Abstract
Abstract
The absorptivity is a major parameter in laser-matter interaction. It can be measured by different methods (thermal or optical). The already known integrating sphere method is generally used with spheres whose choice of dimensions and architecture is not discussed in the literature. The influence of the parameters of the sphere (size of the sphere, position of the photodiode on the sphere, distance of the photodiode from the sphere, opening of the passage of the laser, distance from sample to the sphere, presence of a baffle in front of the photodiode, sample angle, coating materials) was tested with a mirror of known reflectivity. This study has demonstrated that it is possible to use small integrating spheres for absorptivity measurements. These spheres are home-made by additive manufacturing from a polymer, with the inner walls coated with BaSO4. The optimum experimental conditions for these small spheres are defined, particularly the angle sample. The absorptivity of various materials in the solid state and powder bed was measured for four wavelengths. These measurements were carried out for three sizes of spheres and confirmed the literature results (for example, the absorptivity is measured at 80% for copper at blue wavelength). This small sphere will be adapted to in-situ measurement, particularly in the Laser Powder Bed Fusion process whatever wavelength, particularly new green or blue laser sources, and material.