Femtosecond laser induced porosity in poly-methyl methacrylate

We show that femtosecond laser ablation of poly-methyl methacrylate (PMMA) induces porosity within the ablation crater that increases with pulse energy/fluence and number of laser shots. For deeper craters the porosity evolves into 3D honeycomb like structure on the sidewalls. Using imaging technique, we show that the porous area fraction decreases with pulse energy while the pore size distribution peaks at a pore area of 0.037 μm2 at higher energies. In line ablation, the pore size increases with the speed at which the laser focus is moved.