High-resolution spectroscopy of rare-earth doped novel glasses
Spectroscopic investigations using high-resolution techniques of two novel rare-earth doped glasses are presented. By using high-resolution techniques, the effect of inhomogeneous broadening due to the incorporation of the ion into the glass host is reduced. The aim of this thesis is two-fold. Firstly, to show how the increased resolution these techniques provide can be used to study the ion-host interaction. Secondly, to use this knowledge to explain and predict the performance of the systems under study as components for the optical communications industry. Optical devices have already been demonstrated in the thulium doped fluoride glass ZBLAN. We present site-selective studies that show that the rare-earth ion can occupy two different site subsets within the glass. These subsets are shown to have radiative lifetimes that differ by greater than 10% at 4.2K. This difference, combined with the observation at room temperature of pump wavelength dependent fluorescence, is suggested as an explanation for the disagreement of modelled optical amplifier performance with measured results. Time resolved site selective studies of a highly doped sample allow for the investigation of the thulium-thulium energy transfer process. This allows it to be shown that the transfer process in the absence of resonant energy diffusion is phonon-assisted dipole-dipole transfer. In the search for an optical amplifier to work at 1.3µm, the rare-earth ion praseodymium is a popular candidate. However, to reduce the problems associated with non-radiative decay, glass hosts with low maximum vibrational energies are required. Two such hosts are ZBLAN and the chalcogenide glass Gallium-Lanthanum-Sulphide (GLS). Site-selective studies show that both glasses have spectroscopic features that may affect devices. In ZBLAN, two ion site subsets are again observed. In GLS, there is seen to be a large degree of correlation between the inhomogeneous broadening mechanisms affecting different energy levels. Combined with the room temperature site-selection observed, this will lead to an inhomogeneous amplifier system. In both praseodymium systems, it was demonstrated that persistent spectral holes could be burnt, allowing the homogeneous linewidth of the observed transition to be measured. By monitoring the wavelength dependence of the burning efficiency, it is seen that the interaction of the rare-earth ion with the host in ZBLAN differs greatly in the two site subsets.