[9p-Z18-1~21] 3.7 Laser processing

△ [9p-Z18-5] Reduction of the laser penetration depth of titanium induced by below-ablation-threshold femtosecond laser pulse irradiation

〇(D)Yuki Furukawa^1,2, Shunsuke Inoue^1,2, Masaki Hashida^1,2 (1.ICR, Kyoto Univ., 2.GSS, Kyoto Univ.)

Keywords:metal, ablation, optical properties

We have discovered that the pre-irradiation of a femtosecond laser pulse with the fluence below the ablation threshold of the titanium target reduces the ablation by the subsequent irradiation of another femtosecond laser pulse. This result suggested that the below-ablation-threshold pre-irradiation changed the optical properties of titanium surface. To verify this hypothesis, we developed and performed a new pump-and-probe measurement to estimate the temporal change of the effective laser penetration depth induced by the below-ablation-threshold pre-irradiation. At a delay of several hundreds of picosecond, the effective laser penetration depth was reduced to about half of that without pre-irradiation. The reduction of laser penetration depth cannot be explained by simple heating. The change of the electron state by the pre-irradiation was discussed.