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Papers by Joachim Jonuscheit

2023 20th European Radar Conference (EuRAD)

We report on the realization of a 3D terahertz imaging system for industrial radome inspection. T... more We report on the realization of a 3D terahertz imaging system for industrial radome inspection. The system has been designed to be operated within a machining center for radome manufacturing. In order to provide the required flexibility in respect to image resolution and penetration depth, we developed a system, which combines two frequency-modulated continuous-wave terahertz sensing units, operating in adjacent frequency ranges, from 70 to 110 GHz and from 110 to 170 GHz, respectively. The collinear arrangement of the measurement paths does not only allow to simultaneously gather terahertz images in two different frequency ranges, but also to perform data fusion for additional images with increased depth resolution.

Terahertz measurement techniques reveal a high potential for non-destructive and contactless thic... more Terahertz measurement techniques reveal a high potential for non-destructive and contactless thickness determination of thin-coated plastics, ceramics, paper and tablets as well as painted car bodies. While for these applications the thickness is measured at the end of the complete coating process, we here investigate the suitability of this technique in order to determinate the thickness immediately after application of the wet paint. With a self-calibration algorithm, we are able to determine not only the thickness but also the refractive index and extinction coefficient of the coating in wet state simultaneously.

Optics Express, Mar 23, 2017

Terahertz time-domain spectroscopy as well as all optical pump-probe techniques with ultrashort p... more Terahertz time-domain spectroscopy as well as all optical pump-probe techniques with ultrashort pulses relies on the exact knowledge of an optical delay between related laser pulses. Classical realizations of the measurement principle vary the optical path length for one of the pulses by mechanical translation of optical components. Most commonly, only an indirect measurement of the translation is carried out, which introduces inaccuracies due to imprecise mechanics or harsh environment. We present a comprehensive study on the effect of delay inaccuracies on the quality of terahertz spectra acquired with time-domain spectroscopy systems and present an interferometric technique to directly acquire the optical delay simultaneously to the terahertz measurement data. This measurement principle enables high-precision terahertz spectroscopy even in harsh environment with non-systematic disruptions.

We present an online layer-thickness measurement system capable of assessing multiple sub-wavelen... more We present an online layer-thickness measurement system capable of assessing multiple sub-wavelength layers at a data rate of 1.6 kHz. Combining an ultrafast terahertz time-domain spectroscopy engine based on electronically controlled optical sampling (ECOPS) with a highly efficient CPU-based evaluation algorithm, an industry-ready measurement system is realized. To evaluate the performance, we quantify the thickness of multilayer paint samples on aluminum substrates.

Conference on Lasers and Electro-Optics, Jun 21, 2015

We demonstrate THz near-field imaging and spectroscopy at length scales as small as ca. 25 nm bas... more We demonstrate THz near-field imaging and spectroscopy at length scales as small as ca. 25 nm based on integration of a standard THz-TDS system into a commercial scattering-type Scanning Near-field Optical Microscopy (s-SNOM) system.

Journal of Raman Spectroscopy, 2000

ABSTRACT The Q-branches of the ν1 fundamental bands of 14NH3 and 15NH3 were recorded by continuou... more ABSTRACT The Q-branches of the ν1 fundamental bands of 14NH3 and 15NH3 were recorded by continuous-wave coherent anti-Stokes Raman spectroscopy (CARS) at different pressures. Examples of the spectra at pressures from 1.4 to 5.0 kPa and the assignment of the observed lines are presented. For 14NH3 new experimental values for the Raman wavenumbers of K = 0 transitions were determined and for 15NH3 experimental wavenumbers of 71 IR and 56 Raman transitions are listed. Copyright © 2000 John Wiley & Sons, Ltd.

Journal of Raman Spectroscopy, Aug 1, 1995

... CCC 0377-0486/95/0S0699-07 0 1995 by John Wiley & Sons, Ltd. ... 11 4,454 (1 985). 6.... more ... CCC 0377-0486/95/0S0699-07 0 1995 by John Wiley & Sons, Ltd. ... 11 4,454 (1 985). 6. H. Frunder, R. Angstl, D. Illig, HW Schrotter, L. Lechuga-Fossat, JM Flaud, C. Camy-Peyret and WF Murphy, Can. ... 7. S. Zeindl, K. Sailer, F. Bauer, HW Schrotter and A. Ruoff, J. Mol. Sfruct. ...

Imaging systems operating in the sub-terahertz frequency range have proven to be highly attractiv... more Imaging systems operating in the sub-terahertz frequency range have proven to be highly attractive devices for non-destructive testing applications. Especially frequency modulated system concepts have shown a great potential for volume inspection in industrial process and quality control, but often lack fast image acquisition times. We report on the development of a line array system for fast sub-terahertz imaging applications. The realized system employs a sparse array consisting of 12 emitters and 12 heterodyne receivers and operates in the W frequency band between 75 GHz and 110 GHz. The applied stepped-frequency continuous-wave radar concept provides 35 GHz modulation bandwidth for fast volume inspections of large test objects in combination with a band-conveyor.

We present a pulsed THz Imaging System with a line focus intended to speed up measurements. A bal... more We present a pulsed THz Imaging System with a line focus intended to speed up measurements. A balanced 1-D detection scheme working with two industrial line-scan cameras is used. The instrument is implemented without the need for an amplified laser system, increasing the industrial applicability. The instrumental characteristics are determined.

2022 47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), Aug 28, 2022

We present robust terahertz emitter and detector modules, based on LTG-GaAs photoconductive anten... more We present robust terahertz emitter and detector modules, based on LTG-GaAs photoconductive antennas with nonlinear second-harmonic generation for the use in 1550 nm terahertz time-domain spectroscopy systems. With two different dipole antenna-structures with 20 µm and 60 µm dipole length, the spectral performance of pitch-catch transceivers is adjustable. We achieve peak dynamic ranges of up to 87.7 dB and bandwidths of more than 5.5 THz for 5 minutes integration time.

Springer eBooks, 1996

The investigation and analysis of rotation-vibrational bands through high resolution infrared and... more The investigation and analysis of rotation-vibrational bands through high resolution infrared and Raman spectroscopy is an important source of information on the structure of polyatomic molecules. By cw-CARS (coherent anti-Stokes Raman scattering) an instrumental spectral resolution of less than 30 MHz can be routinely achieved. It is limited by the convoluted linewidths of the lasers used for excitation, namely a fixed frequency laser and a tunable dye laser. The CARS signal is generated when the frequency difference of the two lasers coincides with a Raman active rovibrational transition in the molecule.

We report on the development of a stepped frequency continuous wave THz imaging system for proces... more We report on the development of a stepped frequency continuous wave THz imaging system for process control in industrial environments. The system is based on a sparse line array consisting of 12 emitters and 12 heterodyne receivers operating in a frequency range between 75 GHz and 110 GHz. The applied multiple-input and multiple-output technique allows the reconstruction of THz images with 144 virtual pixels per line, while a band-conveyer below the line array provides the required feed motion of the sample for 3-D data acquisition.

Ultra wide-band frequency-modulated continuous-wave imaging systems operating in the lower terahe... more Ultra wide-band frequency-modulated continuous-wave imaging systems operating in the lower terahertz regime have proven to be highly desirable for non-destructive testing applications. However, either quasi-optical configurations or the characteristics of typically used antennas as well as temperature-dependent nonlinear frequency sweeps restrict the achievable spatial resolution and reliability of these systems. In this contribution we report on the implementation of a dielectric rectangular rod antenna and a software-assisted feedback control loop to overcome these limitations.

2016 41st International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz), 2016

Terahertz imaging solutions for industrial non-destructive testing applications receive an increa... more Terahertz imaging solutions for industrial non-destructive testing applications receive an increasing attention. Besides the need for real-time acquisition and image processing, 3D feature localization and large field of views of several tenths to a few meters are in the focus of interest. For this purposes sparse line arrays of transmitters (Tx) and receivers (Rx) offer an optimal approach to reduce costs, hardware complexity and potentially the required measurement time of the system, while providing a comparable imaging quality to full array based approaches. But in the presence of dominant specular reflections, sparse arrays can lead to an inhomogeneous illumination which impairs images and hampers their correct interpretation. We propose an experimentally verified method to simulative asses the design of sparse line arrays, taking in consideration the scattering characteristics of the object under test.

Handbook of Advanced Non-Destructive Evaluation, 2020