Cutting method using a laser having at least one ytterbium-based fiber, in which at least the power of the laser source, the diameter of the focused beam and the beam quality factor are controlled

1. A method of cutting a workpiece with a laser beam, wherein laser beam generation means comprising at least one ytterbium-containing fiber and having a wavelength between 1 and 4 μm, are used to generate the laser beam, and wherein the laser beam is selected so as to have:

a power of less than 100 kW;

a power density of at least 1 MW/cm 2 ;

a focused beam diameter of at least 0.1 mm; and

a beam parameter product (BPP) of less than 10 mm·mrad.

2. The method of claim 1 , wherein the fiber is formed from an ytterbium-doped core clad with silica.

3. The method of claim 1 , wherein the laser beam generated by the ytterbium-based fiber has a wavelength of between 1.04 and 3 μm.

4. The method of claim 3 wherein the laser beam generated by the ytterbium-based fiber has a wavelength of about 1.07 μm.

5. The method of claim 1 , wherein the quality factor (BPP) of the laser is between 1 and 8 mm·mrad.

6. The method of claim 5 wherein the quality factor (BPP) of the laser is between 2 and 6 mm·mrad.

7. The method of claim 1 , wherein the laser beam has a power of between 0.1 and 40 kW.

8. The method of claim 7 , wherein the laser beam has a power of between 0.5 and 15 kW.

9. The method of claim 1 , wherein the laser beam has a power density between 1.5 and 20 MW/cm 2 .

10. The method of claim 1 , wherein the focused beam diameter is between 0.1 mm and 0.50 mm.

11. The method of claim 10 , wherein the focused beam diameter is between 0.13 and 0.40 mm.

12. The method of claim 1 , wherein the laser beam has a Raleigh length (Zr) of between 1 and 10 mm.

13. The method of claim 12 , wherein the laser beam has a Raleigh length (Zr) of between 2 and 7 mm.

14. The method of claim 1 , wherein the beam is used with an angular aperture (θ) of between 0.25° and 5° and an angle α of between 1.25° and 8°, corresponding to the angle defines by the diameter (2W 0 ) of the focused laser beam divided by the thickness (E) of the metal sheet or plate, these being such that the sum of the angles (α+θ) is between 1.5° and 8°.

15. The method of claim 1 , wherein the assist gas for the laser beam is chosen from nitrogen, helium, argon, oxygen, CO 2 and mixtures thereof, and optionally also contains one or more additional compounds chosen from H 2 and CH 4 .

16. The method of claim 1 , wherein the workpiece to be cut has a thickness of between 0.25 and 30 mm.

17. The method of claim 16 , wherein the workpiece to be cut has a thickness of between 0.40 and 20 mm.

18. The method of claim 2 , wherein the laser beam generated by the ytterbium-based fiber has a wavelength of between 1.04 and 3 μm.

19. The method of claim 18 , wherein the quality factor (BPP) of the laser is between 1 and 8 mm·mrad.

20. The method of claim 19 , wherein the laser beam has a power of between 0.1 and 40 kW and a power density between 1.5 and 20 MW/cm 2 .

21. The method of claim 20 , wherein the focused beam diameter is between 0.1 mm and 0.50 mm.

22. The method of claim 21 , wherein the laser beam has a Raleigh length (Zr) of between 1 and 10 mm.

23. The method of claim 22 , wherein the beam is used with an angular aperture (θ) of between 0.25° and 5° and an angle α of between 1.25° and 8°, corresponding to the angle defines by the diameter (2W 0 ) of the focused laser beam divided by the thickness (E) of the metal sheet or plate, these being such that the sum of the angles (α+θ) is between 1.5° and 8°.

24. The method of claim 23 , wherein the assist gas for the laser beam is chosen from nitrogen, helium, argon, oxygen, CO 2 and mixtures thereof, and optionally also contains one or more additional compounds chosen from H 2 and CH 4 .

25. The method of claim 24 , wherein the workpiece to be cut has a thickness of between 0.25 and 30 mm.