[15p-K201-1~8] Crossroads in Applied Physics: New trends in Glass and Laser Processing Technology

4:40 PM - 5:10 PM JST(7:40 AM - 8:10 AM UTC)

[15p-K201-8] Mechanism of femtosecond laser-induced refractive index change in silica glass

〇Yasuhiko Shimotsuma¹, Tsubone Misora¹, Yoshio Kono², Masahiro Shimizu¹, Kiyotaka Miura¹ (1.Kyoto Univ., 2.Kwansei Gakuin Univ.)

Keywords:

silica glass,densification,ultrashort pulse laser

Silica glass is a fundamental material in modern society, thanks to its exceptional properties, including heat resistance, chemical resistance, and transparency. However, the glass structure is inherently irregular and in a non-equilibrium state, resulting in physical properties that fluctuate with the hypothetical temperature. Consequently, the interplay between glass structure and its physical properties remains a subject of ongoing research. Notably, silica glass, in contrast to ordinary glass, undergoes a decrease in volume and an increase in density with rising virtual temperature. We have utilized the localized ultra-high-cooling-speed induced by focused femtosecond laser irradiation within silica glass to unveil a range of structural modifications, including an increase in the refractive index due to structural densification (Type I) and the emergence of birefringence resulting from the self-assembled periodic nanostructure (Type II). Recent studies have revealed that the coordination number and density of silica glass changes under high pressure. In this study, we evaluated the structural changes in the glass induced by high-pressure treatment and femtosecond laser irradiation by synchrotron X-ray diffraction measurements. Our findings on femtosecond laser irradiation suggest a contribution to the change in the fictive temperature, attributable to localized ultra-high-cooling-state, in addition to the densification mechanism triggered by shock wave generation.