Investigation of femtosecond laser-enabled 3D micro-infiltration processes

In the last decades, the femtosecond laser micromachining of glass has attracted a lot of attention due to its three-dimensional manufacturing ability and flexibility both in terms of compatible substrates and modification types. Yet, to fully unravel its potential for the production of multi-functional micro-devices, new techniques able to integrate multiple materials in the same glass substrate have to be conceived.In this thesis work, we present a few techniques based on micro-infiltration to integrate both noble metals and glass architectures in a single glass substrate. Specifically, we select femtosecond laser-assisted chemical etching as a means to realize the glass molds and we design a vacuum pressure-assisted micro-infiltration process to cast different materials in fused silica.The first part of the study focuses on femtosecond laser-assisted chemical etching as a manufacturing process. From a technological perspective, (i) we demonstrate the presence of a low laser fluence regime that enables an order of magnitude increase in laser writing speed while maintaining or surpassing selectivity and etching rate obtained for commonly used laser parameters, and (ii) we introduce sodium hydroxide as a novel and more environmentally friendly etching solution and show its superior performance compared to potassium hydroxide and hydrofluoric acid solutions. From the fundamental point of view, we prove that the low laser fluence etching regime is mainly governed by the presence of laser-induced molecular defects, and not by the presence of 'nanogratings', which were usually accounted for the origin of laser-assisted etching selectivity. Further, the observation of an anisotropy in the etching rate for different laser polarization states even with such a low laser fluence suggests that self-organization phenomena are initiated after far fewer pulses than the amount needed for the formation of nanogratings.The second part of the study introduces a pressure-assisted micro-infiltration process and explains the challenges in translating casting to the micron-scale. In particular, we demonstrate the ability of such a process to produce micron-scale architectures of arbitrary geometrical complexity in 3D out of noble metals (silver, gold, copper, and their alloys) and an infrared glass from the chalcogenide family. Additionally, we study its potential for large-scale production compared to existing technologies and explore techniques to produce self-standing glass-metal composites and to perform multiple infiltrations of different materials on the same substrate.This thesis is a step forward in the direction of manufacturing multi-materials monolithic multi-functional glass devices. This combination of materials with completely different properties allows almost unlimited possibilities in terms of designing novel architectures for applications in microtechnologies.