Femtosecond Laser Figuring and Polishing for Freeform Optics Fabrication

Freeform optics revolutionizes imaging systems by enabling compact designs and high-performance capabilities, which are crucial for applications such as augmented and virtual reality, medical diagnostics, biosensing, space exploration, remote sensing, and EUV lithography. However, fabricating freeform optical components presents significant challenges: conventional chemical and mechanical methods generate chemical waste and introduce mid-spatial-frequency errors that degrade imaging contrast. This research seeks to overcome these limitations by establishing ultrafast-laser-based figuring and finishing methods. These methods offer a fast, non-contact, flexible, and precise green solution, paving the way for sustainable, high-quality freeform optics fabrication. We expanded a laser pulse propagation model to simulate the ultrafast-laser-glass interaction processes, including plasma generation, temperature evolution, and material removal. Through interactive modeling and experimental validation, we determined optimum laser processing parameters to precisely control ablation and thermal effects. This approach enables the fabrication of optical-quality surfaces with nanometer precision and sub-nanometer surface finishing, critically without detectable subsurface damage. Key demonstrations include the fabrication of staircase structures and the correction of mid-spatial-frequency-like errors, achieving optical-quality surfaces. Furthermore, we developed a predictive method for generating periodic nanostructures and successfully fabricated microprism structures and arrays. These advancements demonstrate the transformative potential of the proposed figuring and finishing methods, systems, and processes for fabricating complex freeform optics with unprecedented precision, flexibility, and quality.