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Title: Numerical and experimental investigation of novel materials for laser and amplifier operations
Author: Oladeji, Ayodele
ISNI:       0000 0004 5914 9272
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2015
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One of the most exciting areas of research in optics is rare-earth doped glasses and fibres with capacity for near-infrared to mid-infrared operations. In particular, there is great interest in optimising parameters like ion concentration, fibre length/geometry, and pump conditions for applications in photoluminescence, amplification and lasing. Round trip investigation from material fabrication, experimental setup and actual device can be laborious, expensive and come with some uncertainties. Some of these uncertainties are accurate identification of ion-ion interactions, impact of such interactions on device performance, correct extraction of phenomenological material properties and the prediction of combination of properties with numerical methods. In this thesis, the spectroscopic behaviour of rare-earth doped materials are theoretically studied via numerical simulations and experimentally verified. The models developed are applicable to steady-state and transient behaviour of rare-earths under different excitation conditions. For the simulation, a couple of spectroscopic parameters are needed which have to be obtained in advance from bulk glasses. Parameters like radiative and non-radiative lifetimes are calculated by complementing theoretical analysis with a few experimental measurements. The first part of the research concentrates on the study of ion-ion interactions in different concentrations of erbium doped sol-gel SiO2 prepared by the sol-gel method. The work includes continuous-wave (CW) and pulsed excitation spectroscopic measurement on the glasses that provide data for the model. These measurements together with the rate-equation modelling are used to obtain a physical understanding of the processes responsible for the fluorescence features observed. A particle swarm optimisation technique was used to predict the values of the ion-ion interactions. The behaviour of the 488 nm and 800 nm excitations were consistent with the predictions of the model. Indeed, the agreement between the calculated photoluminescence and the measured emission indicates that the six important processes that influence the ion-ion interactions in the bulk material have been correctly identified and included. With this model of photoluminescence at hand, it was possible to extend it to laser or amplifier configurations. Subsequently, erbium doped ZBLAN glass fibre with lower phonon energy were explored for lasing in the mid-infrared for application to 2.73 µm high-power delivery for tissue surgery. Accurate laser characteristics were predicted for two different designs, including the ultimate thermal designs. Optimum boundary conditions of mirror end-facet reflectivity, fibre length and effects of modelling parameters were addressed. The study is complimented with experimental data of double-clad fibre and the results reported were a clear documentation of the design of erbium doped ZBLAN fiber laser. Finally, the potential of P r3+ doped chalcogenide (GeAs(Ga/In)Se) glass for photoluminescence and lasing at 4.73 µm is studied. This is to answer the research question - Can we extract the spectroscopic parameters and also model the superior property of these novel glasses?. The laboratory facilities and availability of experimental data were decisive in the choice of praseodymium ions as well as inclusion of Gallium or Indium for this part of the research. The superior characteristics of Indium over Gallium for hotoluminescence and consequently device characteristics were studied with the aid of a rate equation model. The phenomenon of photon reabsorption in the chalcogenide fibres were also simulated and verified with experiment. The work has produced a comprehensive numerical model for the simulation of photoluminescence in P r3+doped selenide based chalcogenide glass and fibre from NIR to mid-IR especially in the Gallium and Indium based analogues.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA1501 Applied optics. Phonics