Structural and spectroscopic properties of rare earth doped crystal-in-glass waveguides as influenced by the initial glass composition

Laser induced crystallization of glasses is a highly spatially selective process which has the potential to produced compact, integrated optics within a glass matrix. Specifically, our interest is in using this technique to create a laser. In order to achieve this goal, preliminary research was performed on single crystal lines ``written'' in Er$_{0.002}$La$_{0.998}$BGeO$_{5}$ glass using a femtosecond pulsed laser. This study revealed promising results including incorporation of the erbium into the crystal and the ability to waveguide with low losses, but also illuminated surprising features concerning the distribution of rare earth (RE) ions within the crystal. To further investigate this phenomenon and its potential consequences for our intended application, additional crystalline waveguides were written inside of a series of glasses with compositions of the form RE$_{x}$La$_{1-x}$BGeO$_{5}$, where RE=Pr, Nd, and Er and x=0.002, 0.010, 0.040, 0.100. and 0.200. These structures were analyzed using micro-Raman and luminescence spectroscopy as well as energy-dispersive x-ray spectroscopy.