Laser marking method and system
View Patent ↗A laser marking method and system, and laser marked object are disclosed. The method includes directing a pulsed laser beam towards an object such that an interface between an oxidized layer and non-oxidized substrate is in a mark zone of the pulsed laser beam, and scanning the pulsed laser beam across the object in a predetermined pattern to create a mark having an L value of less than 40 and a surface roughness that is substantially unchanged compared to adjacent unmarked areas. The system includes a fiber laser generating amplified pulses that are directed towards a galvo-scanner and focusing optic, while the object includes an oxidized surface layer, an underlying non-oxidized substrate, and a mark having an L value of less than 40 with substantially unchanged roughness features.
1. A method of marking an object with a pulsed laser beam having a repetition rate of between 10 and 1000 kHz and an average power of less than 20 W, comprising:
directing the pulsed laser beam to the object such that a sub-surface interface between an oxidized surface layer and underlying non-oxidized substrate of the object is in a mark zone of the pulsed laser beam, and;
scanning the laser beam and object relative to each other in a predetermined pattern such that a mark is created below the surface of the object and into the underlying substrate;
wherein the mark zone is defined by an ablation threshold offset from a focal plane of the pulsed laser beam and a marking threshold offset from the focal plane of the pulsed laser beam;
wherein the pulses of the pulsed laser beam have a pulse width between about 0.8 ns and 2.0 ns.
2. The method of claim 1 wherein the object is anodized aluminum.
3. The method of claim 1 wherein the overlap of each pulse in the direction of scanning is 80% or more.
4. The method of claim 1 wherein the peak power of the pulsed laser beam is greater than 1 kW.
5. The method of claim 1 wherein the pulsed laser beam is substantially diffraction limited.
6. The method of claim 1 wherein the diameter of the pulsed laser beam in the mark zone is between 25 and 100 μm.
7. The method of claim 1 wherein said mark zone has a frustum shape.
8. The method of claim 1 wherein the predetermined pattern includes a spacing distance between adjacent scan paths of less than 20 μm.
9. The method of claim 8 wherein a spacing distance at about 20 μm or larger is destructive to the surface of the object.
10. The method of claim 1 wherein the overlap of each pulse in the direction of scanning is maintained above a scan spacing threshold percentage or below a scan spacing threshold distance so as to prevent destructive effects to the surface of the object.
11. The method of claim 1 wherein the pulsed laser beam is provided by a fiber laser comprising:
a diode-pumped solid state laser for generating a pulsed seed signal, and;
a diode-pumped fiber amplifier for amplifying the pulsed seed signal emitted from said solid state laser.
12. The method of claim 11 wherein said fiber laser has greater than about 1 kW peak power, less than about 2 ns pulse width, and greater than about 1 MW/cm 2 peak intensity.
13. The method of claim 12 wherein said diode-pumped solid state laser has greater than about 1 kW peak power, less than about 2 ns pulse width, and greater than about 1 MW/cm 2 peak intensity.
14. The method of claim 1 wherein the pulsed laser beam is provided by a diode-pumped solid state laser.
15. The method of claim 1 wherein the mark zone precedes a waist of the pulsed laser beam so as to allow the oxidized surface layer to receive less peak intensity than the sub-surface interface and underlying non-oxidized substrate.
16. The method of claim 1 further comprising:
before impinging on the target object, converting the pulsed laser beam shape to have a significantly uniform intensity distribution across one or more axes transverse to a propagation path of the pulsed laser beam.
17. The method of claim 16 wherein the conversion of the pulsed laser beam occurs by directing the beam through a top-hat spatial filter.
18. The method of claim 1 wherein the mark that is created has an ‘L’ darkness value of less than 40 and the object upon which the mark is created has a surface roughness substantially similar to the surface roughness in an adjacent unmarked area.
19. The method of claim 1 wherein the mark that is created has an ‘L’ darkness value of less than 30 and the object upon which the mark is created has a surface roughness substantially similar to the surface roughness in an adjacent unmarked area.
20. A laser marking system, comprising:
a pulsed laser source for providing a laser beam;
a scanner for scanning the pulsed laser beam in a pre-determined pattern; and
a focusing optic for focusing the pulsed laser beam to a mark zone;
wherein the pulsed laser beam is capable of creating a mark having a darkness value of less than 40 below the surface of a metallic target such that the surface roughness of the metallic target in the marked area is substantially unchanged;
wherein the mark zone is defined by an ablation threshold offset from a focal plane of the pulsed laser beam and a marking threshold offset from the focal plane of the pulsed laser beam;
wherein the pulses of the pulsed laser beam have a pulse width between about 0.8 ns and 2.0 ns.
21. The laser marking system of claim 20 , wherein said pulsed laser beam is capable of creating a mark having a darkness value of less than 30.
22. The laser marking system of claim 20 , wherein said laser source is a pulsed laser with greater than about 1 kW peak power, less than about 2 ns pulse width, and greater than about 1 MW/cm2 peak intensity.
23. The laser marking system of claim 22 , wherein the focusing optic is an Fθ lens.
24. The laser marking system of claim 20 , wherein said laser source is a pulsed fiber laser.
25. The laser marking system of claim 20 , wherein said pulsed laser source comprises:
a pulsed seed laser for emitting seed pulses, and;
a fiber amplifier for amplifying the seed pulses emitted from said pulsed seed laser.
26. The laser marking system of claim 25 , wherein said pulsed seed laser comprises a diode laser, and wherein said fiber amplifier comprises a plurality of fiber amplifier stages.
27. The laser marking system of claim 25 , wherein said pulsed seed laser comprises a diode pumped microchip laser, and wherein said fiber amplifier comprises one or more fiber amplifier stages.
28. The laser marking system of claim 25 , wherein said pulsed seed laser comprises a mode locked fiber laser and pulse picker, and wherein said fiber amplifier comprises multiple fiber amplifier stages.
29. The laser marking system of claim 20 , wherein said laser source is a pulsed solid-state laser.
30. The laser marking system of claim 20 , wherein said pulsed laser source comprises a diode pumped solid state laser.