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Webinar Series: Materials Studio 5.5

Simulation of Laser Induced Modification of Vitreous Silica

Jim Dickinson from Corning explains femtosecond laser pulse induced structural changes in silica glass and their role in changing the refractive index of the glass have been investigated using ab initio molecular dynamics simulation. Jim reviewed how femtosecond laser pulse induces structural changes in silica glass and how the roles in changing the refractive index of the glass have been investigated using ab initio molecular dynamics simulation. Femtosecond laser irradiation was simulated by raising the electron temperature to 25000 K and allowing the system (72 atom cell) to evolve freely for 300 fs. During the irradiation the average nearest-neighbor Si-O, Si-Si and O-O distances increase due to the weakening of bonds resulting from the thermalization of electrons. Diffusion of Si and O gives rise to a structure with 2- and 3-coordinated Si atoms in addition to non-bridging oxygens. These structural changes are almost completely recovered during post-irradiation evolution of the glass structure. However, there are persistent changes that involve the formation of three-coordinated Si atoms and non-bridging oxygens that correspond to the paramagnetic defect species of Si E' centers and non-bridging oxygen hole centers, respectively. These defects introduce energy levels within the band gap of silica glass giving rise to optical absorptions that increase the refractive index through a Kramers-Kronig mechanism.

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