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 first linearly polarized laser oscillator configured to emit the linearly polarized laser beam, or a second laser oscillator configured to emit a laser beam and a polarizing beam splitter configured to convert the laser beam into the linearly polarized laser beam,

wherein, the linearly polarized laser beam emitted from the first linearly polarized laser oscillator or the second linearly polarized laser oscillator with the polarizing beam splitter is configured to be focused on the grain-oriented electromagnetic steel sheet in a linearly polarized state where 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 higher than 45° and equal to or lower than 90° on a surface of the grain-oriented electromagnetic steel sheet, the linear polarization direction being a direction to which the linearly polarized laser beam is polarized,

wherein the linearly polarized laser beam has a degree of polarization,

wherein the degree of polarization=PW1/(PW1+PW2), and

wherein the degree of polarization >=0.9 and the degree of polarization <1.0,

where PW1 represents a power of linearly polarized component and PW2 represents a power of an orthogonal component.

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 ≤1.19  (1).

3. The laser processing apparatus according to claim 2 ,

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

4. The laser processing apparatus according to claim 3 ,

wherein the first laser oscillator or the second laser oscillator is a CO 2 laser.

5. 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.

6. 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.

7. The laser processing apparatus according to claim 2 ,

wherein the first laser oscillator or the second laser oscillator is a CO 2 laser.

8. The laser processing apparatus according to claim 7 ,

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.

9. 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.

10. The laser processing apparatus according to claim 1 ,

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

11. The laser processing apparatus according to claim 10 ,

wherein the first laser oscillator or the second laser oscillator is a CO 2 laser.

12. The laser processing apparatus according to claim 11 ,

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.

13. The laser processing apparatus according to claim 10 ,

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.

14. The laser processing apparatus according to claim 1 ,

wherein the first laser oscillator or the second laser oscillator is a CO 2 laser.

15. The laser processing apparatus according to claim 14 ,

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.

16. 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.

17. The laser processing apparatus according to claim 1 , wherein one or more of laser irradiation devices comprises:

a λ/2 plate configured to adjust a linear polarization direction of the linearly polarized laser beam by changing its rotational angle;

a metallic mirror configured to squeeze and adjust a beam diameter of the linearly polarized laser beam adjusted by the λ/2 plate in a sheet width direction of the grain-oriented electromagnetic steel sheet;

a polygon mirror or a galvano mirror configured to scan the linearly polarized laser beam which is squeezed and adjusted by the metallic mirror on the grain-oriented electromagnetic steel sheet along the sheet width direction thereof; and

a parabolic mirror configured to squeeze and adjust the beam diameter of the linearly polarized laser beam reflected by the polygon mirror or the galvano mirror in a rolling direction of the grain-oriented electromagnetic steel sheet.