Stagnating surface tension below boiling temperature during laser illumination

Abstract Many laser processes include melting of material. Often, the material is overheated and reaches temperatures close or even above boiling temperature. However, many material properties at such high temperatures are often not known. A very important parameter that defines wetting and melt flow behavior is the surface tension coefficient, which is temperature dependent. However, the high temperature environment poses challenges to the measurement systems. This work suggests a surface tension measurement method based on surface wave analysis induced by an intense laser pulse. The results show lower surface tension values than expected from extrapolations just below boiling temperature. In addition, the surface tension is stagnating and not decreasing as typically expected. Based on a simplified estimation of broken bonds in the surface at different temperatures, the results showed that extensive vaporization can lead to increased surface tension coefficients.