Research on the synergistic regulation technology for fabricating stable cross-section and low-taper molybdenum grids based on femtosecond-laser processing

Although femtosecond-laser micromachining of bulk metals has been extensively studied, the coupled effects of energy input, pulse accumulation, and focal position on the material-removal behavior and cross-sectional evolution of ultrathin molybdenum remain insufficiently understood. In this study, the effects of laser energy density, equivalent pulse number, and defocus on cutting-front stability, sidewall morphology, redeposition, and taper formation were systematically investigated. The laser energy density was found to define the stable ablation window and govern the development of periodic sidewall features. The equivalent pulse number controlled the progressive advance of the cutting front and was, therefore, critical to maintaining cross-sectional uniformity. Small variations in defocus near the focal plane produced only limited improvements in taper, whereas large positive defocus substantially reduced the difference in material removal between the entrance and exit surfaces, thereby enabling low-taper cutting. These results establish a direct relationship between processing conditions, sidewall evolution, and cross-sectional geometry in ultrathin Mo sheets. Under the optimized conditions, pure-Mo grids were fabricated with a maximum relative dimensional error of 3.8%, an average relative error below 2%, and a half-taper angle of 14.3°. The findings provide a mechanistic and practical basis for the precision fabrication of Mo-based electron-gun grids and other thin-metal functional microstructures.