Applications in broadband THz spectroscopy towards material studies

Türkşen, Zeynep
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> ZnTe crystal for detection had a bandwidth up to 1 THz with a 1000:1 signal to noise ratio (S/N). Using this system, various materials were investigated to study the usefulness of the obtained bandwidth. Absorption coefficient and refractive indices of the sample materials were calculated. Results showed that the bandwidth of the system was not sufficient to obtain fingerprint properties of these materials. In order to improve the system, optical rectification method was used for THz generation. A different THz-TDS system was built with a 1mm thick <110> ZnTe crystal used for the method of non-linear generation of THz radiation. Theoretical calculations of radiated intensity and electric field were done to analyze the expected bandwidth of the system. Results showed that the generation and the detection crystal thicknesses affect the obtained bandwidth of the system in that the bandwidth limiting factor is the crystal thickness and not the ultrafast laser pulse duration. Especially for detection, measurements obtained with both a 1mm thick and 2mm thick <110> ZnTe crystal showed that there was not much difference in bandwidth as was predicted by theory. Also in order to increase the signal to noise ratio, the optics used in the system were optimized. It was found that by using same focal lengths for focusing and collimating optics around the generation crystal and by using a short focal length parabolic mirror, S/N could be improved. After these improvements this THz-TDS system which uses optical rectification for THz generation and electro-optic method for THz detection had a larger bandwidth up to 3 THz but with a lower 100:1 signal to noise ratio.


Use of a simple transient extension chamber with ETV-ICPMS: quantitative analysis and matrix effects
Ertaş, Gülay (Royal Society of Chemistry (RSC), 2003-01-01)
The transient extension (TEx) chamber was developed to provide a simple means of lengthening an electrothermal vaporizer (ETV) signal for the purpose of obtaining a full mass scan from a single ETV firing with inductively coupled plasma mass spectrometry (ICPMS) detection. The TEx chamber was used for quantitative analysis of natural water (NIST SRM 1640). Quantitative analysis was done for Co, Be, Pb, Sb and Cd. Detection limits for the five elements tested with the TEx chamber were in the 1-10 mug L-1 ran...
Broadband THz Modulators Based on Multilayer Graphene on PVC
KAYA, Emine; Kakenov, Nurbek; Kocabas, Coskun; Altan, Hakan; Esentürk, Okan (2016-09-30)
In this study we present the direct terahertz timedomain spectroscopic measurement of CVD-grown multilayer graphene (MLG) on PVC substrate with an electrically tunable Fermi level. In a configuration consisting MLG and injected organic dopant, the transmitted intensity loss of terahertz radiation was observed with an applied voltage between 0 and 3.5 V.We showed that MLG on PVC devices provided approximately 100 % modulation between 0.2 and 1.5 THz at preferentially low operation voltage of ca. 3V. The obse...
Gravitational waves and gravitational memory
Korkmaz, Ali; Tekin, Bayram; Department of Physics (2018)
We study the gravitational waves produced by compact binary systems in the linear regime of massless general relativity and calculate the gravitational memory produced by these waves on a detector.
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...
Some properties and conserved quantities of the short pulse equation
Erbaş, Kadir Can; Karasu, Emine Ayşe; Department of Physics (2008)
Short Pulse equation derived by Schafer and Wayne is a nonlinear partial differential equation that describes ultra short laser propagation in a dispersive optical medium such as optical fibers. Some properties of this equation e.g. traveling wave solution and its soliton structure and some of its conserved quantities were investigated. Conserved quantities were obtained by mass conservation law, lax pair method and transformation between Sine-Gordon and short pulse equation. As a result, loop soliton chara...
Citation Formats
Z. Türkşen, “Applications in broadband THz spectroscopy towards material studies,” M.S. - Master of Science, Middle East Technical University, 2011.