Crater geometry characterization of Al targets irradiated by single pulse and pulse trains of Nd:YAG laser in ambient air and water

High intensities laser pulses are capable to generate a crater when irradiating metal targets. In such condition, after each irradiation significant ablation occurs on the target surface and as a result a crater is formed. The crater characterization is very important specifically for some applications such as micromachining. In this paper, the crater formation in metal targets was studied experimentally. The planar aluminum 5052 targets were irradiated by frequency doubled (532 nm), Q-switched Nd:YAG (∼6 ns) laser beam in ambient air and distilled water. A crater was produced after each irradiation and it was characterized by an optical microscope. Different laser intensities as well as pulse trains were applied for crater formation. The effects of laser characteristics in crater geometry were examined. The depth of the craters was measured by optical microscope and the diameter (width) was characterized by processing of the crater image. The results were explained in terms of ablation threshold and plasma shielding. The results show that the crater geometry extremely depends on the laser pulse intensity, the number of laser pulses, and ambient.