Investigating Ultrafast Laser Modification of Silicate Glass Structure
Date
2021-08
Authors
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Publisher
New York State College of Ceramics at Alfred University. Inamori School of Engineering.
Abstract
High-intensity femtosecond laser pulses have the necessary field strength to induce nonlinear ionization processes in glasses, resulting in permanent modification to structure and optomechanical properties. While ultrafast laser modification of vitreous silica has received much attention, the effect of laser radiation on multicomponent SiO2-based glasses remains unclear. This thesis aims at developing silicate glasses with superior strength through a densification process using ultrafast pulse laser radiation, characterizing the structural changes, and establishing the mechanisms responsible. The impact of laser modification on glass structure remains highly dependent on several variables. Three of those variables studied in this body of work are repetition rate, fluence, and glass chemistry.
The first part of this work focuses on the ability to alter glass surface hardness after exposure to high-intensity femtosecond laser pulses with high-repetition rates. Densification in aluminosilicate and decompaction of soda-lime silica, and concomitant increase and decrease in refractive index, respectively, begs the question of whether this phenomenon is compositionally dependent or contingent on laser parameterization. In search of an answer, two soda-lime silicate systems, with systematically varying Na2O:SiO2 and CaO:SiO2 ratios, were exposed to low-repetition rate laser pulses. The results led to the following conclusions: 1) repetition rate induces vastly different laser - glass interactions, increasing fictive temperature promotes decompaction, and densification via shockwave propagation, 2) laser peak intensities are directly proportional to densification, and 3) modifier valency acts as a rate-limiting factor for distortion to glass structure by laser irradiation.
A comprehensive study integrating molecular dynamic simulations and experimentation of low-repetition rate laser exposure to calcium aluminosilicate glasses (along the tectosilicate join) confirmed densification trends. Both experimental and simulated results exhibit an increase in Al^v concentration within the augmented residual density field, relative to laser fluence. Consequently, laser radiation densifies calcium aluminosilicate glasses through enhanced crosslinking.
Description
Thesis completed in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Glass Science at the Inamori School of Engineering, New York State College of Ceramics at Alfred University
Type
Thesis
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Keywords
Glass--Technological innovations, Glass--Mechanical properties, Glass