Laser processing apparatus and laser irradiation method

A laser processing apparatus for reducing a magnetic domain size of a grain-oriented electrical steel sheet by focusing a laser beam on the grain-oriented electrical steel sheet and scanning the grain-oriented electrical steel sheet in a scanning direction with the laser beam, the laser processing apparatus comprising:

• a laser oscillator emitting the laser beam;
• and
• a laser irradiation unit applying the laser beam transmitted from the laser oscillator to the grain-oriented electrical steel sheet,
• wherein the laser irradiation unit has a structure providing an intensity distribution of the laser beam focused on the grain-oriented electrical steel sheet on a cross-section in a direction perpendicular to the scanning direction on the grain-oriented electrical steel sheet so as to satisfy Ib/Ia≦2, where, when an integral of the intensity distribution is calculated from a centroid of the intensity distribution in each of a first direction and a second direction which are both perpendicular to the scanning direction, Ra1 is a distance between the centroid of the intensity distribution and a position at which an intensity integration value from the centroid of the intensity distribution in the first direction is 43% of a total intensity integration value, Ra2 is a distance between the centroid of the intensity distribution and a position at which an intensity integration value from the centroid of the intensity distribution in the second direction is 43% of the total intensity integration value, a beam intensity Ia, is an intensity corresponding to the Ra1, the beam intensity Ia2 is an intensity corresponding to the Ra2, Ia is an average value of the beam intensity Ia1 and the beam intensity Ia2 and Ib is a beam intensity of the laser beam at the centroid of the intensity distribution.