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-Fabry-Pérot interferometer for sensing polar liquids at terahertz frequencies

David Jahn1, Amin Soltani1, Jan C. Balzer1, Withawat Withayachumnankul2, and Martin Koch

http://aip.scitation.org/doi/abs/10.1063/1.4983780

We propose and validate a sensor for polar liquids that operates in conjunction with terahertz time-domain spectroscopy. The sensor is constructed from an optically thick silicon wafer and a ground plane, separated by a gap into which the liquid is injected. This arrangement represents a Fabry-Pérot interferometer that causes a sharp minimum in the reflection spectrum. Compared to resonance-based sensors, this sensor design can maintain its sharp spectral response when loaded with highly absorbing polar liquids. This overcomes an issue of damped resonance caused by material losses in resonance-based sensors. We report a reflection minimum shift of 8 GHz per percent ethanol in water. The sensor can be readily integrated with a microfluidic channel for real-time fluid monitoring.

Abstract-Periodic sampling errors in terahertz time-domain measurements

Arno Rehn, David Jahn, Jan. C. Balzer, and Martin Koch

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-6-6712

An extensive investigation of the origin and the impact of periodic sampling errors of terahertz time-domain spectroscopy systems is given. We present experimental findings and compare them to a theoretical model which is developed in this work. Special attention is given to the influence on the extraction of the refractive index from measurements. It can be shown that even distortions of the spectrum at frequencies higher than the used bandwidth can have a significant impact on the extracted refractive index.

© 2017 Optical Society of America