In situ photography of picosecond laser ablation of nickel

This work experimentally investigated the time evolution of nickel ablation induced by high-energy picosecond laser pulses. A Nd:YAG laser with a 25 ps pulsewidth was used to perform a pump–probe microphotography experiment. The fundamental and second harmonic wavelengths were used for the pump and probe beams, respectively. The probe beam was delayed in time with respect to the pump beam and was reflected from the ablated surface into a camera to obtain time-resolved images. Photographs of the sample were obtained at the beginning of pump laser irradiation and continued until a time delay of 800 ps. Photographs revealed attenuation of the probe beam beginning during the pump pulse duration and lasting as long as the maximum time delay. Possible explanations of the probe beam attenuation are discussed, including homogeneous nucleation and the metal–dielectric transition near the thermodynamic critical temperature.