While fused silica microlens arrays (MLAs) act as crucial components in the fields of infrared optics and laser systems, direct laser writing has been proposed for the fabrication of MLAs. However, the layer-by-layer slicing strategy generally leads to stepped surface textures formed on the microlens surface, resulting in high surface roughness and limited transmittance. This work proposes a temperature-controlled CO2 laser polishing method for the fabrication and subsequent smoothing of fused silica microlens arrays. Specifically, an infrared temperature measurement system is integrated into a CO2 laser direct writing platform. Correspondingly, a proportional-integral-derivative algorithm is used to adjust the laser power in real time based on the temperature deviation at the processing spot, thus maintaining the polishing zone in a molten rather than vaporizing state. Furthermore, a finite element model of laser polishing of fused silica coupled with laser heating and fluid flow is developed, which is used to analyze the spatiotemporal evolution of the temperature field, as well as its correlation with the response of the processed surface. Experimental results show that temperature-controlled laser polishing reduces the surface roughness of the fabricated MLAs by 86.8%, while the transmittance in the visible band remains above 90%. This work provides a feasible closed-loop polishing method and a mechanistic analysis model for the laser polishing of fused silica MLAs.
Li et al. (Tue,) studied this question.