Wavelength Effects on the Reflectivity of Niobium by Solid-State Laser Pulses

Abstract

This study utilized solid-state lasers with a 50 ns pulse duration in a Q-switched mode of operation at wavelengths of 1.06 µm and 0.69 µm to investigate the hemispherical reflectivity of niobium. Our experimental results show that the reflectivity of niobium decreases notably as the laser fluence increases towards the plasma formation threshold for ablation at both studied wavelengths, which we attribute to changes in the absorptivity of the surface resulting from plasma formation. We also observed a significant effect of laser wavelength on the reflectivity values of the sample at low laser fluence. By determining the threshold fluence values for each wavelength, we estimated the surface temperature associated with the threshold fluence for plasma formation. Our calculations revealed discrepancies between published values for optically polished and mechanically polished niobium, which we suggest may be due to the presence of nano/micro defects, oxide films, and contaminants that amplify the wavelength-dependent effects on reflectivity. These findings have important implications for the design of optical components and laser processing techniques that use niobium, as well as for the development of accurate models of laser-material interactions. Further research is needed to fully understand the underlying mechanisms driving the observed effects and to explore potential applications of niobium in laser-based technologies.