"First-principles calculations of fused silica electronic structure under strong laser-induced excitation" by Arshak Tsaturyan

Seminar by Arshak A Tsaturyan, Laboratoire Hubert Curien

Abstract

Fused silica is an indispensable material in emergent photonic applications due
to its unique optical, mechanical, and thermal properties, especially when it is
nano-structured by an ultrashort laser pulse. The precision of the laser-induced
modifications relies heavily on the control of the electron excitations and transient
optical properties during the laser pulse. A first-principles model was applied to
determine dynamic distortions of energy bands following the rapid increase in the
free-carrier population in an amorphous dielectric excited by an ultrashort laser
pulse. Fused silica glass is reproduced using a system of (SiO4)4- tetrahedra,
where Density Functional Theory extended to finite-temperature fractional
occupation reproduces ground and photoexcited states. Using an original
molecular model of photoexcited fused silica, we show that when excited,
electrons relocate spatially from silicon to oxygen, massively decreasing the ionic
bond strength. As a result, infinitesimal displacement of atoms is observed. This
atomic rearrangement is unexpectedly fast and leads to a significant bandgap
narrowing on the femtosecond timescale. At very high excitation levels, electron
redistribution triggers ultrafast generation of defects and a cohesion loss in the
structure).

This seminar will be held in english