Physical Sciences and Mathematics Commons^™

Fabrication Of Black Phosphorus Terahertz Photoconductive Antennas, Nathan Tanner Sawyers

Physics Undergraduate Honors Theses

Terahertz (THz) photoconductive antennas (PCAs) using 40nm thin-film flakes of black phosphorus (BP) and hexagonal boron nitride (hBN) have been shown computationally to be capable of THz emission comparable to those based on GaAs [2]. In this paper, I briefly describe the scientific and practical interest in THz emissions and explain what warrants research into black phosphorus as a photoconductive semiconductor in THz devices. Furthermore, I outline the basic principle of how these antennas work and mention alternative designs produced by other researchers in the past. Finally, I summarize the fabrication process of these antennas, as well as the measurements …

Nondestructive Evaluation Of 3d Printed, Extruded, And Natural Polymer Structures Using Terahertz Spectroscopy And Imaging, Alexander T. Clark

Dissertations

Terahertz (THz) spectroscopy and imaging are considered for the nondestructive evaluation (NDE) of various three-dimensional (3D) printed, extruded, and natural polymer structures. THz radiation is the prime candidate for many NDE challenges due to the added benefits of safety, increased contrast and depth resolution, and optical characteristic visualization when compared to other techniques. THz imaging, using a wide bandwidth pulse-based system, can evaluate the external and internal structure of most nonconductive and nonpolar materials without any permanent effects. NDE images can be created based on THz pulse attributes or a material’s spectroscopic characteristics such as refractive index, attenuation coefficient, or …

The Effects Of An Ultrafast Pulsed Laser On Ybco Thin Film Circuit Transients, Matthew L. Rustad

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Terahertz (THz) frequency light has shown promise for a wide variety of applications due to its material characterization and imaging capabilities. Its nondestructive nature coupled with its submillimeter spatial resolution provides the most value for terahertz light as an imaging tool. The application of terahertz technology has been limited by a lack of novel and powerful sources. It has been shown that that Yttrium Barium Copper Oxide (YBCO), a type II superconductor, has certain properties that would allow YBCO to be an effective source for THz light. Recent microwave work has shown that when a persistent supercurrent is placed on …

Computational Modeling Of Black Phosphorus Terahertz Photoconductive Antennas Using Comsol Multiphysics With Experimental Comparison Against A Commercial Lt-Gaas Emitter, Jose Isaac Santos Batista

Graduate Theses and Dissertations

This thesis presents computational models of terahertz (THz) photoconductive antenna (PCA) emitter using COMSOL Multiphysics commercial package. A comparison of the computer simulated radiated THz signal against that of an experimentally measured signal of commercial reference LT-GaAs emitter is presented. The two-dimensional model (2D) aimed at calculating the photoconductivity of a black phosphorus (BP) PCA at two laser wavelengths of 780 nm and 1560 nm. The 2D model was applied to the BP PCA emitter and the LT-GaAs devices to compare their simulated performance in terms of the photocurrent and radiated THz signal pulse. The results showed better performance of …

Characterization Of A Novel Terahertz Chemical Sensor, Daniel J. Tyree

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A recently constructed novel analytical tabletop terahertz (THz) chemical sensor capable of detecting a wide range of gases with high sensitivity and specificity was characterized to assess its performance over a range of operational parameters. The sensor was designed with an objective of quantifying composition of exhaled human breath, where target concentrations span part per trillion (ppt) to part per billion (ppb) level of dilutions. The sensor utilizes terahertz rotational spectroscopy of sampled gases for quantification of dilutions. The sensor occupies a volume of ~ 2 ft3 and incorporates a coiled absorption cell, thermal desorption tubes, and all necessary electronic …

Investigation Of Phonon Polaritons In An Hbn Gan Heterostructure, Catherine G. O'Hearn

Graduate Theses, Dissertations, and Problem Reports

There have been many great advances in the generation and manipulation of optics in the visible and near infrared (IR) range over the past decade. This is largely due to plasmonic enhancement, which has led to new technology in biosensing and molecule detection, solid-state lighting, and solar energy harvesting. The field of plasmonics uses quanta of plasma oscillations, plasmons, formed from the interaction between electromagnetic radiation and free electrons to enhance optical near field magnitudes. However, there is still a large region of the electromagnetic spectrum, covering the mid-infrared (MIR) and terahertz (THz) regions, ranging from 3 μm to 1 …

Power Distribution Of Terahertz Emission From Hexagonal Bscco Microstrip Antennas, Andrew E. Davis

Honors Undergraduate Theses

We analyze the distribution of coherent terahertz radiation from a regular hexagonal microstrip antenna (MSA) made from the high-T_c superconductor Bi₂Sr₂CaCu₂O_8+x (BSCCO). We discuss the C_6v symmetry of the solutions of the wave equation on a hexagonal domain and distinguish between the closed-form and non-closed-form solutions. The closed-form wavefunctions of the transverse magnetic (TM) electromagnetic cavity modes are presented and formulas for the radiated power arising from the uniform part of the AC Josephson current and from the resonant cavity modes are derived. The wavefunctions and angular distribution of radiation from …

Extraordinary Optical Transmission In Aligned Carbon Nanotube Devices At Terahertz Frequencies., Shaikhah F. Almousa

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In the phenomenon known as extraordinary optical transmission (EOT), a narrow band of selected frequencies are transmitted when incident on an array of subwavelength periodic apertures where the resonant frequency is determined by the geometry of the array of apertures and optical properties of the metal-dielectric interface. This takes place due to the excitation of surface plasmon polaritons (SPPs) at the metal and dielectric interface. Using the COMSOL Multiphysics software RF Module, a unit cell of a carbon nanotube (CNT) based EOT device is modeled in order to verify theoretical calculations of the resonant frequency using S-parameter calculations. The simulation …

Terahertz Molecular Spectroscopy As A Tool For Analytical Probing Of Cellular Metabolism, Mitchell Cameron Paul

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Terahertz spectroscopy has found use as an analytical tool in determining chemical composition of exhaled human breath. This thesis demonstrates a novel application of this technology - analytical sensing of gaseous metabolic products of several types of human cell cultures. An innovative experimental system was developed for probing cellular metabolism using terahertz [THz] rotational spectroscopy. Gaseous emissions of cell cultures were analyzed and compared between several cell types. Cancerous and healthy lung cells as well as cancerous liver cells were studied. This technique carries a lot of promise as a noninvasive method of distinguishing between cell types and identifying cell …

Terahertz Molecular Spectroscopy As A Tool For Analytical Probing Of Cellular Metabolism, Mitchell Cameron Paul

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Terahertz spectroscopy has found use as an analytical tool in determining chemical composition of exhaled human breath. This thesis demonstrates a novel application of this technology - analytical sensing of gaseous metabolic products of several types of human cell cultures. An innovative experimental system was developed for probing cellular metabolism using terahertz [THz] rotational spectroscopy. Gaseous emissions of cell cultures were analyzed and compared between several cell types. Cancerous and healthy lung cells as well as cancerous liver cells were studied. This technique carries a lot of promise as a noninvasive method of distinguishing between cell types and identifying cell …

Terahertz Wireless Communication Through Atmospheric Atmospheric Turbulence And Rain, Jianjun Ma

Dissertations

This dissertation focusses on terahertz (THz) wireless communication technology in different weather conditions. The performance of the communication links is mainly studied under propagation through atmospheric turbulence and rain. However, as real outdoor weather conditions are temporally and spatially varying, it is difficult to obtain reproducible atmospheric conditions to verify results of independent measurements making it a challenge to measure and analyze the impact of outdoor atmospheric weather on communication links. Consequently, dedicated indoor weather chambers are designed to produce controllable weather conditions to emulate the real outdoor weather as closely as possible. To emulate turbulent air conditions, an enclosed …

Terahertz Spectroscopic Breath Analysis As A Viable Analytical Chemical Sensing Technique, Robert M. Schueler

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The ability to quantify trace chemicals in human breath enables the possibility of identifying breath biomarkers to aid in diagnosis. The vast majority of the studies in the analytical breath analysis rely on GC-MS techniques for quantification of the human breath composition1,2,3,4. THz spectroscopy of breath is rapid, sensitive, and highly specific molecular identification in complex mixtures containing 10-100 analytes with near `absolute' specificity. THz spectroscopic breath analyzers require chemical preconcentration. A newly developed custom preconcentrator was constructed and compared in its performance to a commercial system. Unlike the commercial counterpart, the new system does not require cryogenic liquids, is …

High Powered Pulsed Terahertz Light Generation From Superconducting Antenna Arrays, Nicholas C. Padgett

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Terahertz radiation is invaluable for use in spectroscopy and imaging work due to its nondestructive nature. It has become a key focus for those wishing to develop sensors capable of detecting weapons and narcotics unobtrusively and at a distance as well as characterizing materials and identifying defects. An ultrafast pulsed (femtoseconds) laser incident on a superconducting ring has been predicted to cause the emission of terahertz (THz) radiation. It is theorized that the radiation is a result of the supercurrent being modulated by the breaking and recombining of Cooper pairs on the order of picoseconds, where the time scale determines …

Terahertz Radiation From High-Temperature Superconducting Bscco Mesas Of Various Geometries, Daniel P. Cerkoney

HIM 1990-2015

The purpose of this thesis is to examine the radiation from high-temperature superconducting mesas of Bi2Sr2CaCu2O8+ (BSCCO). This is motivated by the need for coherent sources of continuous wave terahertz (THz) emission capable of radiating practically in the THz frequency band. As BSCCO has been shown to be tunable from 0.5–2.4 THz (i.e., through the entire socalled terahertz gap centered about 1 THz), and has a higher peak operating temperature near 1 THz than most alternative sources, it is a good candidate for imaging and spectroscopy device applications [1]. When a static DC voltage is applied to a BSCCO mesa, …

Assessment Of The Applicability Of Terahertz Spectroscopic Breath Sensing Towards Monitoring Type 1 Diabetic Mellitus, Jessica Rose Thomas

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Type 1 diabetes is a condition that cumulatively costs around $14.9 billion in medical expenses every year in the United States. Besides being costly, the monitoring of this disease is invasive, painful, and often embarrassing to the afflicted individual; blood and urine testing is currently the daily method of monitoring blood glucose and ketone levels in the body of type 1 diabetics. Though the use of these samples is standard, another avenue for possibly determining blood glucose has not been completely explored. With over 3000 chemicals reportedly found in exhaled human breath, biomarkers associated with this disorder and many of …

Introducing The Newton-Poisson-Brillouin Model In The Quest For Plasmons In Metallic Carbon Nanotubes, Richard P. Zannoni

Doctoral Dissertations

A new method is presented to model carbon nanotubes (CNT) of micron length. The Newton-Poisson-Brillouin (NPB) model uses Newtonian physics to model the interaction of a population of thermally excited quasi-particles. The NPB model is self-consistent with Poisson’s equation, and the quasi-particles are confined to the CNT’s band structure. In this work, we explore the parameter space of the model.

Multi-Physics Modeling Of Terahertz And Millimeter-Wave Devices, Mohammad Ali Khorrami

Graduate Theses and Dissertations

In recent years, there have been substantial efforts to design and fabricate millimeter-wave and terahertz (THz) active and passive devices. Operation of microwave and photonic devices in THz range is limited due to limited maximum allowable electron velocity at semiconductor materials, and large dimensions of optical structures that prohibit their integration into nano-size packages, respectively. In order to address these issues, the application of surface plasmons (SPs) is mostly suggested to advance plasmonic devices and make this area comparable to photonics or electronics.

In this research, the feasibility of implementing THz and millimeter-wave plasmonic devices inside different material platforms including: …

Development Of Correction Algorithm For Pulsed Terahertz Computed Tomography (Thz-Ct), Suman Mukherjee

Dissertations

For last couple of decades, there has been a considerable improvement in Terahertz (THz) science, technology, and imaging. In particular, the technique of 3-D computed tomography has been adapted to the THz range. However, it has been widely recognized that a fundamental limitation to THz computed tomography imaging is the refractive effects of the sample under study. The finite refractive index of materials in the THz range can severally refract THz beams which probe the internal structure of a sample during the acquisition of tomography data. Refractive effects lead to anomalously high local absorption coefficients in the reconstructed image near …

Analytical Chemical Sensing Using High Resolution Terahertz/Submillimeter Wave Spectroscopy, Benjamin L. Moran

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A highly sensitive and selective Terahertz gas sensor used to analyze a complex mixture of Volatile Organic Compounds (VOCs) has been developed. To best demonstrate analytical capabilities of a THz chemical sensor, we chose to perform analytical quantitative analysis of a certified gas mixture using a prototype gas phase chemical sensor that couples a commercial preconcentration system (Entech 7100A) to a custom high resolution THz spectrometer. A Method TO-14A certified mixture of thirty-nine VOCs was purchased. Twenty-six of the thirty-nine chemicals were identified as suitable for THz spectroscopic detection. The Entech 7100A system is designed and marketed as an inlet …

Characterization Of Ceramic Composite Materials Using Terahertz Non-Destructive Evaluation Techniques, Lindsay Owens

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The characterization of defects such as rust, voids, etc. on materials and the analysis and prediction of strain and stress induced breakdown are well known applications of non-destructive evaluation (NDE) techniques. THz radiation has been suggested as an effective NDE tool for use in the field of ceramics and ceramic matrix composite materials (CMC), via THz spectroscopy and imaging. The goal of this research is to monitor the progression of thermal and mechanical damage applied to the CMC materials using terahertz spectroscopic imaging in order to create a predictive model that will correlate THz imaging data of these materials to …

Terahertz Time Domain Spectroscopy And Fresnel Coefficient Based Predictive Model, Justin C. Wheatcroft

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An optical material parameter predictive model that accounts for sample to air interfaces was developed. The model predicts how a terahertz time-domain spectroscopy time domain pulse will be affected as it passes through a given thickness of a material. The model assumes a homogenous, linear, isotropic dielectric or semiconductor. The inputs to the model are the real and imaginary refractive indices across the desired frequency band. Different dielectric material's optical parameters were taken from the literature and the predicted time domain pulses were shown. It was also shown that the refractive index and absorption coefficient for samples that were optically …

Characterization Of Structured Nanomaterials Using Terahertz Frequency Radiation, Andrew John Niklas

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Measurements that use terahertz frequency radiation to characterize materials are beneficial for scientists trying to determine the physical parameters that govern the interaction of electromagnetic waves and matter at those frequencies. Results will be presented of time domain terahertz spectroscopy measurements taken in forward and backward scattering directions from vertically aligned arrays of multi-walled carbon nanotubes and thin films of perforated copper. The intent of this research is to both corroborate results from independent research groups conducting similar experiments and to further increase understanding in the scientific community with respect to carbon nanotube reflection phenomena at terahertz frequencies.

Optical And Terahertz Energy Concentration On The Nanoscale In Plasmonics, Anastasia Rusina

Physics and Astronomy Dissertations

We introduce an approach to implement full coherent control on nanometer length scales. It is based on spatiotemporal modulation of the surface plasmon polariton (SPP) fields at the thick edge of a nanowedge. The SPP wavepackets propagating toward the sharp edge of this nanowedge are compressed and adiabatically concentrated at a nanofocus, forming an ultrashort pulse of local fields. The profile of the focused waveform as a function of time and one spatial dimension is completely coherently controlled. We establish the principal limits for the nanoconcentration of the terahertz (THz) radiation in metal/dielectric waveguides and determine their optimum shapes required …

Terahertz Response Of Microfluidic-Jetted Fabricated 3d Flexible Metamaterials, Yew Li Hor

Dissertations

Conventional materials exhibit some restrictions on their electromagnetic properties. Especially in terahertz region, for example, materials that exhibit magnetic response are far less common in nature than materials that exhibit electric response. However, materials can be designed, namely artificial man-made metamaterials that exhibit electromagnetic properties that are not found in natural materials by adjusting, for example, the dielectric, magnetic or structural parameters of the constituent elements.

This dissertation demonstrates the use of new fabrication techniques to construct metamaterials in THz range via a material deposition system. The metamaterials are fabricated by stacking alternative layers with conventional designs such as single …

Electrical And Optical Characterization Of Group Iii-V Heterostructures With Emphasis On Terahertz Devices, Aruna Bandara Weerasekara

Physics and Astronomy Dissertations

Electrical and optical characterizations of heterostructures and thin films based on group III-V compound semiconductors are presented. Optical properties of GaMnN thin films grown by Metalorganic Chemical Vapor Deposition (MOCVD) on GaN/Sapphire templates were investigated using IR reflection spectroscopy. Experimental reflection spectra were fitted using a non - linear fitting algorithm, and the high frequency dielectric constant (ε∞), optical phonon frequencies of E1(TO) and E1(LO), and their oscillator strengths (S) and broadening constants (Γ) were obtained for GaMnN thin films with different Mn fraction. The high frequency dielectric constant (ε∞) of InN thin films grown by the high pressure chemical …

Scanning Fabry-Perot Spectrometer For Terahertz And Gigahertz Spectroscopy Using Dielectric Bragg Mirrors, Justin Cleary

Electronic Theses and Dissertations

A scanning Fabry-Perot transmission filter composed of a pair of dielectric mirrors has been demonstrated at millimeter and sub-millimeter wavelengths. The mirrors are formed by alternating quarter-wave optical thicknesses of silicon and air in the usual Bragg configuration. Detailed theoretical considerations are presented for determining the optimum design including factors that affect achievable finesse. Fundamental loss by lattice and free carrier absorption are considered. High resistivity in the silicon layers was found important for achieving high transmittance and finesse, especially at the longer wavelengths. Also considered are technological factors such as surface roughness, bowing, and misalignment for various proposed manufacturing …

Far-Infrared/Millimeter Wave Source And Component Development For Imaging And Spectroscopy, Todd Du Bosq

Electronic Theses and Dissertations

The far-infrared and millimeter wave (FIR/mmW) (wavelength 75 micrometer to 10 mm) portion of the electromagnetic spectrum is fairly underdeveloped technologically, owing to the large amount of atmospheric attenuation in that range. At present, the FIR/mmW region is lacking in compact, high-brightness radiation sources and practical imaging systems. This dissertation focuses on development of two complementary technologies in this area - an active mmW imaging system and high-reflectivity Bragg mirrors for the FIR p-Ge laser. The imaging system uses a vector network analyzer in the frequency range of 90-140 GHz as the radiation source and receiver. Raster scanning is used …

Study Of Propagation And Detection Methods Of Terahertz Radiation For Spectroscopy And Imaging, Aparajita Bandyopadhyay

Dissertations

The applications of terahertz (THz, 1 THz is 1012 cycles per second or 300 pm in wavelength) radiation are rapidly expanding. In particular, THz imaging is emerging as a powerful technique to spatially map a wide variety of objects with spectral features which are present for many materials in THz region. Objects buried within dielectric structures can also be imaged due to the transparency of most dielectrics in this regime. Unfortunately, the image quality in such applications is inherently influenced by the scattering introduced by the sample inhomogeneities and by the presence of barriers that reduces both the transmitted power …

Development Of A Fourier Transform Far Infrared (Ftfir) Spectrometer To Characterize Broadband Transmission Properties Of Common Materials In The Terahertz Region, William Paul Ford

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With sub-millimeter wave or terahertz devices becoming more readily available, there is interest in developing sensors in this region of the spectra. To support this interest, we have developed a Fourier Transform Far InfraRed (FTFIR) spectrometer to characterize broadband transmission and reflectance coefficients of materials. The spectrometer utilizes a broadband blackbody source, a Michelson interferometer, and silicon bolometer. The path difference in the Michelson is obtained using a linear stage and data acquisition and stage control were both implemented in a Labview programming environment. The details of the experimental setup and experimental results are presented in this thesis. The instrument …

Characteristics Of Nanocomposites And Semiconductor Heterostructure Wafers Using Thz Spectroscopy, Hakan Altan

Dissertations

All optical, THz-Time Domain Spectroscopic (THz-TDS) methods were employed towards determining the electrical characteristics of Single Walled Carbon Nanotubes, Ion Implanted Si nanoclusters and Si_1-xGe_x HFO₂, SiO₂ on p-type Si wafers.

For the nanoscale composite materials, Visible Pump/THz Probe spectroscopy measurements were performed after observing that the samples were not sensitive to the THz radiation alone. The results suggest that the photoexcited nanotubes exhibit localized transport due to Lorentz-type photo-induced localized states from 0.2 to 0.7THz. The THz transmission is modeled through the photoexcited layer with an effective dielectric constant described by a Drude …