Image reconstruction based on active scan techniques in the terahertz frequency range

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Edebiyat Fakültesi, Fizik Bölümü, Türkiye

Tezin Onay Tarihi: 2014

Öğrenci: VEDAT ALİ ÖZKAN

Danışman: HAKAN ALTAN

Özet:

THz continuous wave (CW) imaging systems have attracted interest in the past decade since they have the ability to detect non-metal threats such as ceramic knives. Moreover due to low energy levels of THz signals, these systems are not harmful. Although various types of imaging systems have been developed, the nature of THz waves has prevented the scienti c community from producing a fast, high resolution and cost e ective imaging system. In this study we have investigated both experimentally and theoretically the application THz waves in various imaging system con gurations. The main goal was to understand the e ects of the optical system design as well as noise and other parameters that could impact the formation of images in an active THz imager based on frequencies near 340GHz. The designed optical system was simulated and the e ects of scanning the target eld were assessed in the simulated images of various targets. The results show that reliable target detection will be aided by post-processing the images using various techniques. Furthermore, to experimentally demonstrate an active imaging system, compressive sensing was used in a non-scanning re ection based optical geometry. In these experiments a mm-wave source near 120GHz was used to obtain the images. The obtained images were analysed and compared to that of simulations. The results show that compressive sensing methods can be implemented successfully to improve image acquisition in typically low-resolution THz imaging systems. Finally, the e ect of imaging in the terahertz frequency range was also investigated for passive imaging methods. A commercial system working in the mm-wave range was used to obtain raw images at stand-o distances. The goal was to process the images without using the routines supplied by the manufacturer. Using wellestablished routines these raw images were processed successfully. Throughout this study careful attention is paid on the limitations on speed and resolution of these imaging systems and discussions on the applicability of the methods developed within this thesis are discussed throughout.