METHOD AND APPARATUS FOR FOCUS POSITION CONTROL IN LASER BEAM PROCESSING

摘要

A method for focus position control in laser beam processing comprises the following steps: - imparting to the laser beam some minor focus oscillation that does not affect the process stability and processing quality, for the oscillatory displacement of the focus position, - detecting the laser-induced plasma by means of a sensor that generates a corresponding sensor signal, - determining the amplitude and phase of the sensor signal oscillation resulting from the focus oscillation, the amplitude and phase being representative of the deviation of the focus position from the optimum focus position, and - tracking the focus position in accordance with the deviation determined.