Third-harmonic generation monitoring of femtosecond-laser-induced in-volume functional modifications

During the last two decades, ultrafast in-volume laser-based processing of transparent materials has emerged as a key 3D-printing method for manufacturing a variety of complex integrated photonic devices and micro-parts. Yet, identifying suitable laser process parameters for a given substrate remains a tedious, time-consuming task. Using a single laser source for both processing and monitoring, we demonstrate a method based on in situ full-field third-harmonic generation (THG) microscopy that exploits the properties of a low-noise CMOS imager to rapidly identify the entire processing space, discriminating different types of laser-induced modifications, and extracting incubation laws governing the laser exposure process. Furthermore, we show that full-field THG monitoring is capable of identifying parameters leading to enhanced functional properties, such as laser-enhanced etching selectivity. These findings enable accelerated implementations of laser processes of arbitrarily chosen transparent materials and, due to the rapid acquisition time (>100FPS) of the imager, closed-loop process control.