Dynamics of femtosecond laser ablation of fused silica by oscillation of time-resolved reflectivity

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

We have observed an oscillation with ca. 60 ps-period in time-resolved reflectivity of fused silica excited by a femtosecond laser pulse with fluence of 4.9-12.8 J/cm. We consider that the oscillation is caused by an interference between reflected probe pulses from front and rear surfaces of liquid-vapor (LV) coexistence phase. The phase and decay of the oscillation suggest that the LV phase having carrier concentration enough for plasma reflection is not only expanded by thermodynamic homogeneous nucleation of gas bubbles, but also separated into two dense layers by tensile stress wave.