High-Temperature Laser Absorption of Steel

Laser light absorption is a complex process including several absorption effects to transfer photonic energy into material. Absorption values and knowledge about impacting factors are relevant to simulate laser processes and get a better understanding of laser-material interaction. However, due to the high temperatures and dynamic melt surfaces of liquid steel, absorption measurements are difficult to conduct. Typically, calorimetric methods for direct absorption measurement or indirect radiometric methods by radiative properties (reflectance, emittance) are used to determine absorption values [1]. Some of the more commonly used methods are laser calorimetry, gonioreflectometry, integrating sphere or integrating mirror reflectometry and emittance spectroscopy [2]. Experimentally, also the determination of absorption in liquid state under different laser processing conditions was possible [3]. E.g. Dausinger &Shen [4] could show that the absorption of $1\ \mu \mathrm{m}$ laser radiation decreases with increasing temperature. Theoretical predictions show differing tendencies for high-temperature absorption values.