Laser surface treatment of materials by using CO2 laser beam at oblique incidence

The amount of the heat transferred to the workpiece is of high importance on the laser surface treatment. A possibility to increase the energy coupling efficiency by using oblique incidence of the laser beam is proposed. The drawback of oblique incidence technique consists in the deformation of the laser intensity profile on the irradiated surface at large incidence angles (70 degrees -80 degrees). This paper is dealing with a method to overcome this disadvantage: focusing the laser beam in an elliptical shape at normal incidence; using oblique incidence at large angles (70 degrees -80 degrees) a circular focused p-polarized spot is obtained. The absorption is (2.5-4) times enhanced and the focused spot on the surface has a circular shape. The use of oblique incidence of the laser beam allows another important advantage: the avoidance of the contamination of the focusing optics. The cladding experiments at 75 degrees incidence angle have been carried out at only 650 W laser power level. An improved cladding efficiency was obtained.