Terahertz bölgesi için metamalzeme dizaynı ve karakterizasyonu.

Metamaterials are manmade structures whose electromagnetic properties can be controlled with subwavelength inclusions. Due to this property metamaterials has gained importance in the terahertz region. Although terahertz radiation has many important applications in communication, astronomy, spectroscopy, imaging, biology and sensing, lack of materials which gives a response in this range decelerated development of devices to control and manipulate the terahertz waves. Metamaterials show a large potential to ll this gap since they have many applications such as superlenses, terahertz modulators, and antenna structures. Metamaterials are unique in that they exhibit a negative magnetic permeability and dielectric permittivity. Two dimensional metamaterials are called metasurfaces. These are two dimensional arti cial structures which show single negative metamaterial properties as opposed to three dimensional structures which show double negative properties. In this thesis, metasurface structures based on various conducting materials such v as copper, gold, indium tin oxide as well as yttrium barium copper oxide were designed, simulated and characterized especially for the terahertz region of the electromagnetic spectrum. Emphasis was placed on highly conducting materials, such as metals and superconductors. Extracted data of substrates were used to simulate metasurface structures using commercially obtained Computer Simulation Technology (CST) Microwave Studio program. Each metasurface structure was designed such that the frequency of the resonance lies in the terahertz region and this was veri ed by simulating the behavior of the structure in the terahertz region. Superconducting metasurface characterization was done with a closed cycle helium cryostat that was installed inside the terahertz time domain spectroscopy system. Experiments were done at 20, 40, 60, 70, 80, 84, 86, 90 and 298K. At di erent temperatures a shift in the resonance frequency and change in the resonance amplitude was observed. It was found that the simulation results were in good agreement with terahertz time domain spectroscopy results. The ability to measure both amplitude and phase allows this technique, terahertz time spectroscopy, to be used to extract metamaterial properties without prior knowledge of the structure shape. M.S. - Master of Scienc

High Photosensitized Singlet Oxygen Generating Zinc and Chloroindium Phthalocyanines Bearing (4-isopropylbenzyl)oxy Groups as Potential Agents for Photophysicochemical Applications

In this study, novel phthalonitrile derivatives (1 and 2) and their peripherally and non-peripherally tetra (4-isopropylbenzyl)oxy-substituted zinc and chloroindium phthalocyanine complexes (3-6) have been prepared for the first time. The synthesized phthalonitrile derivatives and phthalocyanine complexes were characterized spectroscopically. Not only the chloroindium phthalocyanines but also zinc phthalocyanines are essentially free from aggregation in THF at the studied micromolar concentration. The purpose is to compare the effects of two types of substitution on the phthalocyanines to be used as sensitizers in photodynamic therapy (PDT). Photophysical and photochemical properties of all phthalocyanines are investigated and the results showed that the peripheral phthalocyanines more effectively photooxidize DPBF through singlet oxygen. The photochemical results showed that both ZnPc (3 and 5) and InPc (4 and 6) can be used as sensitizers in PDT because of their very high singlet oxygen quantum yields (range from 0.80 to 0.97)

Fiber Lazerle Bütünleşik Terahertz Spektrometre

Elektromanyetik ışık tayfının 100 GHz (λ=3 mm) ve 10 THz (λ=30 μm) aralığına denk düşen terahertz bölgesi, benzersiz bilgiler içerdiği için bilim insanlarının ilgisini çekmektedir. Öte yandan, THz frekanslarının üretiminde elektronik ve optik yöntemlerin aynı anda kullanılması gerektiğinden, ışık tayfının optik ve elektronik bölgelerinde gerçekleşen gelişmeleri aynı oranda THz bölgesinde görememekteyiz. Günümüze kadar geliştirilen teknikler hassas ve her aşamasında optimizasyon gerektiren karmaşık sistemlerdir.Bu projede THz spektroskopi ölçümlerin sinyal/gürültü oranının iyileştirilmesi ile bahsedilen üç çalışmada da kazanç sağlanması hedeflenmektedir. Hedeflenen bu amaç için laboratuvarda kullanılan THz spektrometrenin, THz sistem kutusu ile çevresel etkilerden izole edilmesi gerekmektedir. Üretilen THz ışınlarının, polar yapı özelliğine havadaki nemle etkileşimini azaltmak içinse sistem kutusu içerisinin azot gazı ile doldurulması hedeflenmektedir. Daha sonra THz üretiminde kullanılan FIA yapılar üzerine lazer ışınlarının daha iyi odaklanabildiğinden emin olmak için, bu yapılar üzerinden mevcut yöntem olan direnç değeri okumak yerine, daha verimli doğru bir yöntem olan akım değerini okumak için çok hassas multimetre alımı hedeflenmektedir. Sistem optimizasyonu tamamlandıktan sonra THz spektroskopi ölçümlerinde elde edilen veriler, veri toplama kartı ile bir bilgisayara aktarılacak ve analiz edilecektir. Böylelikle laboratuvarımızda yürütülen üç çalışmaya da kazanç sağlan

Extraction of dielectric and magnetic material properties for a periodic hole array THz filter

With the increase in optical applications in the terahertz frequency range there is a greater need for devices that work at these frequencies. One such device which has applications which range from spectroscopy to imaging is the band pass filter. The frequency selective nature of this component can be used for filtering noise during signal processing or can be even used for reducing radiation background levels for imaging purposes [1, 2]. The simplest form of this filter structure has been shown to be that of a free-standing metal sheet with a hole array. The frequency selective nature of the filter is realized by changing the structural parameters of the hole array with respect to the propagating input THz wave. Due to the sub-millimeter wave nature of the radiation the patterns are easier to fabricate for low frequency terahertz radiation applications (<1THz). Here, by using a high power Yb:doped pulsed nanosecond fiber laser system with exceptional beam quality, aluminum metal surfaces were machined with high precision leading to a high quality band pass filter that was shown to work in the terahertz frequency range [3]. We modeled the THz transmission through the the structure that was produced using FDTD simulation tools and also characterized them using the existing home-built time-domain terahertz spectrometers in our laboratories. Results of FDTD simulations are found to be consistent with transmission coefficient which is obtained from the experiment. In order to understand the efficiency of the composite structure which can be described as a frequency selective surface, the electrical permittivity (ε) and magnetic permeability (μ) is extracted from the transmission and reflection simulations [4]. The significance of these values is discussed with respect to the width and transmission observed for the fabricated and measured filter

Phthalocyanines with bromobenzenesulfanyl substituents at non-peripheral position: Preparation, photophysical and photochemical properties

Electron-donating bromobenzenesulfanyl-group-substituted phthalonitrile derivative (1) and its novel non-peripherally tetra-substituted metal-free, indium and zinc phthalocyanine complexes (2-4) have been prepared for the first time. The chemical structures of this new phthalonitrile and its phthalocyanine derivatives were characterized by UV-vis, FT-IR, NMR, and MALDI-TOF mass spectrometry. The introduction of this electron-donating sulfanyl type of non-peripheral substituent accounts for a remarkable red shift of the phthalocyanine Q band to approximately 730 nm. Photophysical and photochemical properties of the novel functional complexes were also examined as photosensitizers for PDT applications

Sensör Uygulamaları İçin THz Metamalzeme Yapıların Geliştirilmesi

Terahertz teknolojisinde metamalzemeler, doğal malzemelerden elde edilemeyen elektromanyetik özellikler gösterdiği ve istenen fonksiyonellikte tasarlanabildiğinden, yapay optik elemanların tasarımında önemli bir yere sahiptir. Son yıllarda elektromanyetik spektrumunun farklı frekanslarında çeşitli uygulamalar için metamalzeme alanında çok fazla araştırma yapılmış ve bu çalışmalar büyük ilgi görmüştür. Metamalzemeler geometrik olarak ölçeklendirilebilirler ve böylece radyo, mikrodalga, milimetre-dalga, uzak infrared (IR), orta-IR, yakın IR frekanslarını ve hatta görünür dalga boylarını kapsayan geniş bir frekans aralığında çalışabilirler. Analitik, nümerik ve deneysel yaklaşımlarla, özgün metamalzeme etkilerini araştıran birçok bilimsel çalışma başlamıştır. Metamalzemelerin farklı terahertz frekanslarında gösterdikleri rezonant etkiler özellikle detektör ve spektroskopik yöntemler açısından son derece önemli bir yer edinmeye başlamıştır. Bununla beraber ODTU KKK Elektrik ve Elektronik Mühendisliği Bölümünde öğreim üyesi olan Doç. Dr. Cumali Sabah ile birlikte geliştirdiğimiz metamalzeme çalışmaları terahertz dalga boylarında yeni bir teknoloji geliştirme alanı yaratmıştır. Kendisi THz metamalzeme yapıların tasarlanması ve modellenmesi konularında yetkindir, bizim grup ise daha çok bu malzemelerin karakterizasyonu ve deneysel analizi üzerine çalışmalarını yoğunlaşmıştır. Bu iki çalışma grubun konularının doğal birleşimi sayesinde terahertz teknolojileri için beraber yüksek

An Indium Tin Oxide Metamaterial Filter for the Terahertz regime Design Fabrication and Characterization

Metamaterials are novel structures that show unique optical properties and promise applications such as perfect lenses, filters, invisibility cloaks and antennas [1, 2]. Various metamaterial structures with different metals and semi-conductors have been investigated to date [3, 4]. In this study, fishnet structures based on indium tin oxide (ITO) patterned on quartz substrates are investigated in the terahertz region. ITO thin films form an integral part of various optoelectronic devices [5]. Their use as electromagnetic filters is expected to gain importance as interest in developing terahertz range wireless data transfer architectures develops. The structure consists of a sub-micron thick ITO thin film patterned on a quartz crystal substrate. The transmission of THz radiation is analyzed with respect to the dimensions of the pattern. ITO conductivity is on the order of 100 times less than as in gold, which decreases resonant effects observed through various patterns. Using FDTD simulation, not only did we observe a diminished resonance but it was also shifted towards the low frequency THz range for as compared to the same pattern simulated as a perfect conductor. The validity of the simulations are compared to fabricated structures characterized by both our home-built terahertz time domain spectroscopy (THz-TDS) systems and continuous wave tunable THz systems

Terahertz Bandpass Frequency Selective Surfaces on Glass Substrates Using a Wet Micromachining Process

This paper presents terahertz (THz) frequency selective surfaces (FSS) implemented on glass substrate using standard microfabrication techniques. These FSS structures are designed for frequencies around 0.8 THz. A fabrication process is proposed where a 100-mu m-thick glass substrate is formed through the HF etching of a standard 500-mu m-thick low cost glass wafer. Using this fabrication process, three separate robust designs consisting of single-layer FSS are investigated using high-frequency structural simulator (HFSS). Based on the simulation results, the first design consists of a circular ring slot in a square metallic structure on top of a 100-mu m-thick Pyrex glass substrate with 70% transmission bandwidth of approximately 0.07 THz, which remains nearly constant till 30A degrees angle of incidence. The second design consists of a tripole structure on top of a 100-mu m-thick Pyrex glass substrate with 65% transmission bandwidth of 0.035 THz, which remains nearly constant till 30A degrees angle of incidence. The third structure consists of a triangular ring slot in a square metal on top of a 100-mu m-thick Pyrex glass substrate with 70% transmission bandwidth of 0.051 THz, which remains nearly constant up to 20A degrees angle of incidence. These designs show that the reflections from samples can be reduced compared to the conventional sample holders used in THz spectroscopy applications, by using single layer FSS structures manufactured through a relatively simple fabrication process. Practically, these structures are achieved on a fabricated 285-mu m-thick glass substrate. Taking into account the losses and discrepancies in the substrate thickness, the measured results are in good agreement with the electromagnetic simulations

An indium tin oxide metasurface filter for terahertz applications: Design, fabrication, and characterization

In this paper, using a cross-shaped complementary Indium Tin Oxide (ITO)-based metasurface design, the transmission of THz radiation is shown to be filtered within the 3 dB level from maximum in the frequency range of interest (333 GHz). Various metasurface structures primarily composed of cross-shaped openings with a 400 micron unit cell size are patterned on top of 1750 micron thick fused silica substrates. They are patterned using UV lithography methods after the films were grown using DC sputtering. The fabricated structures were characterized using Terahertz Time Domain Spectroscopy (THz-TDS) measurement technique. The measured transmission agrees well with the simulation of the structure for four different samples with different geometries. These results suggest that metasurface and/or metamaterial patterns based on ITO in visibly transparent media can be utilized for filtering of frequencies in the long wavelength spectrum. These types of filters can be very useful in the near future for THz communication and security applications. ©Scientific and Technological Research Council of Turkey TUBITAK (114F091); Middle East Technical University-Northern Cyprus Campus (METU-NCC) Grant BAP-FEN-16-K-8; BAGEP Award of the Science Academy in Turke