Spatial confinement effects on spectroscopic and morphological studies of nanosecond laser-ablated Zirconium

Spatial confinement effects on plasma parameters and surface morphology of laser ablated Zr (Zirconium) are studied by introducing a metallic blocker. Nd:YAG laser at various fluencies ranging from 8 J cm(-2) to 32 J cm(-2) was employed as an irradiation source. All measurements were performed in the presence of Ar under different pressures. Confinement effects offered by metallic blocker are investigated by placing the blacker at different distances of 6 mm, 8 mm and 10 mm from the target surface. It is revealed from LIBS analysis that both plasma parameters i.e. excitation temperature and electron number density increase with increasing laser fluence due to enhancement in energy deposition. It is also observed that spatial confinement offered by metallic blocker is responsible for the enhancement of both electron temperature and electron number density of Zr plasma. This is true for all laser fluences and pressures of Ar. Maximum values of electron temperature and electron number density without blocker are 12,600 K and 14 x 10(17) cm(-3) respectively whereas, these values are enhanced to 15,000 K and 21 x 10(17) cm(-3) in the presence of blocker. The physical mechanisms responsible for the enhancement of Zr plasma parameters are plasma compression, confinement and pronounced collisional excitations due to reflection of shock waves. Scanning Electron Microscope (SEM) analysis was performed to explore the surface morphology of laser ablated Zr. It reveals the formation of cones, cavities and ripples. These features become more distinct and well defined in the presence of blocker due to plasma confinement. The optimum combination of blocker distance, fluence and Ar pressure can identify the suitable conditions for defining the role of plasma parameters for surface structuring. (C) 2017 Elsevier Ltd. All rights reserved.