Band-edge absorption characteristics of semi-insulating indium phosphide under unified Franz-Keldysh and Einstein models

The foundational Franz-Keldysh effect and Einstein model are applied in this work to characterize semiconductor band-edge absorption—and its departures from ideality. We unify the Franz-Keldysh and Einstein models to fully characterize the field-induced tunneling of photoexcited electrons from degenerate valence bands into the conduction band, with encroachment into the band gap arising as an Urbach tail. Our unified model is implemented for semi-insulating indium phosphide (SI-InP) with strong agreement seen between the theoretical and experimental results for varied photon energies and electric fields

Fixel based analysis of relapsing remitting multiple sclerosis subjects

Magnetic resonance imaging (MRI) is an important tool in the diagnosis and monitoring of multiple sclerosis (MS). Diffusion MRI can be used to probe changes in normal appearing white matter (NAWM) through its ability to image changes in water diffusivity. Standard diffusion imaging techniques such as diffusion tensor imaging (DTI) are limited in their ability to quantify regions containing complex fibre geometries. The technique of fixel-based analysis (FBA) extracts information on the properties of fibre bundles within white matter and has shown advantages in analyzing areas containing complex fibre geometries. In this work, FBA and DTI analysis were applied to a set of relapsing remitting MS subjects (RRMS) and healthy controls. An image analysis pipeline was created to extract fixel-based and DTI metrics for MS lesions, NAWM adjacent lesions, and all NAWM. Comparisons were made between fixel-based and DTI metrics for differing disease modifying therapy (DMT) treatments in the three brain regions. We found significant differences in both fixel-based and DTI metrics between RRMS subjects and healthy controls. We found that the NAWM adjacent to MS lesions showed significant differences in fixel-based and DTI metrics compared to MS lesions and NAWM. Differences in fixel-based and DTI metrics between MS lesions and NAWM may indicate that fixel-based metrics can probe disease that extends out from MS lesions into NAWM. Analysis was performed to compare fixel-based and DTI metrics based on DMT. No significant trends were found between DMTs in terms of fixel-based and DTI metrics. This analysis is limited by the low sample sizes in this work. Further studies are needed to determine if small differences in fixel-based and DTI metrics can be observed between DMTs.Science, Irving K. Barber Faculty of (Okanagan)Computer Science, Mathematics, Physics and Statistics, Department of (Okanagan)Graduat

Urbach-edge-assisted electro-absorption for enhanced free-space optical modulation

In this work, we introduce an electro-absorption (EA)-based retro-modulator for effective realization of free-space optical communications via passive downlinks. Demands for deep modulation and broad directionality in such links are met by its corner-cube assembly of EA-modulators. The EA-modulators use semi-insulating InP as its band edge absorption exhibits an Urbach tail near the 980-nm wavelength of the laser light. This enables Urbach-edge-assisted EA, which allows the field-induced absorption to be optimized via temperature. The theory, from a uniting of the Einstein model and Franz-Keldysh effect, and experiments, from a prototype, show good agreement with deep (greater than 15%) modulation depths. Such functionality can meet the key demands of emerging free-space optical communication links.Applied Science, Faculty ofEngineering, School of (Okanagan)ReviewedFacult

A methodology for dynamic material characterizations via terahertz time-domain spectroscopy.

In this work, the challenges of terahertz (THz) time-domain spectroscopy on complex (multilayer) samples with time-varying (dynamic) characteristics are addressed. The challenges appear in characterizations of the refractive index and extinction coefficient, as etalon artifacts due to internal reflections, and are accentuated in multilayer structures having dynamic and low-loss materials, such as biomolecular materials. This is because nonidealities may form as airgaps at the interfaces and as inhomogeneity in the bulk. The proposed methodology addresses the challenges by introducing a generalized model that accommodates dynamic formation of airgaps and inhomogeneity. It is shown that the generality of the model allows it to mitigate etalon artifacts and yield a highly accurate representation of the material characteristics, with low systematic error, even for low-loss materials. The methodology is applied to characterizations of quartz and glucose in the THz spectrum to see fine detail in the characteristics of quartz and the crystallization of glucose.Applied Science, Faculty ofArts and Social Sciences, Irving K. Barber Faculty of (Okanagan)Engineering, School of (Okanagan)ReviewedFacult

The dynamic morphology of glucose as expressed via Raman and terahertz spectroscopy

The proposed work introduces time-captured Raman and terahertz spectroscopic analyses as orthogonal probes of intramolecular and intermolecular modes in biomolecular structures. The work focuses on glucose given the complexity and dynamics of its anomeric conversion and crystallization. The Raman analyses capture the dynamics of its intramolecular modes – revealing conversion between α and β anomers. At the same time, the terahertz analyses capture the dynamics of its intermolecular modes – showing an evolution from amorphous to crystalline morphology. It is shown that time-captured Raman and terahertz spectroscopy together render a more complete depiction, and deeper understanding, of the biomolecular structure of glucose.Applied Science, Faculty ofScience, Irving K. Barber Faculty of (Okanagan)Chemistry, Department of (Okanagan)Computer Science, Mathematics, Physics and Statistics, Department of (Okanagan)Engineering, School of (Okanagan)ReviewedFacult