Effect of Ambient Pressure and Pulse Shaping on Femtosecond Laser Drilling of GDP Films

The quality and precision of polymer film processing via femtosecond laser are frequently degraded by the redeposition of ablated material. Here, we systematically investigate the effects of backing pressure and temporal pulse shaping on the drilling of glow discharge polymer (GDP) films. Reducing the pressure effectively suppresses debris redeposition, improves surface cleanliness, and enhances drilling efficiency. The entrance diameter exhibits a non-monotonic pressure dependence, with a minimum near 10³ Pa, whereas the exit diameter decreases monotonically as pressure increases. At high pressures, through-hole formation becomes increasingly difficult, particularly for pulse sequences with a larger number of subpulses. Low pressure substantially reduces the pulse count required for breakthrough. The observed behavior is interpreted in terms of pressure-dependent nonlinear propagation, focal-position shifts, and plasma shielding. By combining low-pressure operation with an optimized pulse sequence, we obtain high-quality microholes with reduced taper and improved drilling efficiency. These results provide practical guidance for precision femtosecond laser micromachining of polymer films.