Abstract: In the perforation of sheet material by light energy, a continuous focused laser beam is reflected from different locations along the beam axis to provide separate pulsed beams and the beams are issued onto the sheet material with the same beam cross-sectional area. In one aspect, the lengths of respective different light paths for conveyance of light from the point of focus of the laser to final image locations are made equal. In another aspect, different focusing elements may be included in light paths to provide for sameness of beam cross-sectional area at the final image locations. The light paths are preferably provided in part by light conducting apparatus having light-reflective elements mounted for movement, such that different perforation matrices may be readily attained.

Abstract: In providing perforation uniformity both in the spacing between multiple rows of perforations in sheet material and in the spacings among perforations within each row, a common laser beam is shared among the rows, being directed to the sheet material through a common focusing element for each adjacent pair of rows. In conducting the laser beam to each such common focusing element, a pair of modified beams is derived from the laser beam, each modified beam having light ray content divergent about an axis of symmetry thereof which is parallel to the optical axis of the focusing element.