Effect of Pulse Duration on Ablation Characteristics of Tetrafluoroethylene-hexafluoropropylene Copolymer Film Using Ti:sapphire Laser

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Abstract
Pulse duration dependence of ablation characteristics of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) film has been investigated with femtosecond and picosecond Ti:sapphire laser pulses at 798 nm. Laser fluence dependence of ablation rates was examined for the laser pulse duration from 170 fs to 12 ps. Surface morphology of ablated holes was investigated using a scanning electron microscope. A great difference has been found in the ablation characteristics for laser pulse durations around 170-fs and longer than 500 fs. From the analysis of the fluence dependence of ablation rates and observation of the ablated surface, we have found that five-photon absorption predominated over other processes only for 170-fs pulses. It has also been found that the ablation threshold intensity was inversely proportional to the square root of the pulse duration in the region from 170 fs to 200 ps.