Patent ID: 8563893

Claim:
A laser processing apparatus for forming a modified region to become a cutting start point within a planar object to be processed by irradiating the object with first laser light while locating a converging point within the object; the apparatus comprising: a converging lens for converging the first laser light and second laser light to be reflected by a laser-light-irradiated surface irradiated with the first laser light in the object toward the object; driving means for actuating the converging lens along an optical axis direction thereof; astigmatism adding means for adding astigmatism to reflected light of the second laser light reflected by the laser-light-irradiated surface; a photodetector device for receiving the astigmatism-added reflected light of the second laser light reflected by the laser-light-irradiated surface in a split fashion and outputting respective output values corresponding to light quantities of reflected light components of the second laser light received in the split fashion; and control means for regulating the driving means such that the converging point of the first laser light is positioned at a predetermined distance from the laser-light-irradiated surface; wherein the second laser light is converged toward the object by the converging lens such as to have a converging point between a focal point of the converging lens and the converging lens; and wherein the control means regulates the driving means according to an arithmetic value acquired by subjecting the output values outputted from the photodetector device to a division by a sum of the output values and a predetermined arithmetic operation.