Autofocus feedback positioning system for laser processing

Abstract

The present invention provides a laser processing and autofocusing system that measures the position of the work-piece at the machining spot, to allow the laser processing of work-pieces which are not flat and have surface variations, with the autofocusing system being able to compensate for these variations. During laser machining, it is desirable to keep the laser focus at the same height with respect to the surface of the sample for the best possible machining quality. Not all samples are flat, though, and it thus becomes necessary to map the surface of the sample accurately and to correct the focusing of the laser beam on the fly. The system includes a processing laser beam directed onto the surface at normal incidence and a light line projected onto the surface in the vicinity of the area being machined but at an angle with respect to the surface normal. The focusing optics for the machining laser and light line generator are fixed relative to each other on a positioning stage. If the work-piece surface deflects up or down, the light line moves correspondingly in the horizontal plane with respect to the laser focal spot. This change is monitored on the imaging system and the change of position is used to drive a controller. A proportional voltage set-point is produced by the electronics for feedback to the controller which uses this voltage reference to move the positioning stage to correct accordingly so the focal point of the processing laser beam is once again positioned at the surface of the work-piece.