Absorption in laser drilling in percussion regime

This paper presents some new results concerning absorption measurements in laser drilling in percussion regime used in aeronautical engine industries. This process consists in the irradiation of a metallic target with a laser tuned in the MW.cm^-2 range (pulse duration in mus-ms range). The laser energy is absorbed by the surface for the heating, the melting and the vaporization of the target. This vapor spreads out and pushes the melt pool. In this case, the drilling is dominated by melt ejection induced by the pressure gradient between the irradiated area and the hole surroundings. Balance energy evaluation is an essential diagnostic to describe laser/matter interaction. Particularly, in laser drilling, the laser/target coupling is related to the penetration of the laser in the target due to the hole formation. Laser beam could be confined in the hole cavity. Measurements have been performed with HL201P laser from Trumpf and integrating sphere coupled with calibrated photodiode. Laser is focused on the target located at the center of the sphere.