Formation of laser induced concentric surface structures on brass and the impact of ambient conditions on it

In this work morphological evolution of brass surface ablated by nanosecond laser is investigated in various ambient environments. Micro level spaced permanent ring structures are perceived for different ambient gas pressures at a fixed number of laser shots and fluences. In case of low background pressure, the generation of concentric ring patterns is observed, and the ring spacing shows a decreasing tendency from the center to the edge. With increase in ambient pressure, the fringe pattern of the rings are found to decrease. Again, in air medium at atmospheric pressure, the concentric ring formation within the laser spot is found to have evidence of molten signature and show increased ring spacing along the radial direction. Initiation of crater formation is observed in air at the center of the laser spot. The cause and possibility to control the morphological transitions among different types of ring structures is discussed.