Abstract-Broadband antireflection coating for optimized terahertz beam splitters

Weien Lai, Norman Born, Lorenz Maximilian Schneider, Arash Rahimi-Iman, Jan C. Balzer, and Martin Koch
https://www.osapublishing.org/ome/abstract.cfm?uri=ome-5-12-2812

We investigate the potential of anti-ferromagnetic nanofilms as broadband antireflection coatings in the terahertz frequency range. The anti-ferromagnetic layer is modeled by an analytic wave-impedance matching approach. The experimental results of the transmission and reflection measurements demonstrate the effectiveness of our antireflection coatings. Furthermore, we use anti-ferromagnetic nanofilms as antireflection coating for a terahertz beam splitter. Compared with conventional terahertz beam splitters consisting of an uncoated thick silicon wafer, the coated silicon beam splitter has two advantages: elimination of multiple reflections and improvement of the signal-to-noise ratio for terahertz time-domain spectroscopy in reflection geometry.

© 2015 Optical Society of America

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Abstract-Terahertz Metamaterials with Ultrahigh Angular Sensitivity

1. Norman Born^1,*, 
2. Ibraheem Al-Naib²,
3. Christian Jansen¹, 
4. Ranjan Singh³,
5. Jerome V. Moloney⁴, 
6. Maik Scheller⁴and
7. Martin Koch¹

Article first published online: 21 JAN 2015

DOI: 10.1002/adom.201400469

http://onlinelibrary.wiley.com/doi/10.1002/adom.201400469/abstract;jsessionid=20A4686B394E1E6BCBE1CF340A446441.f03t02?deniedAccessCustomisedMessage=&userIsAuthenticated=false

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A novel conceptual design methodology for strongly interacting metamaterials allows an ultrahigh angular sensitivity. Among others, this methodology enables precise sensing of the wave vector or the exclusion of unwanted directional radiation components. By diligently tailoring the dimensions of the primitive unit cell, an orders of magnitude enhanced sensitivity is achieved.

Abstract-Monitoring plant drought stress response using terahertz time-domain spectroscopy

1. Norman Born13 (norman.born@physik.uni-marburg.de), 
2. David Behringer2(david.behringer@biologie.uni-marburg.de), 
3. Sascha Liepelt2(sascha.liepelt@biologie.uni-marburg.de), 
4. Sarah Beyer2 (beyersar@student.hu-berlin.de), 
5. Michael Schwerdtfeger1 (michael.schwerdtfeger@physik.uni-marburg.de), 
6. Birgit Ziegenhagen2 (birgit.ziegenhagen@biologie.uni-marburg.de)and 
7. Martin Koch1 (martin.koch@physik.uni-marburg.de)

http://www.plantphysiol.org/content/early/2014/02/05/pp.113.233601

1. ¹ Faculty of Physics and Material Sciences Center, Philipps-University Marburg;
2. ² Faculty of Biology, Conservation Biology, Philipps-University Marburg

1. ↵* Corresponding author; email: norman.born@physik.uni-marburg.de

1. Published online before print February 2014, doi: http:/​/​dx.​doi.​org/​10.​1104/​pp.​113.​233601Plant Physiology February 2014 pp.113.233601

We present a novel measurement setup for monitoring changes in the leaf water status using non-destructive terahertz time-domain spectroscopy (THz-TDS). Previous studies on a variety of plants showed the principal applicability of THz-TDS. In such setups decreasing leaf water content directly correlates with increasing terahertz transmission. Our new system allows for continuous, non-destructive monitoring of the water status of multiple individual plants each at the same constant leaf position. It overcomes previous drawbacks, which were mainly due to the necessity of relocating the plants. Using needles of silver fir seedlings as test subjects, we show that the transmission varies along the main axis of a single needle due to a variation in thickness. Therefore, a relocation of plants during the measuring period, which was necessary in the previous THz-TDS setups, should be avoided. Furthermore, we show a highly significant correlation between gravimetric water content and respective terahertz transmission. By monitoring the relative change in transmission, we were able to narrow down the permanent wilting point of the seedlings. Thus we established groups of plants with well-defined levels of water stress that could not be detected visually. This opens up the possibility for a broad range of genetic and physiological experiments.