Abstract: In treating the surface of a material with laser energy by sweeping a laser beam over the surface, a substantial uniformity of energy delivery is achieved across a major portion of the transverse width of the beam by using an unfocussed beam of a ring mode configuration and preferably one having an outer ring with at least some degree of interior fill as is achieved by a laser beam continuing TEM.sub.00 and TEM.sub.01 * modes. The specification discusses various beam configurations. The specification introduces the concept of "exposure integration" which is a function not only of the beam profile in the sweep direction but of the rate of sweep. An exposure duration for any scanned point of not more than 10 milliseconds is suggested. The application of the invention is particularly described with reference to marking the surface of paper.

Abstract: A laser beam is used to mark a longitudinally moving web of paper both at intervals along its length and at plural locations across its width so that each of the sheets finally cut from the web bears a mark. The web passes over a cylinder having windows bearing masks carrying a logo or the like to be marked on the web. Mirrors are arranged on a drum assembly coaxially located in the cylinder to rotate therewith. The mirrors are disposed in helical sets extending along the axis of the drum to successively intercept a laser beam directed parallel to the axis of the drum and to reflect the beam to successive mask windows. The mirrors are plane mirrors set at 45.degree. to the axis and cause the beam to scan the mask in the circumference direction. The beam is collimated but not focussed and has a diameter that encompasses the transverse width of the mask. A ring mode laser beam is preferred.

Abstract: A hydraulic noise attenuator of the type utilizing a tubular casing having an inlet and outlet end, a perforated tube extending through the casing, the ends of the tube being secured in the inlet and outlet ends of the casing, portions of the tube adjacent at least the secured outlet end thereof, being encompassed by sound-absorbing material means being provided to reflect sound waves against the sound-absorbing material to enhance the attenuation at the lower frequencies.