Varying beam parameter product of a laser beam
View Patent ↗An optical delivery waveguide for a material laser processing system includes a small lens at an output end of the delivery waveguide, transforming laser beam divergence inside the waveguide into a spot size after the lens. By varying the input convergence angle and/or launch angle of the laser beam launched into the waveguide, the output spot size can be continuously varied, thus enabling a continuous and real-time laser spot size adjustment on the workpiece, without having to replace the delivery waveguide or a process head. A divergence of the laser beam can also be adjusted dynamically and in concert with the spot size.
1. A laser beam delivery waveguide assembly for outputting a variable output spot size laser beam, the laser beam delivery waveguide assembly comprising:
a step-index delivery optical waveguide having first and second ends for guiding a laser beam from the first end to the second end; and
first and second graded-index optical elements fused to the first and second ends, respectively, for coupling the laser beam into the first end and out of the second end, respectively, of the step-index delivery optical waveguide, wherein
the step-index delivery optical waveguide has a non-varying diameter along its length,
the first graded-index optical element has a non-varying diameter along its length, and
the second graded-index optical element has a non-varying diameter along its length.
2. The laser beam delivery waveguide assembly of claim 1 , further comprising:
first and second end caps fused to the first and second graded-index optical elements, respectively, for transmitting the laser beam to the first graded-index optical element and from the second graded-index optical element, respectively.
3. The laser beam delivery waveguide assembly of claim 1 , wherein the first graded-index optical element is offset laterally, with respect to a core of the step-index delivery optical waveguide, for launching the laser beam to produce a vortex beam at an output.
4. The laser beam delivery waveguide assembly of claim 1 , wherein
at least one of the first or second graded-index optical elements is of quarter-pitch length or an odd multiple thereof, and
at least one of the first or second graded-index optical elements has a focal length no greater than 10 mm.
5. The laser beam delivery waveguide assembly of claim 1 , wherein
at least one of the first or second graded-index optical elements is not of quarter-pitch length or an odd multiple thereof, and
at least one of the first or second graded-index optical elements has a refractive index profile such that, when used in a length of one-quarter pitch, would yield a focal length of no greater than 10 mm.
6. The laser beam delivery waveguide assembly of claim 1 , further comprising:
a shifter for providing a variable lateral displacement between the laser beam and an optical axis of the first end of the step-index delivery optical waveguide.
7. The laser beam delivery waveguide assembly of claim 1 , further comprising:
a shifter for laterally displacing an input beam from an optical axis by more than a radius of the input beam, thereby creating an annular near-field spot at an output.
8. The laser beam delivery waveguide assembly of claim 1 , further comprising:
a shifter for tilting and laterally displacing an input beam,
wherein the tilting is noncollinear with the lateral displacement, thereby producing a vortex beam at an output.
9. The laser beam delivery waveguide assembly of claim 1 , further comprising:
a shifter including a laterally displaceable lens or optical wedge for laterally displacing the laser beam.
10. The laser beam delivery waveguide assembly of claim 9 , further comprising:
a flexure mount for displaceably mounting the laterally displaceable lens or the optical wedge.
11. The laser beam delivery waveguide assembly of claim 1 , wherein the step-index delivery optical waveguide includes a core that has a non-circular cross-section for facilitating formation of a substantially uniform radial distribution of intensity of the laser beam at the second end, thereby facilitating uniform distribution of ray angles at a first laser beam waist.
12. The laser beam delivery waveguide assembly of claim 11 , wherein the non-circular cross-section is one of: a square, a rectangular, triangular, hexagonal, octagonal, D-shaped, rippled, cusped, or a star shape.
13. The laser beam delivery waveguide assembly of claim 1 , wherein the step-index delivery optical waveguide includes a cladding that surrounds a core,
the cladding having a diameter of at least 250 micrometers.
14. The laser beam delivery waveguide assembly of claim 13 , wherein the cladding comprises a SiO2 cladding.
15. The laser beam delivery waveguide assembly of claim 1 , wherein a length of the step-index delivery optical waveguide between the first and second ends is at least 1 m.
16. The laser beam delivery waveguide assembly of claim 1 , wherein the step-index delivery optical waveguide comprises a polarization-maintaining waveguide, a polarizing waveguide, a chiral waveguide, or a spun waveguide for controlling polarization of the laser beam.
17. The laser beam delivery waveguide assembly of claim 1 , wherein the step-index delivery optical waveguide is one of: a double-clad waveguide, a multi-clad waveguide, a photonic-crystal waveguide, or a micro-structured waveguide.
18. The laser beam delivery waveguide assembly of claim 1 , further comprising:
a vibrating unit, coupled to the step-index delivery optical waveguide, for vibrating the step-index delivery optical waveguide when the laser beam is launched therein.
19. The laser beam delivery waveguide assembly of claim 18 , wherein the vibrating unit is one of: an acoustic transducer, an ultrasonic transducer, or a mechanical vibrator.
20. A method for outputting a variable output spot size laser beam, the method comprising:
guiding, by a step-index delivery optical waveguide having first and second ends, a laser beam from the first end to the second end; and
coupling, by first and second graded-index optical elements fused to the first and second ends, respectively, the laser beam into the first end and out of the second end, respectively, of the step-index delivery optical waveguide, wherein
the step-index delivery optical waveguide has a non-varying diameter along its length,
the first graded-index optical element has a non-varying diameter along its length, and
the second graded-index optical element has a non-varying diameter along its length.