Time Domain Terahertz Attenuated Total Internal Reflection Spectroscopy

Atalar, Ataberk
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.


Gelgeç, Melis; Altan, Hakan; Department of Physics (2022-8-25)
In this thesis, a Terahertz Attenuated Total Reflection Time Domain Spectroscopy (THz ATR-TDS) system was constructed to measure biological media. The constructed system driven by a Yb:doped mode-locked fiber laser had a limited bandwidth of about 0.3 THz. This bandwidth limited the analysis of various samples in the frequency domain. To overcome this limitation a method was developed so that the samples can be analyzed in the time-domain. Oral soft tissue samples collected were used in order to demonstrate...
Terahertz Transmission Through Patterened Vanadium Oxide Thin Films on Dielectric Substrates
AKKAYA, MAHİNUR; Demirhan, Y.; Yuce, H.; Aygun, G.; Ozyuzer, L.; SABAH, CUMALİ; Altan, Hakan (SCITEPRESS, AV D MANUELL, 27A 2 ESQ, SETUBAL, 2910-595, PORTUGAL; 2017-03-01)
Patterned and unpatterned films of vanadium oxide grown on dielectric substrates such as fused silica and sapphire were grown and analysed by varying the temperature using terahertz time domain spectroscopy. After investigating the critical transition temperature near 340K, a well-known cross-shaped pattern was studied to observe any resonances upon transmission. Due to the poor conductivity of the films the frequency selective nature of the structure was not observed, however an etalon effect could be seen...
Escape of photoelectrons and Compton-scattered photons from an HPGe detector
Can, Cüneyt (Wiley, 2003-07-01)
The response function of a planar HPGe detector due to escape of photoelectrons and Compton-scattered photons was studied for a point source with 59.5 keV energy. It was shown that both mechanisms, in addition to Ge x-ray escape, leading to partial deposition of energy, could be observed in the same experiment. A Monte Carlo program was used to investigate these components of the response function. The results indicate that although the escape of scattered photons and Ge x-rays are of the same magnitude, th...
Photoelectron, compton and characteristic x-ray escape from an HPGe detector in the range 8-52 keV
Yilmaz, E; Can, Cüneyt (Wiley, 2004-11-01)
Escape of photoelectrons, Compton-scattered photons and Ge x-rays from an HPGe detector was studied as a function of energy in the range 8-52 keV. A variable-energy source producing Cu, Rb, Mo, Ag, Ba. and Tb x-rays was used. All three mechanisms for energy loss were observed in the same experiment for Ba and Tb, while only x-ray and photoelectron escapes were evident in the spectra for Ag, Mo, Rb, and Cu. Spectral features and possible mechanisms for partial energy deposition were investigated. A Monte Car...
Optical absorption of a quantum well with an adjustable asymmetry
Yildirim, H.; Tomak, Mehmet (Springer Science and Business Media LLC, 2006-04-01)
The effects of asymmetry and the electric field on the electronic subbands and the nonlinear intersubband optical absorption of GaAs quantum wells represented by a Poschl-Teller confining potential are studied. The potential itself can be made asymmetric through a correct choice of its parameter set and this adjustable asymmetry is important for optimizing the absorption. In that way optimal cases can be created. We calculate the modified wave functions and electronic subbands variationally. The linear and ...
Citation Formats
A. Atalar, “Time Domain Terahertz Attenuated Total Internal Reflection Spectroscopy,” M.S. - Master of Science, Middle East Technical University, 2021.