Abstract-Quantitative Assessment of Rock-Coal Powder Mixtures by Terahertz Time Domain Spectroscopy

 Jingjing Deng, Fatima Taleb, Jan Ornik, Enjie Ding, Martin Koch,  Enrique Castro-Camus 

https://link.springer.com/article/10.1007/s10762-021-00803-9

The enormous risk that mine environments impose to the staff directly involved in the mineral extraction process makes the use of automated technologies extremely relevant, in order to minimize the risk of operators . Coal still represents a significant proportion of the fuel supply in several countries such as China, and mining it is an activity of tremendous economic importance . In this letter, we present terahertz (THz) spectroscopy as a potential tool for the quantitative recognition of rock-coal mixtures in powder form. This could lead to the implementation of appropriate sensors for in-line feedback to mining equipment in order to avoid or, at least, minimize the extraction of unwanted surrounding rock without the direct presence of human operators.

Abstract-Recognition of coal from other minerals in powder form using terahertz spectroscopy

 

Jingjing Deng, Jan Ornik, Kai Zhao, Enjie Ding, Martin Koch, and Enrique Castro-Camus

 We show micrographs of the powders produced, the bottom of each image shows a ruler with a spacing of 1mm between marks. The samples shown are Siltstone (a) sieve 1 (691 𝜇$\mu$m-1204 𝜇$\mu$m) and (b) sieve 5 (222 𝜇$\mu$m-512 𝜇$\mu$m), as well as Fat coal (c) sieve 1 (691 𝜇$\mu$m-1204 𝜇$\mu$m) and (d) sieve 5 (222 𝜇$\mu$m-512 𝜇$\mu$m

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-21-30943

Currently a significant fraction of the world energy is still produced from the combustion of mineral coal. The extraction of coal from mines is a relatively complex and dangerous activity that still requires the intervention of human miners, and therefore in order to minimize risks, automation of the coal mining process is desirable. An aspect that is still under investigation is potential techniques that can recognize on-line if the mineral being extracted from the mine is coal or if it is the surrounding rock. In this contribution we present the proof of concept of a method that has potential for recognition of the extraction debris from mining based on their terahertz transmission.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Repeatability of material parameter extraction of liquids from transmission terahertz time-domain measurements

Jan Ornik, Jannik Lehr, Marco Reuter, David Jahn, Felipe Beltran-Mejia, Jan C. Balzer, Thomas Kleine-Ostmann, and Martin Koch

 Experimental setup composed of a pair of photoconductive antennas, a delay line and a femtosecond fiber laser emitting at 780 nm. The laser beam forms the optical path as depicted by the red lines. The blue region represents the THz radiation that impinges one of the five cuvettes.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-19-28178

Recently, many research groups worldwide have reported on the THz properties of liquids. Often these parameters, i.e., refractive index and absorption coefficient, are determined using liquids in cuvettes and terahertz time-domain spectroscopy. Here, we discuss the measurement process and determine how repeatable such measurements and the data extraction are using rapeseed oil as a sample. We address system stability, cuvette positioning, cuvette cleaning and cuvette assembly as sources affecting the repeatability. The results show that system stability and cuvette assembly are the most prominent factors limiting the repeatability of the THz measurements. These findings suggest that a single cuvette with precise positioning and thorough cleaning of the cuvette delivers the best discrimination among different liquid samples. Furthermore, when using a single cuvette and measurement systems of similar stability, the repeatability calculated based on several consecutive measurements is a good estimate to tell whether samples can be discriminated.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz Inspection of Buildings and Architectural Art

Kirsti Krügener,  Jan Ornik,  Lorentz M. Schneider, Alexander Jäckel, Corinna L. Koch-Dandolo,  Enrique Castro-Camus, Nicole Riedl-Siedow, Martin Koch, Wolfgang Viöl

https://www.mdpi.com/2076-3417/10/15/5166

We present a broad literature review on the uses of terahertz radiation for the inspection architectural art, as well as building structures. As an example of the uses of terahertz in this field, we also include original results on a non-destructive assessment of a conservation intervention on murals of the Konstantinbasilika in Trier, Germany while using terahertz time-of-flight spectroscopy.

Abstract-High quality terahertz glass wave plates

Jan Ornik, Leonie Gomell, Stefan F. Busch, Martin Hermans, Martin Koch

Fig. 1 a) Photo of wave plate 1 with an edge of a Euro coin for size comparison. b) Microscope image of the same wave plate. Bright and black stripes correspond to glass bars and air grooves, respectively. They are all of equal thickness, i.e. thickness of the wave plate. Note the difference in the width between glass bars and air grooves.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-25-32631

In this paper we present four λ/2-wave plates made out of fused silica glass for operation in the terahertz frequency range. The design of the wave plates is based on form birefringence. They were fabricated by selective laser-induced etching resulting in a series of glass bars separated by air grooves. Wave plates operating at single, two and several frequencies were designed, fabricated and characterized.

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