Dynamic monitoring of femtosecond-laser in-volume processing of glass substrates

The non-ablative interaction of femtosecond lasers with transparent substrates gives rise to complex phenomena yielding a rich taxonomy of surface and volumetric material structural changes. Stemming from the inherent cumulative nature of the interaction, i.e. the response to each pulse depends on that of its predecessors, these phenomena remain complex to control, as the outcome results from concurrent and cascading events with diverse time constants. Here, we explore a fast method operating at 10 MHz, based on the monitoring of absorption mechanisms in the mid-infrared domain to dynamically observe laser-induced events, such as bubble nucleation, crack formation and localised melting.