Effect of flame assistance on hole formation in high-power femtosecond laser drilling of silicon and copper

This work examines the influence of a flame environment on high-power femtosecond laser drilling of silicon and copper. Drilling experiments are conducted at pulse energies ranging from 1.5 to 3.0 mJ, with a focused laser spot size of approximately 50 µm, and the resulting hole geometry, surface morphology, and drilling efficiency are systematically analyzed. Compared with flame-free conditions, the presence of a flame leads to improved edge quality and a pronounced suppression of peripheral spatter for both materials. Quantitatively, the entrance-to-exit diameter ratio is reduced by approximately 50%, while the hole taper decreases by about 30%. In addition, the pulse number required to achieve through-hole formation is reduced by more than half, yielding a two-fold enhancement in drilling throughput and ablation efficiency. These effects are associated with flame-induced modification of the local processing environment, including elevated ambient temperature, altered thermal gradients, and more effective removal of molten material and debris, which collectively promote more uniform material removal along the drilling depth. The results indicate that a flame environment provides an effective means of tailoring femtosecond laser drilling dynamics in silicon and copper, enabling improved geometrical control and enhanced processing efficiency under high-power conditions.