LENS POSITION CONTROL METHOD, LENS POSITION CONTROL APPARATUS, CUTTING METHOD, AND CUTTING APPARATUS

摘要

A lens position control method is disclosed. Either an objective lens or a master disc having a resist material film on its substrate is moved, thereby changing a distance between the objective lens and the master disc surface. A return laser beam transmitted through the objective lens and reflected by the master disc surface is detected by a photodetector. The movement of either of them is stopped when the master disc is located near a focal point of the objective lens and the return laser beam is detected. Limit data is rewritten to data corresponding to a position obtained by adding a movement permission amount smaller than a working distance of the objective lens to the stop position. When the return laser beam is not detected, the movement which changes the distance between them is stopped at a position corresponding to the limit data.