Processing method using laser beam

摘要

A processing method using a laser beam, which can locate the focus point of a laser beam ( 82 ), sufficiently easily and promptly, at a position of a predetermined depth (D) below the face of a workpiece ( 34 ). The spacing between a focusing optical system ( 78 ) and the face of the workpiece when the laser beam is focused onto the face of the workpiece is adopted as a reference spacing (BL), and the spacing (SL) between the focusing optical system and the face of the workpiece is set based on a set equation taking into consideration the numerical aperture of the focusing optical system and the refractive index of the workpiece in combination with the reference spacing (BL).