Patent ID: 7333255

Claim:
A laser processing device comprising: a laser beam source which emits a laser beam; a collimating unit which collimates rays of the laser beam emitted from the laser beam source to parallel rays; a condensing optical system which condenses the parallel rays of the laser beam in a medium; a first lens group which is arranged in the parallel rays between the collimating unit and the condensing optical system and moves along the optical axis direction of parallel rays, the first lens group including one or more lenses; a second lens group which is securely arranged in the parallel rays between the first lens group and the condensing optical system, and includes one or more lenses; and a moving unit which moves the first lens group in accordance with the refractive index of the medium in which the laser beam is condensed and the distance from a surface of the medium to a position where the laser beam is condensed, wherein a rear side focal length of the second lens group is arranged at least in the vicinity of an entrance pupil position of the condensing optical system.