Laser processing apparatus

1. A laser processing apparatus for refining magnetic domains of a grain-oriented electromagnetic steel sheet by setting a linearly polarized laser beam to be focused on the grain-oriented electromagnetic steel sheet and scanned in a scanning direction, the laser processing apparatus comprising:

a laser oscillator configured to emit the linearly polarized laser beam, or a laser oscillator configured to emit a laser beam and a polarizer configured to convert the laser beam into the linearly polarized laser beam,

wherein an angle between a linear polarization direction of the linearly polarized laser beam focused on the grain oriented electromagnetic steel sheet and the scanning direction is equal to or higher than 0° and lower than 45° on a surface of the grain-oriented electromagnetic steel sheet and the scanning direction is substantially perpendicular to a transport direction of the grain-oriented electromagnetic steel sheet, and

wherein an incident angle ϕ of the laser beam into the surface of the grain-oriented electromagnetic steel sheet becomes 0° when an incident position of the laser beam is coincident with a center portion of a laser scanning width and the incident angle ϕ of the laser beam increases as the incident position of the laser beam approaches the end portions of the laser scanning width, and

wherein the laser beam has a degree of polarization defined as PW1/(PW1+PW2), a linearly polarized light having the degree of polarization of 0.9 or higher and lower than 1.0, wherein a power of a linearly polarized component is given by PW1 and a power of an orthogonal component is given by PW2.

2. The laser processing apparatus according to claim 1 ,

wherein a maximum incident angle ϕ MAX of the laser beam incident on the grain-oriented electromagnetic steel sheet satisfies the following conditional expression (1).

1/cos ϕ MAX ≤1.24  (1)

3. The laser processing apparatus according to claim 1 ,

wherein a wavelength of the laser beam focused on the grain-oriented electromagnetic steel sheet is 0.15 μm or higher and 7 μm or lower.

4. The laser processing apparatus according to claim 2 ,

wherein a wavelength of the laser beam focused on the grain-oriented electromagnetic steel sheet is 0.15 μm or higher and 7 μm or lower.

5. The laser processing apparatus according to claim 1 ,

wherein the laser oscillator is a fiber laser or a disk laser.

6. The laser processing apparatus according to claim 2 ,

wherein the laser oscillator is a fiber laser or a disk laser.

7. The laser processing apparatus according to claim 3 ,

wherein the laser oscillator is a fiber laser or a disk laser.

8. The laser processing apparatus according to claim 4 ,

wherein the laser oscillator is a fiber laser or a disk laser.

9. The laser processing apparatus according to claim 1 ,

wherein a shape of the laser beam focused on the grain-oriented electromagnetic steel sheet is an ellipse, and

a minor axis direction of the ellipse is perpendicular to the scanning direction.

10. The laser processing apparatus according to claim 2 ,

wherein a shape of the laser beam focused on the grain-oriented electromagnetic steel sheet is an ellipse, and

a minor axis direction of the ellipse is perpendicular to the scanning direction.

11. The laser processing apparatus according to claim 3 ,

wherein a shape of the laser beam focused on the grain-oriented electromagnetic steel sheet is an ellipse, and

a minor axis direction of the ellipse is perpendicular to the scanning direction.

12. The laser processing apparatus according to claim 4 ,

wherein a shape of the laser beam focused on the grain-oriented electromagnetic steel sheet is an ellipse, and

a minor axis direction of the ellipse is perpendicular to the scanning direction.