Stress-state manipulation in fused silica via femtosecond laser irradiation

Controlling the stress in glass after laser exposure is of prime importance not only for photonics applications, but also for preserving the mechanical integrity of glass components in general. The sub-surface exposure of fused silica to femtosecond laser pulses can induce a permanent and localized modification to the glass structure. In this work, we present evidence that femtosecond laser exposure can be used to continuously tailor the stress in the material, from a tensile to compressive state, as the laser pulse energy is changed. In addition, we demonstrate that this effect can not only be obtained while transitioning between different laser-induced microstructures, but also at low pulse energy, in the laser exposure regime particularly relevant for fabricating waveguides. These results demonstrate that femtosecond laser exposure is a versatile tool for fully controlling the stress landscape in a volume of silica, opening up new technological opportunities, like for instance, direct write stress-free waveguides, direct-write stress-induced birefringence state or mechanically reinforced parts, by locally preloading it.