Pulsed three dimensional THZ imaging

Karagöz, Burcu
In this thesis, a Terahertz Pulsed Imaging (TPI) system based on Terahertz Time Domain Spectroscopy (THz-TDS) was constructed to non-destructively evaluate and image samples. By scanning samples in the time domain, three dimensional (3D) views of sample geometries were generated. In order to image samples in 3D, a THz-TDS system based on reflection mode which permits the scanning of samples across THz beam was constructed. Thus, third axis which characterizes the depth profile of samples was obtained. THz pulse was focused on samples with an angle of incidence of 34° to a measured spot diameter of 3 mm. In the system, InGaAs based photoconductive antennas (PCAs) were used for THz generation and detection and a bandwidth up to 1 THz was obtained. Terahertz images of two different types of samples were presented to examine the constructed THz imaging system. The first sample was composed of acetate layers and letters cut from aluminium foil which were placed at various cross sections in depth. The second sample type was tooth slices of thickness ~ 1 mm sectioned mesiodistally in parallel. These tooth samples were prepared by the Faculty of Dentistry of Ankara University in Ankara, Turkey. By using this system, 3D images of the layered sample could be extracted by performing a time domain analysis although THz images were obtained from raw THz data. It has also been shown that THz imaging can be used to detect and monitor dental caries.


Terahertz time-domain spectroscopy and its application towards measurements in biology
Özer, Zeynep; Altan, Hakan; Department of Physics (2016)
Terahertz Time-Domain Spectroscopy (THz-TDS) has proved to be an exceptional tool in measurements of biological and non-biological materials. The main reason why this method is preferred is that terahertz waves are typically harmless on samples due to the low excitation energy. Furthermore, one is able to extract parameters such as the absorption and refractive index easily directly from the data without using modeling. The low energy of the terahertz wave also makes it a useful tool for characterizing dyna...
Applications in broadband THz spectroscopy towards material studies
Türkşen, Zeynep; Altan, Hakan; Department of Physics (2011)
The purpose of this work was to construct and analyze a THz time domain spectroscopy (THz-TDS) system by using a nanojoule energy per pulse ultrafast laser (non-amplified ultrafast laser or oscillator) source and a non-linear optical generation method for THz generation. First a THz-TDS system, which uses photoconductive antenna (PCA) method for THz generation, was built to understand the working principles of these types of systems. This THz-TDS system which used PCA for generation and a 2mm thick <110> Zn...
Image Reconstruction and Optimization Using a Terahertz Scanned Imaging System
Yildirim, Ihsan Ozan; ÖZKAN, VEDAT ALİ; Idikut, Firat; Takan, Taylan; ŞAHİN, ASAF BEHZAT; Altan, Hakan (2014-09-23)
Due to the limited number of array detection architectures in the millimeter wave to terahertz region of the electromagnetic spectrum, imaging schemes with scan architectures are typically employed. In these con fi gurations the interplay between the frequencies used to illuminate the scene and the optics used play an important role in the quality of the formed image. Using a multiplied Schottky-diode based terahertz transceiver operating at 340 GHz, in a stand-o ff detection scheme; the e ff ect of image q...
Bezek, Can Deniz; Öktem, Sevinç Figen; Department of Electrical and Electronics Engineering (2021-9-08)
Computational imaging is the process of forming images from indirect measurements using computation. In this thesis, we develop deep learning-based unrolled reconstruction methods for various computational imaging modalities. Firstly, we develop two deep learning-based reconstruction methods for diffractive multi-spectral imaging. The first approach is based on plug-and-play regularization with deep denoisers whereas the second one is an end-to-end learned reconstruction based on unrolling. Secondly, we con...
Modeling of dispersion in a polymeric chromatographic monolith
Koku, Harun; Schure, Mark R.; Lenhoff, Abraham M. (Elsevier BV, 2012-05-11)
Dispersion in a commercial polymeric monolith was simulated on a sample geometry obtained by direct imaging using high-resolution electron microscopy. A parallelized random walk algorithm, implemented using a velocity field obtained previously by the lattice-Boltzmann method, was used to model mass transfer. Both point particles and probes of finite size were studied. Dispersion simulations with point particles using periodic boundaries resulted in plate heights that varied almost linearly with flow rate, a...
Citation Formats
B. Karagöz, “Pulsed three dimensional THZ imaging,” M.S. - Master of Science, Middle East Technical University, 2016.