Abstract-Terahertz thickness determination with interferometric vibration correction for industrial applications

Tobias Pfeiffer, Stefan Weber, Jens Klier, Sebastian Bachtler, Daniel Molter, Joachim Jonuscheit, and Georg Von Freymann

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-10-12558

In many industrial fields, like automotive and painting industry, the thickness of thin layers is a crucial parameter for quality control. Hence, the demand for thickness measurement techniques continuously grows. In particular, non-destructive and contact-free terahertz techniques access a wide range of thickness determination applications. However, terahertz time-domain spectroscopy based systems perform the measurement in a sampling manner, requiring fixed distances between measurement head and sample. In harsh industrial environments vibrations of sample and measurement head distort the time-base and decrease measurement accuracy. We present an interferometer-based vibration correction for terahertz time-domain measurements, able to reduce thickness distortion by one order of magnitude for vibrations with frequencies up to 100 Hz and amplitudes up to 100 µm. We further verify the experimental results by numerical calculations and find very good agreement.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz Radome Inspection

Fabian Friederich, Karl Henrik May, Bessem Baccouche, Carsten Matheis, Maris Bauer, Joachim Jonuscheit, Michael Moor, David Denman, Jamie Bramble, Nick Savage,

http://www.mdpi.com/2304-6732/5/1/1

Radomes protecting sensitive radar, navigational, and communications equipment of, e.g., aircraft, are strongly exposed to the environment and have to withstand harsh weather conditions and potential impacts. Besides their significance to the structural integrity of the radomes, it is often crucial to optimize the composite structures for best possible radio performance. Hence, there exists a significant interest in non-destructive testing techniques, which can be used for defect inspection of radomes in field use as well as for quality inspection during the manufacturing process. Contactless millimeter-wave and terahertz imaging techniques provide millimeter resolution and have the potential to address both application scenarios. We report on our development of a three-dimensional (3D) terahertz imaging system for radome inspection during industrial manufacturing processes. The system was designed for operation within a machining center for radome manufacturing. It simultaneously gathers terahertz depth information in adjacent frequency ranges, from 70 to 110 GHz and from 110 to 170 GHz by combining two frequency modulated continuous-wave terahertz sensing units into a single measurement device. Results from spiraliform image acquisition of a radome test sample demonstrate the successful integration of the measurement system.

Abstract-Interferometry-aided terahertz time-domain spectroscopy

Daniel Molter, Manuel Trierweiler, Frank Ellrich, Joachim Jonuscheit, and Georg Von Freymann

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-7-7547

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.

© 2017 Optical Society of America