Cooling Mechanisms in MHz Femtosecond Laser Processing of Polymers

High repetition rate femtosecond laser processing offers significant benefits for ablation, as higher ablation efficiencies with reduced thermal effects can be achieved by selecting an optimal repetition rate range. In the heat accumulation regime, where the time between pulses is short enough to not allow the material to cool down significantly before the next pulse arrives, ablation cooling occurs. This effect redistributes the thermal energy into material removal, reducing the energy available for heat diffusion and minimizing the extended thermal effects [1]. However, ablation cooling is typically associated to the GHz regime, where plasma shielding dominates and diminishes the ablation efficiency [2], [3]. Nevertheless, polymers, with their low thermal diffusivity and phase transition temperatures, allow the observation of the ablation cooling effects in the MHz regime, avoiding the shielding effects.