Femtosecond Laser Pulse-Induced Structural Modification of Lanthanum Aluminosilicate Glasses: Refractive Indices in Visible Vs. Terahertz Frequency Regions

We studied femtosecond laser modifications of lanthanum aluminosilicate (SAL) glasses with 11–23 mol% La 2 O 3 content. Refractive indices of these glasses were measured in the visible and terahertz frequencies and correlated to the change in the glass structure. The role of lanthanum provided a comparison to traditional glass modifiers within the glass network in terms of polarizability and optical basicity for femtosecond laser irradiation modification of the refractive index. 27 Al magic angle spinning nuclear magnetic resonance (MAS-NMR) was used to identify aluminum speciation within the SAL glasses. We used prism-coupling and terahertz time-domain spectroscopy (THz-TDS) for visible and THz refractive index measurements, respectively. Our results show a linear correlation between refractive index measurements in visible and terahertz frequencies with systematic rare-earth ion inclusions. In addition, our results demonstrate that THz-TDS can be utilized as a means of extending the detectable limits in refractive index measurements of disordered glass structures.