Beam parameter product (bpp) control by varying fiber-to-fiber angle

1. An apparatus, comprising:

a laser system including a first fiber having an output end and situated to propagate a first laser beam with a first beam parameter product (bpp) and a second fiber having an input end spliced to the output end of the first fiber at a fiber splice so as to receive the first laser beam and to form a second laser beam having a second bpp that is greater than the first bpp;

wherein the fiber splice is a fusion splice having a selected tilt angle that produces a selected bpp increase portion of the difference between the first bpp and the second bpp.

2. The apparatus of claim 1 , wherein the first fiber is a first gain fiber and the second fiber is a second gain fiber.

3. The apparatus of claim 2 , wherein the second gain fiber has a core diameter that is larger than a core diameter of the first gain fiber.

4. The apparatus of claim 1 , wherein the first fiber is a final gain fiber of the laser system and the second fiber is a passive output fiber.

5. The apparatus of claim 1 , wherein the first fiber is a passive fiber and the second fiber is a system delivery fiber.

6. The apparatus of claim 1 , wherein the selected tilt angle is between 0.2 degrees and 5.0 degrees based on the selected bpp increase portion.

7. The apparatus of claim 1 , wherein the selected tilt angle corresponds to an angle between a surface of the output end of the first fiber and a surface of the input end of the second fiber.

8. The apparatus of claim 1 , wherein the selected tilt angle of the fusion splice corresponds to an angle between a longitudinal axis of the first fiber at the output end and a longitudinal axis of the second fiber at the input end.

9. The apparatus of claim 1 , wherein the selected tilt angle corresponds to a first angle between a surface of the output end of the first fiber and a plane perpendicular to a longitudinal axis of the first fiber at the output end, a second angle between a surface of the input end of the second fiber and a plane perpendicular to a longitudinal axis of the second fiber at the input end, or both the first and second angles.

10. The apparatus of claim 1 , wherein the output end of the first fiber and the input end of the second fiber include respective cleaved surfaces.

11. The apparatus of claim 8 , wherein the selected tilt angle is between 1.5 degrees and 2.0 degrees.

12. The apparatus of claim 1 , wherein the selected bpp increase portion of the increase between the first bpp and the second bpp is between 0.95 mm-mrad and 1.55 mm-mrad.

13. The apparatus of claim 1 , wherein the laser system is configured to generate the first laser beam having continuous power of between 800 W and 4 kW.

14. The apparatus of claim 1 , wherein the selected bpp portion of the increase between the first bpp to the second bpp occurs at a location downstream of the splice.

15. The apparatus of claim 1 , wherein the fiber splice is positioned between fiber gain sections.

16. The apparatus of claim 15 , wherein the fiber splice is positioned after a final oscillator.

17. The apparatus of claim 15 , wherein the fiber splice is positioned before a fiber amplifier.

18. The apparatus of claim 1 , further comprising an alignment assistance mechanism configured to assist with the alignment of the first and second fibers by coupling light into the first fiber and detecting the amount of light received by the second fiber.

19. The apparatus of claim 18 , wherein the alignment assistance mechanism further comprises one or more cameras allowing a magnified view of respective end portions of the first fiber and the second fiber.

20. The apparatus of claim 1 , wherein the bpp increase portion is zero where the selected tilt angle is 0 degrees.