Evidence for increased incubation parameter in multi-pulse ablation of a Pt:SS alloy using a femtosecond laser at high repetition rates

The role of reflectivity in multiple pulse incubation of smooth platinum stainless steel (Pt:SS) surfaces was investigated in this study by applying femtosecond pulses with a 500 fs pulse duration at a repetition rate of 100 kHz. Ablated craters were formed by exposure of a femtosecond laser pulse at fluences greater than the damage threshold fluence of the material. Experiments were performed at two different wavelengths, 1030 nm and 515 nm. The craters were characterized using an optical microscope, scanning electron microscopy (SEM) and atomic force microscopy (AFM). An incubation parameter was calculated for Pt:SS at 1030 nm and 515 nm of 0.79 +/- 0.03 and 0.75 +/- 0.02, respectively. The incubation effect was further investigated using reflectivity experiments. Reflectivity experiments were performed using fluences below the damage threshold fluence after each pulse for multiple pulse trains. The reflectivity of unexposed Pt:SS was measured to be 0.71 +/- 0.01 at a wavelength of 1030 nm, and 0.54 +/- 0.04 at a wavelength of 515 nm. The reflectivity changed with increasing number of applied laser pulses. The incubation effect was found to change when applied fluence values were corrected for reflectivity. In the case of accumulated pulses, the incubation parameter was found to be 2.01 +/- 0.04 for 1030 nm and 1.98 +/- 0.02 for 515 nm. Contrary to previous studies on incubation, this study indicates that the incubation effect is significantly reduced with successive pulses, when reflectance is taken into account. The study highlights the important role of reflectivity in incubation and provides new insights into the laser material interaction of alloy materials. (C) 2014 Elsevier B. V. All rights reserved.