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EP-4429048-B1 - METHOD FOR SYMMETRIZING SINGLE-SIDED PUMP LASER PROFILES

EP4429048B1EP 4429048 B1EP4429048 B1EP 4429048B1EP-4429048-B1

Inventors

  • HUBBARD, WILLIAM J.
  • GORVEATT, William J.
  • TOBEY, Alan E.

Dates

Publication Date
20260506
Application Date
20231220

Claims (10)

  1. A method (300) for making a single-sided pumped laser device comprising: determining (304) an absorption coefficient for a laser medium body; determining (308) divergence angles of pump light from a laser pump to be directed at a side of the laser medium body; determining (308) initial relative spacings of at least one reflector for the pump light with respect to the laser medium body and the laser pump; generating (310) a merit function defining a desired absorption profile of the pump light passing through the laser medium body; using a processor and an associated memory to operate (314) an optical model based on the merit function and the determined absorption coefficient, divergence angles and initial relative spacings to determine the following: a curvature of the at least one reflector (314), and adjusted relative spacings among the laser medium body (316), the laser pump, and the at least one reflector; and assembling (318) the laser medium body, the laser pump, and the at least one reflector according to the determined curvature of the at least one reflector and the adjusted relative spacings to make the single-sided pumped laser device, wherein the method is characterized in that the single-sided pumped laser device comprises ancillary reflectors (E) that are configured to reflect residual pump light, which is reflected by the at least one reflector (D), to the laser medium body (C) along an axis, which is perpendicular to an emission axis of the laser pump (A).
  2. The method (300) according to Claim 1 wherein the merit function comprises a plurality of target absorption values defining the desired absorption profile.
  3. The method (300) according to Claim 2 wherein the optical model determines a plurality of computed absorption profiles, with each computed absorption profile comprising a plurality of computed absorption values corresponding to the plurality of target absorption values.
  4. The method (300) according to Claim 3 wherein the optical model determines the plurality of computed absorption profiles while varying curvature of the at least one reflector and varying relative spacings among the laser medium body, the laser pump and the at least one reflector.
  5. The method (300) according to Claim 3 wherein the merit function compares, for each computed absorption profile, the plurality of computed absorption values to the plurality of target absorption values.
  6. The method (300) according to Claim 5 wherein the merit function determines, for each computed absorption profile, a difference between the plurality of computed absorption values and the corresponding plurality of target absorption values, with the differences for each computed absorption profile being summed together to define a respective merit function value.
  7. The method (300) according to Claim 6 wherein the optical model defines a plurality of respective merit function values ranging from high to low, with the single-sided pumped laser device being assembled using the curvature of the at least one reflector and the relative spacings among the laser medium body, the laser pump and the at least one reflector for the merit function value having the lowest value.
  8. The method (300) according to Claim 1 wherein the laser pump comprises a laser diode.
  9. A non-transitory computer readable medium for operating a computing device comprising a display and processor coupled to the display, and with the non-transitory computer readable medium having a plurality of computer executable instructions for causing the processor to perform the method according to Claim 1.
  10. The non-transitory computer readable medium according to Claim 9 wherein the desired absorption profile of the pump light is symmetrical to a centerline of the laser medium body.

Description

Technical Field The present disclosure relates to laser devices, and more particularly, to a method for making a single-sided pumped laser device having a symmetrical absorption pump profile within a laser medium body. Background Laser devices have grown in usefulness, particularly in industrial, medical and military applications. Diode pumped laser devices are power efficient and solid-state with a long shelf-life. Laser devices may be single pumped on one side of the laser medium body, or double pumped along multiple axes of the laser medium body to increase radial symmetry. A single pumped laser device as compared to a double pumped laser device is more cost efficient since less components are required. However, a drawback of a single pumped laser device is that the pump light distribution within the laser medium body can lead to an asymmetric pattern relative to a centerline (i.e., longitudinal axis) of the laser medium body. Asymmetry of the pump light distribution within the laser medium body can be inefficient and lead to sub-optimal laser mode performance. Examples for single-sided pumped laser devices are disclosed in Walmsley Ian A: "Non-edge-ray design: improved optical pumping of lasers", Optical Engineering, vol. 43, no. 7, 1 July 2004, page 1511; Koshel R ET AL: "Diode Side Pumping of an Nd:YAG Laser Rod with a Nonimaging Pump Cavity", International Optical Design Conference, 1 January 1994, page NISL304; Koshel R ET AL: "Modeling of the gain distribution for diode pumping of a solid-state laser rod with nonimaging optics", Applied Optics, vol. 32, no. 9, 20 March 1993, page 1517; LIANG ET AL: "Diode pumping of a solid-state laser rod by a two-dimensional CPC-elliptical cavity with intervening optics", OPTICS COMMUNICATIONS, ELSEVIER, AMSTERDAM, NL, vol. 275, no. 1, 10 May 2007, pages 104-115; and Yi Jonghoon ET AL: "Diode-Pumped Nd: YAG Rod Laser with Single-Side Pumping Geometry", Journal of the Korean Physical Society, vol. 57, no. 2(1), 13 August 2010, pages 355-358. Further examples for single-sided pumped laser devices are disclosed in US 8 320 425 B1 and US 2023/028158 A1. Summary The invention is defined by independent claims 1 and 9. Further embodiments of the invention are defined by the dependent claims. An example method for making a single-sided pumped laser device may include determining an absorption coefficient for a laser medium body, determining divergence angles of pump light from a laser pump to be directed at a side of the laser medium body, and determining initial relative spacings of at least one reflector for the pump light with respect to the laser medium body and the laser pump. A merit function defining a desired absorption profile of the pump light passing through the laser medium body may be generated. The method may further include using a processor and an associated memory to operate an optical model based on the merit function and the determined pump light absorption coefficient, divergence angles and initial relative spacings to determine a curvature of the at least one reflector, and adjusted relative spacings among the laser medium body, the laser pump, and the at least one reflector. The laser medium body, the laser pump, and the at least one reflector may be assembled according to the determined curvature of the at least one reflector and the adjusted relative spacings to make the single-sided pumped laser device. The merit function may include a plurality of target absorption values defining the desired absorption profile. The optical model may determine a plurality of computed absorption profiles, with each computed absorption profile comprising a plurality of computed absorption values corresponding to the plurality of target absorption values. The optical model may determine the plurality of computed absorption profiles while varying curvature of the at least one reflector and varying relative spacings among the laser medium body, the laser pump and the at least one reflector. The merit function may compare, for each computed absorption profile, the plurality of computed absorption values to the plurality of target absorption values. The merit function may determine, for each computed absorption profile, a difference between the plurality of computed absorption values and the corresponding plurality of target absorption values, with the differences for each computed absorption profile being summed together to define a respective merit function value. The optical model may define a plurality of respective merit function values ranging from high to low, with the single-sided pumped laser device being assembled using the curvature of the at least one reflector and the relative spacings among the laser medium body, the laser pump and the at least one reflector for the merit function value having the lowest value. The laser pump may include a laser diode. The laser medium body may include one of a laser rod having a cylindrical shape and a laser slab having