Ablation morphology and ablation threshold of Ti-6Al-4V alloy during femtosecond laser processing

The research explores the use of femtosecond laser to clean the surface of Ti-6Al-4V alloy. The laser ablation threshold was determined from either depths or diameters of laser-induced craters. Both methods are expected to give the same results; however, it was found that ablation threshold can be determined more reliably from the diameters than from the depths. This can be understood from the study of the surface morphology. As the laser fluence increased, the ablated surface became increasingly rougher, making it difficult to measure the depths accurately. In contrast, diameters of laser-induced craters could be measured with much better certainty and thus enabled the ablation threshold to be determined more accurately. The ablation threshold was found to be 0.142 ± 0.010 J/cm2 for 100 laser pulses at 130 fs pulse duration and 790 nm wavelength and it tends to decrease with increase in number of laser pulses. The single-pulse ablation threshold was determined to be 0.272 ± 0.021 J/cm2.