Femtosecond Laser Pulse-Induced Structural Modification of Lanthanum Aluminosilicate Glasses: Refractive Indices in Visible Vs. Terahertz Frequency Regions
Dobesh, David Kotaro, S. K. Sundaram, and R. E. Youngman. “Femtosecond Laser Pulse-Induced Structural Modification of Lanthanum Aluminosilicate Glasses: Refractive Indices in Visible Vs. Terahertz Frequency Regions.” Journal of Infrared, Millimeter, and Terahertz Waves 41, no. 2 (2020): 171-193.
We studied femtosecond laser modifications of lanthanum aluminosilicate (SAL) glasses with 11–23 mol% La2O3 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. 27Al 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.
…Sample thickness was determined using a calibrated OriginCal caliper. A TeraView TPS 3000 was used for THz-TDS measurements. THz spectra were collected from 0 to 3 THz under ambient conditions in transmission mode detection. Initial reference spectra were collected before sample data collection in pure nitrogen. Incident THz radiation energy was produced from a mode-locked Ti:Sapphire laser with a 800 nm central wavelength, pulse duration of 100 fs, and a repetition rate of 80 MHz. The incident THz pulse was divided into both pump and probe beams…