Local absorptivity modulation of a 1 μm-laser beam through surface waviness

► Glancing absorptivity of 1 μm lasers across a wavy molten steel surface. ► Even low roughness causes strong, complex local absorptivity modulation. ► For moderate and high roughness shadow domains gradually lower absorptance. ► Important consequences for laser welding, cutting, drilling. ► Angle- and wavelength-dependent Fresnel-curves determine absorption at rough surfaces.