more than 700 references allows for deeper study. This makes the book suitable both as a general introduction to the subject for students, and as an indispensable reference work for anyone working or intending to work in this exciting research field.