Ablation cooling and thermal regimes in high repetition rate ultrafast laser processing of commercial polymers

Ultrafast laser processing of polymers is strongly influenced by the repetition rate of the irradiation, which determines the balance between heat accumulation and material removal mechanisms. In this work, we investigate the response of a commercial polymer, poly(ethylene terephthalate) (PET), under femtosecond laser irradiation at two different repetition rates: 1 kHz and 60 kHz. Experiments were performed at a wavelength of 1030 nm with 220 fs pulses and a pulse energy of 88 μJ using a beam radius of approximately 118 μm.

The results reveal clear differences in the morphology of the induced structures between the two irradiation regimes. At 1 kHz, extended thermal halos surrounding the ablation crater are observed, associated with local temperature rise above the glass transition threshold. When the repetition rate is increased to 60 kHz, the ablation volumes become significantly larger while the surrounding thermal halos are reduced.

These results indicate that higher repetition rates promote more effective material removal while limiting the extent of the thermally affected regions. This behavior suggests that efficient ablation can act as a heat dissipation mechanism, consistent with the hypothesis of ablation cooling in ultrafast laser processing.