Patent ID: 7732730

Claim:
A laser processing apparatus for forming a modified region which functions as a starting point for cutting within an object to be cut, comprising: a stage adapted for mounting the object; a laser source for emitting a pulsed laser light along an optical axis, the object being transparent to the pulsed laser light; an observation light source for illuminating a surface of the object with a visible observation light having a different wavelength from that of the laser light; an image pick-up element for imaging the surface of the object illuminated by the observation light source; a converging lens for converging the pulsed laser light emitted from the laser source within the object mounted on the stage, to form the modified region at a position of the converging point of the pulsed laser; a controller for controlling movement of at least one of the converging lens and the stage to focus the observation light through the converging lens at a reference position on the surface of the object, to thereafter move at least one of the converging lens and the stage in a direction along the optical axis of the pulsed laser light by an amount of movement corresponding to predetermined displacement data for determining a position of the converging point of the pulsed laser light to be arranged within the object, to cause the converging point of the pulsed laser light to be positioned within the object at a location spaced from the reference position by the amount of movement corresponding to the predetermined displacement data, and to thereafter to initiate irradiation by the pulsed laser light and movement of the stage along a line along which the object is intended to be cut in order to form a modified region within the object along the line along which the object is intended to be cut.