Abstract: A method for selectively operating on a substrate by radiation controlled and caused to scan a portion of the surface of an article in such a manner as to selectively produce changes in material at the substrate surface. Miniature explosions of small quantities of material, such as particles thereof, may be employed to erode or otherwise remove material from the surface of the substrate. The method may be carried out in a closed chamber having a controlled atmosphere or pumped free of air to effect control of an erosion process. In a specific embodiment, a narrow beam of collimated radiation effects a scanning movement across the substrate while synchronously controlling the operation of a beam generating mechanism to cause the narrow beam to selectively irradiate a select portion of the substrate surface producing a select physical change in select material of the substrate.

Abstract: Removing some of the insulating material between commutator bars of flat or cylindrical commutators, hereinafter referred to as "undercutting, " by exposing the commutator surface to one or more energy beams of a frequency and an energy level and for a time which are sufficient for removing the dielectric material to the desired degree without or substantially without removal of commutator bar material. The energy beam or beams may be arranged under an angle with respect to the perpendicular direction so that a certain amount of dielectric material is also removed from a zone underneath the edges of the commutator bars. A preferred high energy source is the CO.sub.2 laser. Preferably, the high energy beam is guided over the commutator surface to sequentially illuminate, e.g., by a scanning motion, at least all exposed dielectric surfaces.