ISBN 9783843925747

978-3-8439-2574-7, Reihe Physik

Jens Neu
Towards Adaptive Metamaterials for the Terahertz Range

237 Seiten, Dissertation Technische Universität Kaiserslautern (2016), Softcover, A5

Zusammenfassung / Abstract

The terahertz range of the electromagnetic spectrum presents many interesting opportunities for both applied and fundamental scientific research. For example, security engineering has recently shown interest in this spectral range, due to the fact that terahertz radiation can penetrate through many polymers, clothing, and paper.

However to implement terahertz scanning systems, advanced optical components including lenses or beam steerer must be investigated. For example, one significant drawback for the terahertz technology is that there are no low-cost, high-efficiency 2D terahertz detectors. Therefore, in order to map a sample, either the sample or the detector/emitter must be raster scanned. In order to accomplish this task, a high-precision, low-maintenance micropositioning system must be integrated into the scanner. In order to replace these mechanical components, the work presented in this thesis implements metamaterial structures to replace static lenses and static beam steerers with adaptive metamaterial counterparts. These metamaterial devices are able to focus the terahertz beam on the sample under investigation, as well as scan the probe beam for mapping applications.

A static metamaterial based beam steerer is presented. The fabricated samples are characterized with spatially resolved terahertz time domain spectroscopy, with a system realized in the presented work. Numerically simulations, as well as experimental investigation, of the sample, demonstrate a steering angle of about 6 degrees.

Six different bandpass- designs are demonstrated in this work, with operating frequencies between 0.4 THz and 2.0 THz. The demonstrated quality factor of the sample reaches values of up to Q = 4. The previously described bandpass filter is then combined with a photo-sensitive silicon layer in order to create an optically-tunable bandpass filter, with a measured modulation depth of 90%.

This work also demonstrates adaptive lenses. The resulting simulation demonstrates a terahertz spot size of 320 µm FWHM. Based on a similar concept an optically-tunable beam steerer is also designed. The tunable beam steerer produces a steering angle of 3.5 degrees, when illuminated with an optical Gaussian beam. Finally, a third adaptive sample, based on electrically-tuning of Schottky contacts is proposed. This sample is designed to produce a steering angle of 7 degrees for narrow band terahertz radiation.