In recent years, many applications have been recognized for biomedical imaging techniques utilizing terahertz frequency
radiation. This is largely due to the capability of unique tissue identification resulting from the nature of the interaction
between THz radiation and the molecular structure of the cells. By THz identification methods, tissue changes in tooth
enamel, cartilage, and malignant cancer cells have already been demonstrated. Terahertz Time-Domain Spectroscopy
(THz-TDS) remains one of the most versatile methods for spectroscopic image acquisition for its ability to
simultaneously determine amplitude and phase over a broad spectral range.
In this study we investigate the use of THz imaging techniques to uniquely identify damage types in tissue samples for
both forensic and treatment applications. Using THz-TDS imaging in both transmission and reflection schemes, we
examine tissue samples which have been damaged using a variety of acids. Each method of damage causes structural
deterioration to the tissue by a different mechanism, thus leaving the remaining tissue uniquely changed based on the
damage type. We correlate the change in frequency spectra, phase shift for each damage type to the mechanisms and
severity of injury.
Terahertz based spectroscopy and imaging has become an active field of research in the past decade for a plethora of
applications including security screening, biomedical imaging, chemical analysis, and investigation of carrier dynamics.
Several advantages exist for the use of THz techniques since investigation of a sample can be performed without contact
or ionization; however, fine detail is difficult to determine due to the diffraction limit of the radiation. The resolution
limit of THz imaging and sensing can be overcome by the incorporation of near-field optical techniques; which can
allow image resolution as fine as tens of nanometers at THz frequencies. With this expanded resolution capability, THz
imaging can decipher micro- and nano-structural information which, when coupled with the non-contact features of
these techniques, makes THz spectroscopy ideal for the analysis micro and nano-optical devices. In this study, we
demonstrate the development and performance of an aperture-less near-field system which has been integrated to
perform highly-spatially resolved Terahertz Time-Domain Spectroscopic (THz-TDS) imaging.
Imaging with electromagnetic radiation in the THz frequency regime, between 0.2 THz and 10 THz, has made
considerable progress in recent years due to the unique properties of THz radiation, such as being non-ionizing and
transparent through many materials. This makes THz imaging and sensing promising for a plethora of applications;
most notably for contraband detection and biomedical diagnostics. Though many methods of generation and detection
terahertz radiation exist, in this study we utilize Terahertz Time Domain Spectroscopy (THz TDS) and THz digital
holography using a coherent, tunable CW THz source. These methods enable access to both the amplitude and phase
information of the traveling THz waves. As a result of the direct time-resolved detection method of the THz electric
field, unique spectroscopic information about the objects traversed can be extracted from the measurements in addition
to being able to yield intensity imaging contrast. Utilizing such capabilities for THz based imaging can be useful for
both screening and diagnostic applications. In this work, we present the principles and applications of several
reconstruction algorithms applied to THz imaging and sensing. We demonstrate its ability to achieve multi-dimensional
imaging contrast of both soft tissues and concealed objects.
In recent years a great amount of research has been focused on metamaterials, initially for fabrication of left-handed
materials for use in devices such as superlenses or electromagnetic cloaking. Such devices have been developed and
demonstrated in regimes from the radio frequency all the way to infrared and near optical frequencies. More recently, it
has been shown that, by careful adjustment of the effective permittivity and permeability, near perfect electromagnetic
absorbers can be realized. High absorption occurs when transmission and reflection are simultaneously minimized. With
some clever tuning of the electric and magnetic responses, the electric and magnetic energy can therefore both be
absorbed by the same metamaterial structure.
In this work we present the design, simulation and characterization of a novel thin, flexible, polarization insensitive
metamaterial absorber. Finite-element simulation results show that this device achieves almost perfect absorption at THz
frequencies. Each unit cell of the absorber is made up of two metallic structures separated by a dielectric filler material.
The electric response can be tuned by adjusting the geometry of the top metallic electric ring resonator structure. We
demonstrate that a rotation about the axis of THz wave propagation at normal incidence does not change the absorption
or the resonance frequency by a significant amount. A value of absorption of 99.6 % at a resonance frequency of 0.84
THz can be achieved. We also demonstrate the characteristics of this absorber structure under various THz wave
incidence angles, with respect to both the incident electric and magnetic fields.
Quantum dot (QD) functionalized nanowire arrays are attractive structures for low cost high efficiency solar cells. QDs
have the potential for higher quantum efficiency, increased stability and lifetime compared to traditional dyes, as well as
the potential for multiple electron generation per photon. Nanowire array scaffolds constitute efficient, low resistance
electron transport pathways which minimize the hopping mechanism in the charge transport process of quantum dot
solar cells. However, the use of liquid electrolytes as a hole transport medium within such scaffold device structures
have led to significant degradation of the QDs. In this work, we first present the synthesis uniform single crystalline ZnO
nanowire arrays and their functionalization with InP/ZnS core-shell quantum dots. The structures are characterized using
electron microscopy, optical absorption, photoluminescence and Raman spectroscopy. Complementing
photoluminescence, transmission electron microanalysis is used to reveal the successful QD attachment process and the
atomistic interface between the ZnO and the QD. Energy dispersive spectroscopy reveals the co-localized presence of
indium, phosphorus, and sulphur, suggestive of the core-shell nature of the QDs. The functionalized nanowire arrays are
subsequently embedded in a poly-3(hexylthiophene) hole transport matrix with a high degree of polymer infiltration to
complete the device structure prior to measurement.