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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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.

No description available.

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

In this dissertation, an all-fiber-based single frequency nanosecond pulsed laser system at ~ 1918.4 nm in master-oscillator-power-amplifier (MOPA) configuration is present. The nanosecond pulse seed is achieved by directly modulating a continuous wave (CW) single frequency fiber laser using a fast electro-optical modulator (EOM) driven by an arbitrary waveform generator (AWG). One piece of single mode, large core, polarization-maintaining (PM) highly thulium-doped (Tm-doped) germanate glass fiber (LC-TGF) is used to boost the pulse power and pulse energy of these modulated pulses in the final power amplifier. This laser system can work in both high power and high energy regime: in high power regime, to the best of our knowledge, the highest average power 16 W and peak power 78.1 kW are achieved for single frequency transform-limited ~2.0 ns pulses at 500 kHz and 100 kHz repetition rate, respectively: In high energy regime, nearly 1 mJ and half mJ pulse energy is obtained for ~15 ns pulses at 1 kHz repetition rate and 5 kHz repetition rate, respectively. Theoretical modeling of the large-core highly Tm-doped germanate glass double-cladding fiber amplifier (LC-TG-DC-FA) is also present for 2&mum nanosecond pulse amplification. A good agreement between the theoretical and experimental results is achieved. The model can simulate the evolution of pump power, signal energy, pulse shape and the amplified stimulated emission (ASE) in the amplifier. It can also be utilized to investigate the dependence of the stored energy in the LC-TGF on the pump power, seed energy and repetition rate, which can be used to design and optimize the LC-TG-DC-FA to achieve higher pulse energy and average power. Two channel of high energy nanosecond pulses (at 1918.4 nm and 1938 nm) are utilized to generate THz wave in a quasi-phase-matched (QPM) gallium arsenide (GaAs) based on difference frequency generation. THz wave with ~ 5.4μW average power and ~18 mW peak power has been achieved. Besides, one model is built to simulate a singly resonated THz parametric oscillator. The threshold, the dependence of output THz energy on pump energy has been investigated through this model. One pump enhanced THz parametric oscillator has been proposed. The enhancement factor of the nanosecond pulses in a bow-tie ring cavity has been calculated for different pulse duration, cavity length and the transmission of the coupler. And the laser resonances in the ring cavity have been observed by using a piezo to periodically adjust the cavity length. We also build an all-fiber thulium-doped wavelength tunable mode-locked laser operating near 2&mum. Reliable self-starting mode locking over a large tuning range (>50 nm) using fiber taper based carbon nanotube (FTCNT) saturable absorber (SA) is observed. Spectral tuning is achieved by stretching another fiber taper. To the best of our knowledge, this is the first demonstration of an all-fiber wavelength tunable mode-locked laser near 2&mum.