Abstract-2D tomographic terahertz imaging using a single pixel detector

Till Mohr, Andreas Herdt, and Wolfgang Elsässer

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-3-3353

A 2D tomographic terahertz imaging set-up using a single pixel imaging approach is realized, where a liquid helium cooled bolometer is utilized as a bucket detector and a mercury-arc lamp serves as a broadband terahertz source. The different patterns of the terahertz radiation, which are necessary for the single pixel imaging approach, are realized by spatially addressed photodoping of a high resistivity float zone silicon window, employing a near-infrared laser diode, which is spatially modulated by a digital micromirror device. The two investigated sample objects have cylindrical and cuboid shapes and consist of polypropylene. Both sample shapes cause strong influences of refraction, reflection and diffraction, which distort the measured projections and thus have to be considered in the tomographic reconstruction. In order to consider these effects, a model is developed which combines refraction and diffraction effects by a hybrid approach using ray tracing and scalar diffraction theory yielding finally projections of the sample objects. These simulated projections are compared to the measured projections and show a good agreement between the experimental results and the developed model. In accordance with this result, an optimization problem is formulated, which offers an approach for tomographic reconstruction using the developed model.

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

Abstract-Two novel experimental schemes for terahertz tomography

Till Mohr,  Wolfgang Elsäßer,

http://ieeexplore.ieee.org/document/8024769/

In this contribution, we present two novel and compact terahertz tomography spectroscopy concepts. First, we exploit continuous-wave (CW) terahertz radiation generation and phase-sensitive detection in the same single photoconductive antenna (PCA), a homodyne self-mixing detection approach and apply it within a 2D terahertz tomography imaging application where we reconstruct the two-dimensional image of a hollow-core Teflon cylinder filled with α-lactose as a proof-of-concept demonstration. Second, we realize a single-pixel tomography scheme where 2D tomographic spatial information is achieved by spatially-resolved photodoping of a high-resistivity silicon wafer plate giving rise to fast transverse single-pixel information (via a digital micro mirror device (DMD)) with the subsequent rotation of the object for tomography. Both concepts offer a significantly reduced complexity and consequently lower cost of the terahertz spectroscopy set-up and their THz performance will be discussed and compared.

Abstract-Two-dimensional tomographic terahertz imaging by homodyne self-mixing

Till Mohr, Stefan Breuer, G. Giuliani, and Wolfgang Elsäßer
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-21-27221

We realize a compact two-dimensional tomographic terahertz imaging experiment involving only one photoconductive antenna (PCA) simultaneously serving as a transmitter and receiver of the terahertz radiation. A hollow-core Teflon cylinder filled with α-Lactose monohydrate powder is studied at two terahertz frequencies, far away and at a specific absorption line of the powder. This sample is placed between the antenna and a chopper wheel, which serves as back reflector of the terahertz radiation into the PCA. Amplitude and phase information of the continuous-wave (CW) terahertz radiation are extracted from the measured homodyne self-mixing (HSM) signal after interaction with the cylinder. The influence of refraction is studied by modeling the set-up utilizing ZEMAX and is discussed by means of the measured 1D projections. The tomographic reconstruction by using the Simultaneous Algebraic Reconstruction Technique (SART) allows to identify both object geometry and α-Lactose filling.

© 2015 Optical Society of America

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