STUDY OF DYNAMIC ABSORPTIVITY AT 10.6 µm (CO₂) AND 1.06 µm (Nd-YAG) WAVELENGTHS AS A FUNCTION OF TEMPERATURE

Abstract
One of the main advantages of Nd-YAG lasers compared to CO₂ lasers consists of easy beam handling using optical silica fibers. However, up to now Nd-YAG applications for material processing were limited due to a rather low available mean output power (less than about 500 W). A Eureka project (termed "EU-226") which consequently aimed at developing the so called "High Power Solid State Laser (HPSSL)" capable of 1 to 3 kW, involved absorptivity studies results of which are given in this contribution. Metallic surfaces exhibit a higher absorptivity at 1.06 µm (Nd-YAG) than at 10.6 µm which improves the energy transfer with a Nd-YAG laser and decreases the thermal runaway. This was acertained by measurements of absorptivity as a function of temperature and by thermal cycle calculations. This permits laser surface hardening of steels without any coating or gas shielding, which prevents in particular pollution. Various materials, I. e. pure nickel, Inconel 718 and AISI 1045 steel, were studied, featuring in particular the influence of surface roughness, oxidation and initial absorptivity on laser-material interaction.