Abstract-The Effect of Humidity and Temperature on Dielectric Fibre–Bound THz Transmission

M. Taherkhani, R. A. Sadeghzadeh, J. Taiber, J. Ornik, M. Koch

https://link.springer.com/article/10.1007%2Fs10762-019-00644-7

We experimentally study the impact of humidity and temperature on the transmission of 120-GHz waves through a solid core fibre of polypropylene without cladding. We find that the transmission is greatly affected by both, an increase in the water vapour density and in the temperature. We attribute this to the growth of a water film around the fibre which attenuates the evanescent field, and to an increasing absorption of the material with increasing temperature.

Abstract-THz Properties of Adhesives

E. Stübling, L. Gomell, S. Sommer, A. Winkel, M. Kahlmeyer, S. Böhm, M. Koch,

https://link.springer.com/article/10.1007/s10762-018-0492-4

We determined the THz properties of 12 different adhesives which are mainly used for industrial purposes. The adhesives applied can be classified according to their chemical structure: epoxy resins, acrylic resins, and polyurethane based materials. This work represents a basis for future studies, which will concentrate on aging effects, including the absorption of water of adhesive joints. Thus, the dielectric properties of the unaged adhesives are investigated and the results of these measurements are described herein.

Abstract-Low-cost 3D printed GRIN lens for terahertz applications

A. I. Hernandez-Serrano, M Weidenbach, S. F. Busch, M. Koch, and E. Castro-Camus
https://www.osapublishing.org/abstract.cfm?uri=Sensors-2016-SeTu3E.4

We used 3D printing as a new technique to make gradient-refractive-index (GRIN) lenses for terahertz applications. This new low-cost lenses are demonstrated to work within the diffraction limit below 800 GHz.

© 2016 OSA

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Abstract-Highly sensitive terahertz dielectric sensor for small-volume liquid samples

A. Soltani1, H. Neshasteh2, A. Mataji-Kojouri2, N. Born1, E. Castro-Camus3,a), M. Shahabadi2 and M. Koch1

a) Author to whom correspondence should be addressed. Electronic mail: enrique@cio.mx

Appl. Phys. Lett. 108, 191105 (2016); http://dx.doi.org/10.1063/1.4949527

http://scitation.aip.org/content/aip/journal/apl/108/19/10.1063/1.4949527?TRACK=RSS

We present a resonator-based sensor for the measurement of the refractive index of dielectric liquidsamples. The proposed sensor operates on the basis of an electromagnetic resonance between a thinmetallic grating and a reflecting ground plane. The fluid whose refractive index is to be measured fills the region between the metallic grating and the ground plane and causes a considerable shift in the resonance frequency (>500 GHz/RIU). The sensor has a relatively simple structure; therefore, it can be manufactured economically on industrial scales.

Abstract-Fabrication of gradient-refractive-index lenses for terahertz applications by three-dimensional printing

A. I. Hernandez-Serrano, M. Weidenbach, S. F. Busch, M. Koch, and E. Castro-Camus
https://www.osapublishing.org/josab/abstract.cfm?uri=josab-33-5-928

In this article we present the design, fabrication, and characterization of gradient-refractive-index lenses for terahertz (THz) applications. The fabrication was performed by three-dimensional printing. These new low-cost lenses were tested using THz time-domain spectroscopy and imaging in order to measure their optical properties. The results show a focusing capacity within the diffraction limit for frequencies below 700 GHz.

© 2016 Optical Society of America

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Abstract-Terahertz meets sculptural and architectural art: Evaluation and conservation of stone objects with T-ray technology

• K. Krügener
• , M. Schwerdtfeger
• , S. F. Busch
• , A. Soltani
• , E. Castro-Camus
• , M. Koch
•  & W. Viöl
• • http://www.nature.com/articles/srep14842

Conservation of cultural heritage is an area where novel scientific techniques are having enormous impact. Given the value and uniqueness of art pieces, non-invasive diagnostic methods are highly appreciated by conservators. Terahertz radiation has shown enormous potential as non-contact probe that can be used for the three-dimensional reconstruction of internal structure of stone-made objects. In this article we report the evaluation of the internal damage state of two art pieces, a medallion from the Castle of Celle and a window sill from the St. Peter of Trier Cathedral. We also used terahertz radiation to follow and assess the restoration process of the window sill. We found that terahertz spectroscopy is an excellent non-destructive evaluation method for stone artwork that shows enormous potential as a tool for conservation.

Abstract-Focus free terahertz reflection imaging and tomography with Bessel beams

S. F. Busch, 

G. E. Town, 

M. Scheller, 

M. Koch

http://link.springer.com/article/10.1007/s10762-014-0129-1


A broadband terahertz (THz) reflection imaging system with high spatial resolution over a large depth of field is reported. A THz axicon lens producing a truncated THz Bessel beam with a linear focus exceeding 120 mm in length, and with the diameter of the central lobe less than 2 mm was used for imaging in a reflection geometry employing a pulsed THz time-domain spectrometer. With numerical post-processing, it was possible to reconstruct the three dimensional shape of the scanned object

Abstract-Disturbing the coherent dynamics of an excitonic polarization with strong terahertz fields

M. J. Drexler, R. Woscholski, S. Lippert, W. Stolz, A. Rahimi-Iman, and M. Koch

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.195304

We present a paper based on combining four-wave mixing and strong fields in the terahertz frequency range to monitor the time evolution of a disturbed excitonic polarization in a multiple quantum well system. Our findings not only confirm a lower field-dependent ionization threshold for higher excitonic states, but furthermore provide experimental evidence for intraexcitonic Rabi flopping in the time domain. These measurements correspond to the picture of a reversible and irreversible transfer as previously predicted by a microscopic theory.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.195304

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• 
• 
• 

Abstract-Disturbing the coherent dynamics of an excitonic polarization with strong terahertz fields

M. J. Drexler, R. Woscholski, S. Lippert, W. Stolz, A. Rahimi-Iman, and M. Koch

https://journals.aps.org/prb/accepted/c907aY1bEf71ff4532829ec048ac14177c73bb7f9

We present a study based on combining Four-Wave-Mixing (FWM) and strong fields in the terahertz frequency range (THz) to monitor the time-evolution of a disturbed excitonic polarisation in a multiple quantum well system. Our findings not only confirm a lower field-dependent ionisation threshold for higher excitonic states but furthermore provide experimental evidence for intra-excitonic Rabi flopping in the time domain. These measurements correspond to the picture of a reversible and irreversible transfer as previously predicted by a microscopic theory.

Abstract-Cost-efficient delay generator for fast terahertz imaging

T. Probst, A. Rehn, S. F. Busch, S. Chatterjee, M. Koch, and M. Scheller  »View Author Affiliations

Optics Letters, Vol. 39, Issue 16, pp. 4863-4866 (2014)
http://dx.doi.org/10.1364/OL.39.004863

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-16-4863

We present a fast and low-cost delay generator for terahertz (THz) waves that transfers a rotational motion of a transparent dielectric cube into an effective THz delay. The device is easily implemented in the THz beam path and allows for coherent sampling over 40 ps with a scan rate of hundreds of hertz. Furthermore, we show that our approach is particularly suitable for fast THz imaging.

© 2014 Optical Society of America

Abstract-Terahertz plastic compound lenses

M. Wichmann, A. S. Mondol, N. Kocic, S. Lippert, T. Probst, M. Schwerdtfeger, S. Schumann, T. Hochrein, P. Heidemeyer, M. Bastian, G. Bastian, and M. Koch  »View Author Affiliations http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-52-18-4186

We present terahertz (THz) lenses made of highly refracting polymeric compounds which provide a better focusing performance and an increased functionality in comparison to conventional THz lenses. Using mixtures consisting of polypropylene (PP) and alumina as well as PP and zinc sulfide allows a significant increase of the refractive index while simultaneously keeping a low extinction and dispersion. With these new material combinations, lenses with an increased focusing capability are realized. This is evaluated by focal plane measurements using a fiber coupled THz time-domain spectrometer.

Abstract-Ultrabroadband terahertz spectroscopy of a liquid crystal

Ultrabroadband terahertz spectroscopy of a liquid crystal

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-20-27-28249
N. Vieweg, B. M. Fischer, M. Reuter, P. Kula, R. Dabrowski, M. A. Celik, G. Frenking, M. Koch, and P. U. Jepsen  »View Author Affiliations

Liquid crystals (LCs) are becoming increasingly important for applications in the terahertz frequency range. A detailed understanding of the spectroscopic parameters of these materials over a broad frequency range is crucial in order to design customized LC mixtures for improved performance. We present the frequency dependent index of refraction and the absorption coefficients of the nematic liquid crystal 5CB over a frequency range from 0.3 THz to 15 THz using a dispersion-free THz time-domain spectrometer system based on two-color plasma generation and air biased coherent detection (ABCD). We show that the spectra are dominated by multiple strong spectral features mainly at frequencies above 4 THz, originating from intramolecular vibrational modes of the weakly LC molecules.

Abstract:Ionization of coherent excitons by strong terahertz fields

B. Ewers, N. S. Köster, R. Woscholski, M. Koch, and S. Chatterjee 
Faculty of Physics and Materials Sciences Center, Philipps-Universität Marburg, Renthof 5, D-35032 Marburg, Germany

G. Khitrova and H. M. Gibbs 
College of Optical Sciences, The University of Arizona, 1630 E. University Boulevard, Tucson, Arizona 85719-0094, USA

A. C. Klettke, M. Kira, and S. W. Koch 
Faculty of Physics and Materials Sciences Center, Philipps-Universität Marburg, Mainzer Gasse 33, D-35032 Marburg, Germany

Received 7 December 2011; revised 16 January 2012; published 6 February 2012

The interaction of coherent excitons with intense, single-cycle terahertz (THz) pulses is investigated. A significant bleaching of the 1s-exciton resonance develops into a splitting of the absorption peak and the emergence of pronounced wings with increasing THz field strength. A quantum-mechanical many-body analysis attributes the experimental observations to a transition from excitonic Rabi flopping to multi-THz-photon ionization and the population of optically dark exciton states with high quantum numbers.

©2012 American Physical Society

URL:

http://link.aps.org/doi/10.1103/PhysRevB.85.075307

DOI:

10.1103/PhysRevB.85.075307

PACS:

78.67.De, 42.65.Re, 78.47.D-