Thesis (Ph.D.)--Victoria University (Melbourne, Vic.), 2008.

Thesis (Ph. D.)--University of Idaho, 2006. / "May 31, 2006." Includes bibliographical references (leaves 94-101). Also available online in PDF format.

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Innovations in optics and photonics are crucial to propel forward the technologicaladvancement of our society. In particular, the phenomenon of photon upconversion using lanthanide ions holds great potential for many applications such as solar energy harvesting, bioimaging, and anti-counterfeiting technologies. During my journey of studying lanthanide- doped upconverting nanoparticles, I helped discover the first nanoparticles doped with Thulium (Tm) ions that exhibit the photon avalanching (PA) behavior. PA is a special case of photon upconversion; our discovery, called avalanching nanoparticles (ANPs), was exciting for the field because it exhibits highly optically nonlinear behavior and increases the quantum efficiency of the upconversion process by an order of magnitude compared to regular upconversion, thus opening up new applications. In this thesis, three major applications are explored: viral disinfection, photoswitching, and bioimaging. To study how ANPs can be applied for viral disinfection, we used photoluminescence measurements to observe the UV emission from ANPs when pumped with a 1064nm laser. The emissions at 360nm and 340nm correspond to the 1D2 to 3H6 and 1I6 to 3F4 energy level transitions in Tm respectively. While the 290nm emission, corresponding to the 1I6 to 3H6 transition, was not observed due to limitations within the optical setup, it is safe to infer that they do exist since the 340nm emission comes from the same excited state. All three of the aforementioned emissions are within the UV spectrum and are germicidal. To understand how many ANPs, and how much pump power is needed to disinfect a surface area, we proposed to incorporate ANPs inside N95 masks, and disinfect them with NIR (1064nm) light. We modeled various parameters: laser power (10- 100W), ANP in polymer volume (1.5-15%) and the quantum yield of ANPs (0.3-10%). Most of the calculation yielded a faster disinfection rate than the current state-of-the-art. Disinfecting with NIR light compared to UV is thus not only more efficient, but is also better and safer for the materials and humans present. While doing measurements on ANPs, I unexpectedly observed them blinking on and off mid-measurement. This is surprising because they were supposed to be extremely photostable according to all the literature on upconverting nanoparticles in the last couple of decades. To better understand this, we did various experiments to rule out any external possibilities with photoluminescence microscopy, atomic force microscopy, and temperature measurements; we concluded the blinking was an intrinsic property of the Tm ions. We learned to deterministically control the blinking process, In the end, we demonstrated several potential applications with the photoswitching property of ANPs, including super resolution imaging. To demonstrate bioimaging with ANPs, we incubated ANPs in MDA-MB-231 cancer cells rich with receptors. We showed that just like single ANPs on a coverslip, ANPs in cells can also show sub-100nm resolution when imaged with a laser scanning confocal microscope. To better understand how ANPs are distributed within a given cell, 3D sectioning is performed on a cell with 11 frames in the XY direction, 1 um away from each other in the Z direction. With quantitative analysis of the distribution of ANP emission, we concluded that the ANPs were distributed mostly as monomers, with decreasing chance of forming small clusters of dimers, trimers, and quadruplets. This could infer the clustering tendencies of the cancer cell receptors. Imaging with ANPs as the probe thus offer the capability of conducting quantitative analyses that fluorescent probes don’t.

L’émergence des verres dopés à l’erbium a permis le développement d’une multitude d’applications. Toutefois, plusieurs de ces applications comme le LIDAR, la spectroscopie infrarouge et la génération de radiation infrarouge pour les oscillateurs paramétriques optiques pourraient bénéficier d’un milieu possédant une large plage de gain au-delà de celle offerte par l’erbium. C’est ce que permet le thulium avec sa plage de gain s’étalant de 1.7 μm à 2.1 μm. Entraînés par les succès de l’erbium pour la production d’impulsions, plusieurs chercheurs transposent les concepts développés pour l’erbium vers le thulium. Parmi les différentes méthodes de conception d’une cavité laser, les cavités linéaires à rétroaction distribuée ou à miroirs de Bragg permettent la mise en place d’un laser monolithique de très petite taille. Selon le schéma de pompage, il est possible d’opérer un tel laser en régime continu tout comme en régime impulsionnel. Ce document présente la mise en application d’un laser à fibre dopée thulium muni d’une cavité linéaire avec miroirs de Bragg. Dans un premier temps, nous présentons le modèle utilisé pour effectuer la simulation du comportement dynamique du laser. Ce modèle permet d’implémenter un algorithme de simulation numérique capable de prendre en considération l’excitation impulsionnelle, les effets dispersifs induits par le réseau de Bragg et les effets non linéaires intrinsèques à la fibre optique. Ensuite, on présentera la caractérisation des différentes composantes nécessaires à la réalisation du laser au thulium, notamment l’amplificateur à l’erbium pour la production d’impulsions pompe de haute énergie pour l’excitation impulsionnelle du laser à fibre dopée thulium. Enfin, on présentera les performances du laser muni de miroirs de Bragg qu’on comparera aux résultats de simulations numériques. / The emergence of erbium doped glasses has allowed the development of many technologies. However, applications such as LIDAR, infrared spectroscopy and infrared sources for optical parametric oscillators all benefit from having a wide gain bandwidth farther in the infrared than what erbium doped glasses allow. Thulium has shown to be a good candidate for such applications due to its wide gain bandwidth ranging from 1.7 μm to 2.1 μm. Inspired by the success in laser pulse generation from erbium doped media, many researchers decided to apply the knowledge acquired from erbium doped laser sources to thulium doped laser sources. We chose to use a linear distributed Bragg reflector cavity, which allows us to implement a monolithic laser of a very small size. Depending on the pumping scheme, it is possible to operate this laser in a CW regime as well as in a pulsed regime. This document details the implementation of a thulium doped fiber laser in a linear cavity with distributed Bragg reflectors. We first develop the theoretical model used for the simulation of our laser’s dynamics. This model allows us to implement numerical simulations able to treat pulsed pumping, dispersive effects induced by the fiber Bragg grating and intrinsic nonlinear effects. We then characterize the erbium-ytterbium doped phosphate fiber amplifier used to generate pump pulses, along with the other components of the thulium doped fiber laser cavity. The numerical model is then validated by comparing numerical simulations to experimental results obtained from our thulium doped laser.

Thesis (MSc)--University of Stellenbosch, 2011. / Please refer to full text to view abstract.