The Shape of The Exfoliated Surface during Femtosecond Laser Ablation

Femtosecond laser ablation processes on metals are systematically observed using a Ti:sapphire laser pump and the soft x-ray laser probe reflective imaging system. In addition to the dark disk at the femtosecond laser-irradiated spot, an elliptical shadow that expands in the horizontal direction in the nanosecond time domain was observed. We show that the shadow is caused by the exfoliated surface during femtosecond laser ablation. By analyzing the shadow, we can determine the evolution of the exfoliated surface over time. The shape of the film is the result of the relationship between the spatial distribution of the laser beam profile and the ablation threshold of the metal.