Controlled photothermal ablative processing of commercial polymers minimizing undesired thermal effects under high frequency femtosecond laser irradiation

Abstract

The response of three commercial polymers (poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET) and polypropylene (PP)) with different thermal properties under high repetition rates (1 kHz-1 MHz) with femtosecond (450 fs) multi-pulse laser irradiation at λ = 515 nm (1.4 J/cm2) is reported resulting in a complete study with controlling the ablation depth and minimizing collateral thermal effects. Tunable ablation depth is achieved accurately by varying the repetition rate at a constant fluence. The results are compared to a photothermal model that aims at explaining the heat accumulation effect of successive pulses as a function of the repetition rate and predicts three different heat regimes (non-cumulative, cumulative and saturation). The threshold frequencies for each regime can be estimated from the model, providing control for selecting frequency values and thermal regimes. Thermal analyses are performed to characterize the materials, concluding that thermal parameters are vital for selecting optimal materials and laser processing parameters.