Time Domain Terahertz Attenuated Total Internal Reflection Spectroscopy

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A. Atalar M.Sc. Thesis ATR Spectroscopy.pdf

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2021-7

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Atalar, Ataberk

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In this thesis, a Terahertz Time Domain Spectroscopy system based on the Attenuated Total Internal Reflection principle (THz ATR-TDS) was constructed in order to non-destructively evaluate materials which show high absorptive characteristics at THz frequencies and therefore prove other widely used THz transmission spectroscopy methods ineffective. The response of the system without a sample differs in amplitude and in time scale when compared to a sample measurement due to the real and imaginary parts of the refractive index of the samples. Through an analysis of the interaction of the THz field with the sample and signal processing in the time and frequency domain, optical properties of samples in the THz frequency range were obtained. THz signal was generated and detected by two InGaAs based photoconductive antennas (PCA) and a bandwidth up to 1 THz was obtained. Generated THz beam was guided by off-axis parabolic mirrors and then focused inside a Si (Silicon) prism to reflect internally at the base with an incidence angle of 51.6 according to the total internal reflection (TIR) principle. The diameter of the focal point at this surface was measured to be 4 mm. Measurements of water which has exceptionally high absorption in THz region of electromagnetic spectrum were presented in order to assess the effectiveness of the constructed spectroscopy system. In addition, mouth tissue samples with different types of lesions prepared by the Faculty of Dentistry of Ankara University in Ankara, Turkey were investigated to determine the efficiency of the THz ATR-TDS technique in analysis of biological samples which contain a high amount of water. It has been shown that by using this system, high absorptive materials such as water and other various water containing samples could be optically characterized at THz frequencies through time and frequency domain analysis.

Subject Keywords

Terahertz Time Domain Spectroscopy, Therahertz ATR Spectroscopy, Attenuated Total Internal Reflection, Total Internal Reflection

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https://hdl.handle.net/11511/91655

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

A. Atalar, “Time Domain Terahertz Attenuated Total Internal Reflection Spectroscopy,” M.S. - Master of Science, Middle East Technical University, 2021.