Ultrashort Pulsed Laser Micro-Structuring of High-Performance Polymers: From Ablation Fundamentals to Medical Device Fabrication

Ultrashort pulsed (USP) lasers enable material removal with sub-micron precision and minimal thermal damage, making them powerful tools for micromachining. While their use on metals and semiconductors is well established, the response of high-performance polymers remains less understood, despite their growing role in microfluidics, electronics, and biomedical devices. At the same time, microfluidic prototyping faces limitations due to slow and costly mould fabrication. This thesis addresses these gaps by advancing both the understanding of femtosecond laser–polymer interactions and their translation into rapid, low-cost manufacturing methods for microfluidic devices. The overarching aim is to establish a knowledge-based, predictive, and application-ready framework for femtosecond laser structuring of polymers. The research pursues six objectives: (1) characterising ablation thresholds and incubation behaviour; (2) quantifying cumulative effects in scanned ablation; (3) developing a multiphysics ablation model for prediction of material removal; (4) optimising high-repetition-rate ablation for rapid processing; (5) demonstrating polyimide film mould inserts for injection moulding; and (6) in-vestigating and replicating laser-induced periodic surface structures (LIPSS) for wettability control. The results reveal new insights into polymer ablation. Polyimide (PI) exhibits superior stability under femtosecond irradiation, with processing windows identified for precise, damage-free structuring. Scanning experiments showed that ablation rates vary with pulse overlap, and correction factors were introduced to maintain dimensional accuracy even at MHz repetition rates, reducing processing times by up to 90%. A finite element multiphysics model was developed and validated, predicting ablation depths with <5% error and capturing polymer-specific behaviour through an effective enthalpy of ablation. On the applied side, a novel fabrication method was established by bonding laser-structured PI films to steel plates to serve as injection moulding inserts. This enabled the rapid production of microfluidic devices with feature sizes as small as 20 µm. Moulded parts in PMMA and COC showed near 1:1 replication fidelity and mould durability over 100 cycles, demonstrating a practical, low-cost alternative to conventional tooling. In parallel, a design of experiments approach identified conditions for reproducible LIPSS formation on PI. These nanostructures were successfully replicated into thermoplastic polymers, enabling tunable hydrophilic and hydrophobic behaviour. The thesis makes several original contributions: (1) the first quantification of overlap-dependent ablation rate deviations across scanning regimes; (2) a validated finite element model of femtosecond polymer ablation; (3) a rapid prototyping approach using PI film-based mould inserts; and (4) reproducible fabrication and replication of LIPSS for wettability control. Collectively, these results bridge the fundamental science of laser ablation with the applied field of polymer micromanufacturing. The work demonstrates how USP laser processing can be transformed from empirical trial-and-error into a predictive and versatile toolset. By combining modelling, rapid fabrication, and functionalisation, it establishes a foundation for scalable, cost-effective prototyping of microfluidic devices. It highlights broader opportunities in polymer-based electronics, optics, and biomedical engineering.