METHOD AND APPARATUS FOR LASER PROCESSING THE SURFACE OF A DRUM

摘要

A method for exposing the surface of a drum to patterned illumination from a pulsed laser source at a suitable energy density in order to cause ablation of the surface to form a dense, regular array of 3-D microstructures, comprising the steps of: locating a mask containing a line of different features on a fixed pitch relative to a target area; projecting a uniform line shaped laser beam through the mask in order to project an image made up of a multiplicity of the features on the mask onto the target area; de- magnifying the image carried by the beam between the mask and the target area; locating the surface of the drum for ablation in the target area; rotating the drum continuously so the surface moves in a first direction perpendicular to the axis of rotation of the drum and also simultaneously moving the projected beam with respect to the drum in a second direction parallel to the axis of rotation of the drum; tilting the projected array of microstructures to correspond to the helical path followed by the laser beam on the drum surface; and controlling the firing of the pulsed laser in relation to the exact angular position of the drum in the target area. Apparatus for carrying out the method is also described.