Visible-Terahertz Refractive Indices Correlation in Sodium Borosilicate Glasses

Tostanoski, Nicholas J., and S. K. Sundaram. "Visible-Terahertz Refractive Indices Correlation in Sodium Borosilicate Glasses." Journal of Infrared, Millimeter, and Terahertz Waves (2022): 1-20.

for full paper see https://link.springer.com/article/10.1007/s10762-022-00900-3

Abstract

We report visible-terahertz (THz) refractive indices correlation in the sodium borosilicate glass system along two tie lines, NaBSi and BNaSi. The NaBSi series represents the substitution of silicon dioxide for boron oxide, and the BNaSi series, the substitution of silicon dioxide for sodium oxide. Raman spectroscopy was used to provide insight into glass structure with an emphasis placed on properties including physical, e.g., density (ρ), thermal, e.g., glass transition temperature (Tg), and optical, e.g., refractive indices and dispersion at visible and THz frequencies. A prism coupler system equipped with multiple visible wavelength laser sources and terahertz time-domain spectroscopy (THz-TDS) were used to record refractive indices at visible and THz frequencies, respectively. Sodium borosilicate glasses with a depolymerized glass network, R > 0.5, consisting of charge deficient [BØ4]− borate and Q4 silicate tetrahedra forming borosilicate ring units with mixed Si–O–B bridges, and formation and increased quantities of Q3 silicate tetrahedra with more polarizable non-bridging oxygen (nbO) atoms are responsible for higher measurable refractive indices in these frequencies. This work shows that a linear correlation exists between refractive indices across these frequencies. Additionally, depolymerized glass networks record larger density, glass transition temperature, and optical basicity values. In terms of glass structure, refractive indices of depolymerized or polymerized networks measured at 0.589 μm and 0.5 THz support the correlation, which will be useful for developing active and passive components for applications across these frequencies.