Experimental study on reflection of high-intensity nanosecond Nd:YAG laser pulses in ablation of metals

• Reflection of nanosecond Nd:YAG laser pulses in ablation of magnesium and tin under ambient air conditions is experimentally studied.
• The experiments show that the reflectivity of metals sharply drops at laser fluence of the plasma formation threshold.
• It was found that surface nano/microdefects present on practical surfaces play a significant role in the plasma formation on the real samples by supplying seeding electrons for an optical breakdown.

The total reflectivity of tin and magnesium in ablation by nanosecond Nd:YAG laser pulses in air is studied. It was found that the high initial reflectivity of the studied metals undergoes a significant drop to values of 0.11 for Sn and 0.16 for Mg within a laser fluence range between about 0.8 and 11 J/cm2. These reduced reflectivity values remain virtually unchanged with further increasing laser fluence. This study shows that a significant reflectivity decrease of the studied metals is caused by plasma formation in front of the irradiated surface. Below the plasma formation threshold, the reflectivity of the studied metals is observed to be virtually independent of laser fluence, indicating a small role of Drude׳s temperature effect on the reflectivity of the studied samples.