Abstract: An apparatus and method for detecting when a hole has been drilled through a workpiece by way of a pulse laser drilling process having a machine control for controlling whether the pulse laser drill emits laser pulses. The apparatus detects the laser pulse and produces an output signal representative thereof. The output signal is clipped and compared to a first reference signal for producing a compared output signal when the clipped output signal is greater than the first reference signal. The compared output signal triggers an enabling output signal representative of a pulse having a predetermined interval. The apparatus also detects reflected radiation from an entrance of the hole being drilled to produce an output signal which is then clipped and compared to a second reference signal to produce a disabling output signal when the output signal representative of the reflected radiation is greater than the second reference signal.

Abstract: In the invention, a light beam is scanned along a surface bearing data, such as a serial number. Reflected light is measured and processed for character recognition. The invention wobbles or dithers the light beam during the scan, and takes reflectivity measurements several times within a region on the surface, the region being called a pixel. This procedure enhances the reflectivity signature of edges, thus improving the ability to recognize characters.