A laser scriber with a self-correcting mechanism comprises a laser scribing unit, a detection unit, a control unit and a drive unit. A first waveform generator generates a first predetermined waveform and a second waveform generator generates a second predetermined waveform. Nodes that are in separate \u201cextended neighborhoods\u201d are permitted to transmit their beacons simultaneously without risking beacon collisions. The method further comprises illuminating a portion of the fill layer with electromagnetic radiation, hereby producing a exposed portion and an unexposed portion, the portions being separated by an interface substantially parallel with the first main surface of the substrate. In accordance with an image forming apparatus according to the invention, in a scanning optical system using an imaging lens or an imaging mirror, influences against optical characteristics following an environmental fluctuation or a change with time can be reduced.