Non-thermal effects on femtosecond laser ablation of polymers extracted from the oscillation of time-resolved reflectivity

時間分解反射率の振動から探る高分子のフェムト秒レーザーアブレーションにおける非熱効果の研究

熊田 高之   ; 赤木 浩; 板倉 隆二; 乙部 智仁; 錦野 将元; 横山 淳

Kumada, Takayuki; Akagi, Hiroshi; Itakura, Ryuji; Otobe, Tomohito; Nishikino, Masaharu; Yokoyama, Atsushi

時間分解反射率測定法を用いて透明高分子のフェムト秒レーザーアブレーションダイナミクスを追ったところ、アブレーション閾値以上の強度のポンプ光入射後に反射率の振動を観測した。本振動は試料表面と、非熱効果によって試料から剥離した薄膜において反射したプローブ光の干渉によるものであると結論付けた。

The dynamics of femtosecond laser ablation of transparent polymers were examined using time-resolved reflectivity. When these polymers were irradiated by a pump pulse with fluence above the ablation threshold of 0.8-2.0 J/cm, we observed the oscillation of the reflectivity caused by the interference between the reflected probe pulses from the sample surface and the thin layer due to the non-thermal photomechanical effects of spallation. As the fluence of the pump pulse increased, the separation velocity of the thin layer increased from 6 km/s to an asymptotic value of 11 km/s. It is suggested that the velocities are determined by shock-wave velocities of the photo-excited layer.