Bond-breaking mechanism of vitreous silica densification by IR femtosecond laser pulses

¹ University of Missouri, Department of Mechanical and Aerospace Engineering - E 2412 Lafferre Hall, Columbia, MO 65211, USA
² Institut Lumière Matière, UMR 5306 CNRS - Université Lyon 1, Université de Lyon F-69622 Villeurbanne Cedex, France
³ Joint Institute for High Temperatures, RAS - 13 Bld. 2 Izhorskaya str., Moscow 125412, Russia

Received: 14 March 2016
Accepted: 29 April 2016

Abstract

The densification of the vitreous silica (v-SiO₂) due to laser irradiation appears reasonable to cause the change in refractive index. In this letter, the v-SiO₂ densification under IR femtosecond laser irradiation is studied within molecular-dynamics simulation. The single- and multi-pulse interactions are explored numerically with an account of the bond-breaking mechanism. By analyzing the network at nanoscale, the nature of v-SiO₂ densification is assigned to the reduction of major ring fractions of six- and seven-membered rings to minor fractions of three- and four-membered rings (related to D₂ and D₁ Raman signatures, respectively). The athermal behavior of v-SiO₂ densification is disclosed at different degrees of ionization for both the single- and multi-pulse cases at sub-threshold regimes. The good agreement between calculated and measured D₂ defect line and Si-O-Si angle changes argues in favor of the found mechanism.