Measuring Optical Properties On Rough And Liquid Metal Surfaces

Abstract

For understanding and optimizing laser processing of metals and alloys the optical properties, especially the absorption of the work piece in function of the temperature up to the liquid phase have to be known [1]. There are several approaches to extend the Drude-Model [2] for optical properties of metal to temperature dependence [3, 4, 5]. However, a verification of these models is difficult due to the lack of sufficient experimental data. Even though measuring optical properties with ellipsometry is well established, such measurements on metals and alloys at elevated temperatures up to the liquid state are very challenging. To collect the optical properties of different metals and alloys like Al, Ti, Ag, Cu and steel in the solid and liquid state a custom-made high-temperature ellipsometer was used. The instrument is also used to investigate the influence of curved and rough surfaces which may occur due to the heating of the samples during the ellipsometric measurements.

Thermal Modelling and Experimental Validation in the Perspective of Tool Steel Laser Polishing

“…eral effects can occur such as Drude absorption [23], oxidation [24], or changes of surface roughness [25]. Schmid et al [26] demonstrated that the absorption of the liquid tool steel is also unknown due to the complexity of measuring this property. As a consequence, for the simulations, the absorption of the liquid was fitted based on the experimental measurements of the size of the melt pool and HAZ observed during the experiments.…”

Energy Efficient Laser Beam Welding of Metals with a Ultra-High Brightness Direct-Diode Laser System

“…All electrons in the valence-band contribute to this electron gas and influence the optical properties. These properties are defined by the components n and k of the refractive index which were computed following the procedure from Brueckner [22] and Schmid [23]:…”