Florent Husson

GHz-burst laser polishing is as a promising technique for improving the surface quality of metallic materials, offering key advantages over conventional methods. In this study, two distinct approaches are investigated: a single-step polishing process, and a double-step process consisting of an initial laser milling step followed by a finishing/polishing pass. This distinction is critical in evaluating the performance of GHz-burst regimes under different surface conditions and roughness levels. Initial proof-of-concept trials confirm that GHz-burst irradiation can significantly reduce the surface roughness with minimal thermal damage, provided that process parameters are carefully optimized. Further analysis of spot-to-spot overlap reveals that the deposited energy density plays a crucial role in achieving uniform surface quality without inducing surface defects. The number of passes is also studied, showing that while multiple passes can improve surface finish, the benefit strongly depends on the initial roughness state of the substrate. Scalability is demonstrated by increasing both the repetition rate and scan speed proportionally while maintaining processing quality across larger areas. These results support the viability of GHz-burst laser polishing for high-throughput manufacturing. Applications in aerospace, biomedical implants, and precision optics highlight the technique’s potential for industrial adoption in demanding surface finishing contexts.

Precision micromilling is currently widely used for the fabrication of injection mold inserts for the mass production of microfluidic devices. However, for complex devices with micrometer-scale and high density of structures, micromilling results in high production times and costs for production runs of hundreds or thousands of units. Femtosecond laser (fs-laser) technology has emerged as a promising solution for high-precision micromachining. This study analyzes the potential of fs-laser micromachining for the fabrication of injection mold inserts for the large-scale production of thermoplastic microfluidic devices. For the evaluation of technology, a reference design was defined. The parameters of the fs-laser process were optimized to achieve high resolution of the structures and optimal surface quality, aiming to minimize production times and costs while ensuring the quality of the final part. The microstructures were replicated in two different grades of COC (Cyclic Olefin Copolymer) by injection molding. The dimensional tolerance of the structures and the surface finish achieved both in the insert and the polymer parts were characterized by scanning electron microscopy (SEM) and confocal microscopy. The surface quality of the final parts and its suitability for microfluidic fabrication were also assessed performing chemical bonding tests. The fs-laser machining process has shown great potential for the mass production of microfluidic devices. The developed process has enabled for a reduction of up to 90% in the fabrication times of the insert compared to micromilling. The parts exhibited very smooth surfaces, with roughness values (Sa) of 64.6 nm for the metallic insert and 71.8 nm and 72.9 nm for the COC E-140 and 8007S-04 replicas, respectively. The dimensional tolerance and the surface quality need to be improved to be competitive with the finishes achieved with precision micromilling. Nonetheless, there is still room for improvement considering the significant reduction in the production times through new laser processing strategies.