Femtosecond laser-based optomechanical processes for permanent and high-precision fine alignment of optical systems

Miniaturization has been at the forefront of scientific research in the past decade covering diverse areas such as electronics, mechanics, and optics. While 'small is beautiful' may be a vast generalization, the true benefits of miniaturization are especially evident in terms of performance, robustness, packaging density, and manufacturing cost. In this context, femtosecond laser processing of transparent dielectric materials has emerged as a versatile tool for designing complex shapes at the micro-scale. Its three-dimensional (3D) capability, single-step maskless fabrication approach, and material-independent nature bypass many limitations of traditional lithographic methods, thereby enabling the fabrication of micro-mechanical and micro-optical components in glass substrates, as well as their monolithic integration for optomechanical, optofluidic, and other such applications.The subject of this thesis is permanent high-precision alignment of micro-optical components. Here, we explore the use of femtosecond laser processing to fabricate pseudo-monolithic optical assemblies. Specifically, we integrate complex optomechanical functions on a single glass substrate and investigate novel non-contact alignment methods based on complex morphological events that occur within a laser-irradiated region. Due to the non-linear nature of laser absorption, the alignment method distinguishes itself from existing methods by its ability to introduce permanent and controlled sub-nanometer deformations in 3D glass micro-positioners, thereby forming a single monolith on which optical components are placed.First, we discuss some general design principles for micro-positioning elements. Although a plethora of examples can be found in literature, we establish certain constraints, based on which, some designs are chosen for further investigation. Next, we carry out component-level demonstrations by actuating the chosen designs using non-ablative femtosecond laser exposure. The laser exposure strategy, which is a crucial part of the alignment process, is also investigated and optimized. Later on, system-level integration is demonstrated in a fiber-coupling device by combining two alignment functions on a single substrate. Inside a compact design footprint, we achieve a near-theoretical coupling efficiency.Alignment sensitivity requirements vary from case to case and can range between sub-micron down to sub-nm levels. To investigate the resolution capability of femtosecond laser-enabled fine-alignment methods, we test this approach on a Fabry Perot cavity, typically designed for atom trapping applications, and that illustrates an application with extreme resolution requirements.Finally, as an essential parameter for sustainable packaging, we report on the long-term stability of laser-aligned optical systems. There, using a novel micro-tensile testing method, the room-temperature relaxation dynamics of fused silica under static stress conditions are explored for stress levels approaching 2 GPa. This work holds promise for both research and industrial applications. It enhances the potential of femtosecond laser micromachining by adding alignment functions, thereby enabling the fabrication of an 'all-glass optical motherboard'. The potential resolution of this method, combined with the intrinsic material properties of fused silica, are particularly interesting for the packaging of high-precision instruments, such as those for space applications.