Effect of femtosecond-laser process parameters on the surface structure and anti-reflection of surface texture

The high surface reflectivity of metallic materials and their narrow range of electromagnetic wave absorption (primarily in the visible spectrum) severely limit their practical applications in defense, energy conversion, and communication. Therefore, creating surface structures with anti-reflective properties on metallic materials can effectively reduce surface reflectivity and broaden the frequency bandwidth of electromagnetic wave absorption, a goal highly valued by scholars both domestically and internationally. In this study, we investigated the effect of femtosecond-laser process parameters (pulse frequency, processing power, scanning speed, processing time, and focal length) on the dimensional parameters and surface morphology of groove and circular hole structures using a single-factor approach. By varying the femtosecond-laser process parameters, we produced groove and circular hole specimens with different width/diameter-to-depth ratios. The results indicated that with increases in femtosecond-laser pulse frequency, processing power, scanning speed, and processing time, the width and depth of the grooves and circular holes increased to varying extents. We characterized the anti-reflective properties of the textured surfaces to elucidate the mechanism by which the width/diameter-to-depth ratio of the textured structures affects the anti-reflective properties of metal surfaces. The results show that the transverse dimensions and depths of the groove and hole structures increased linearly with increases in femtosecond-laser processing power and the number of processing cycles. The average reflectance of the structures increased from 15.15% to 31.84% when the ratio of structural width (diameter) to depth ranged between 0.43 and 1. The average reflectance of the structures, calculated to be consistent with actual results, ranged from 12.13% to 36.37%. The findings demonstrate that the width/diameter-to-depth ratio of the structure is a crucial index for assessing anti-reflective performance.