Novel methods in modulation and detection of terahertz waves for imaging applications

Takan, Taylan
Terahertz radiation, due to its unique properties offers a plethora of possibilities of applications in various domains including security & defense, communications, material characterization, product inspection and medical imaging. In all these fields, cost-effective, high-resolution, and high-speed terahertz imaging is a greatly desired technology. However due the inherent challenges associated with terahertz detection, building a terahertz imaging system that satisfies all these requirements necessitates the development of novel detectors, components, and imaging methods. In this thesis, we present the work done to advance terahertz detectors, modulators and imaging methods, towards the aim of developing a cost-effective, high-resolution, and high-speed terahertz imaging system. For the cost-effective detection of terahertz radiation, we investigate the use of neon indicator lamps as glow discharge detectors and achieve response comparable to commercially available high-cost detectors. Using a Schottky diode multiplied source and lock-in techniques behavior of glow discharge detectors up to 90 kHz modulation is investigated in the range from 0.260 THz to 0.380 THz. Besides, polarization sensitivity and transmittance of these detectors are also measured in this range. Overall, results obtained from these investigations suggest up to a twofold increase in detected signal as the modulation frequency increases from 1 kHz to 90 kHz. Furthermore, the measurements show that internal geometry of these detectors influences their interaction with terahertz radiation significantly and certain types of indicator lamps perform much better. For spatial modulation of terahertz waves, devices utilizing graphene and vanadium dioxide are characterized. Also, the coupling of metamaterials and frequency selective surfaces to these devices are studied. We present the experimental results for a graphene-based tunable THz cavity that provides %98 modulation at 0.370 THz. Also, a graphene-based spatial light modulator, capable of enabling broadband modulation of THz waves with voltage controlled patterns is investigated. Besides, we achieved frequency selectivity in the spatial light modulator by coupling it to frequency selective surfaces and metamaterials. Furthermore, a vanadium dioxide based metamaterial is shown experimentally to have frequency selectivity and temperature controlled transmissivity. Finally, we give experimental results of four different terahertz imaging systems which were set up to see objects hidden behind and inside walls and other visibly opaque obstructions. We show more than two times increase in speed compared to conventional pixel scanning methods, through the use of compressed sensing. Besides, we present a novel superimposed spatial light modulator that enables up to ten times reduction in size and increase in speed. Furthermore, by using the graphene-based spatial light modulator, we demonstrate an electrically controlled terahertz imaging system.


Terahertz (>0.3THz) active imaging systems
İdikut, Fırat; Altan, Hakan; Department of Physics (2016)
Imaging systems based on terahertz waves are becoming an integral part of commercial and military screening applications. In this thesis, the prototype of active scan THz imaging system was constructed for detection of concealed objects at standoff distance longer than 5m. The system was mounted on a platform that can adjust in height, tilt and azimuthal angle. The methods of generation and detection of THz signal are based on Schottky diode rectifiers and Schottky diode mixers. The wavelength of the contin...
Synthesis of Monitoring Rules with STL
Aydin, Sertac Kagan; Aydın Göl, Ebru (World Scientific Pub Co Pte Lt, 2020-09-01)
Online monitoring is essential to enhance the reliability for various systems including cyber-physical systems and Web services. During online monitoring, the system traces are checked against monitoring rules in real time to detect deviations from normal behaviors. In general, the rules are defined as boundary conditions by the experts of the monitored system. This work studies the problem of synthesizing online monitoring rules in the form of temporal logic formulas in an automated way. The monitoring rul...
Optimal design of sparse mimo arrays for wideband near-field imaging based on a statistical framework
Kocamış, Mehmet Burak; Öktem, Sevinç Figen; Department of Electrical and Electronics Engineering (2018)
Wideband near-field imaging is an emerging remote sensing technique in various applications such as airport security, surveillance, medical diagnosis, and through-wall imaging. Recently, there has been increasing interest in using sparse multiple-input-multiple-output (MIMO) arrays to achieve high resolution with reduced hardware complexity and cost. In this thesis, based on a statistical framework, an optimal design method is presented for two-dimensional MIMO arrays in wideband near-field imaging. Differe...
Pulsed three dimensional THZ imaging
Karagöz, Burcu; Altan, Hakan; Department of Physics (2016)
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 p...
Computational Spectral Imaging with Photon Sieves
Öktem, Sevinç Figen; Davila, Joseph M. (2016-01-01)
Spectral imaging, the sensing of spatial information as a function of wavelength, is a widely used diagnostic technique in diverse fields such as physics, chemistry, biology, medicine, astronomy, and remote sensing. In this paper, we present a novel computational imaging modality that enables high-resolution spectral imaging by distributing the imaging task between a photon sieve system and a computer. The photon sieve system, coupled with a moving detector, provides measurements from multiple planes. Then ...
Citation Formats
T. Takan, “Novel methods in modulation and detection of terahertz waves for imaging applications,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.