An apparatus and method for exposing the surface of a drum to patterned illumination from a pulsed laser source to form a dense, regular array of 3-D microstructures is provided. The method may include locating a mask relative to a target area, projecting a uniform line shaped laser beam through the mask to project an image including a plurality of features of the mask onto the target area, de-magnifying the image, rotating the drum continuously so the surface moves in a first direction perpendicular to the axis of rotation of the drum and simultaneously moving the projected beam 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 pulsed laser based on an angular position of the drum.