A laser irradiation apparatus is a laser irradiation apparatus including a plurality of laser light sources, the laser irradiation apparatus including a control unit configured to perform control with regard to laser emitted from the plurality of laser light sources, in which the control unit acquires characteristic information of each of the plurality of laser light sources, and performs a predetermined process according to each piece of acquired characteristic information.

A crystalline material processing method includes forming subsurface laser damage at a first average depth position to form cracks in the substrate interior propagating outward from at least one subsurface laser damage pattern, followed by imaging the substrate top surface, analyzing the image to identify a condition indicative of presence of uncracked regions within the substrate, and taking one or more actions responsive to the analyzing. One potential action includes changing an instruction set for producing subsequent laser damage formation (at second or subsequent average depth positions), without necessarily forming additional damage at the first depth position. Another potential action includes forming additional subsurface laser damage at the first depth position. The substrate surface is illuminated with a diffuse light source arranged perpendicular to a primary substrate flat and positioned to a first side of the substrate, and imaged with an imaging device positioned to an opposing second side of the substrate.