Fig. 1. Edge-emitting laser (EEL) and VCSEL structures^[9]. Unlike optical coating on the facets of the EEL, the VCSEL has a COD-free DBR facet grown via epitaxy.

Fig. 2. Resonator of a diode side-pumped Nd:YAG laser.

Fig. 3. Conventional LD pump cavities. Odd-numbered LD arrays are aligned to avoid reciprocal damage and an internal reflector is introduced to improve absorption and efficiency.

Fig. 4. Fluorescence distribution from an NG CEO REA22 pump module^[18]. Pumping beam traces from seven directions can be clearly found and the beam profile has no circular symmetry.

Fig. 5. VCSEL resonator principle. The surface of the VCSEL chip is highly reflective and external photon injection will not cause any damage in the emitters.

Fig. 6. VCSEL emitting facet photo from an actual chip taken by the authors.

Fig. 7. (a) VCSEL in CoS package on a metallized AlN submount with a rectangular emitting area and (b) laser bar assembly with a linear emitting line between the clamping electrodes.

Fig. 8. Single pass pumping and absorption simulation at different distances from the (a) laser bar and (b) VCSEL.

Fig. 9. Absorption spectrum of the Nd:YAG with peak absorption at 808.5 nm. Absorption data were provided by Beijing Opto-Electronics Technology Co., Ltd. and the figure was drafted by the authors for reference only.

Fig. 10. Pump diode alignment around the Nd:YAG rod with uniform wavelength per circle. Each circle is required to be with the same wavelength and same optical power.

Fig. 11. Pump cavity comparison between odd-numbered and even-numbered directions.

Fig. 12. Two VCSEL stacks from a hexagonal pump cavity with three rows of VCSEL arrays each. These two stacks will be combined as an inter-reflective pump chamber.

Fig. 13. Pumping experiments with (a) a water-cooled pump module and (b) a conductively cooled pump module. The 1064 nm output power/energy is measured in a plano–plano resonator with an output coupler with T = 20% (R = 80%) and cavity length of approximately 250 mm.

Fig. 14. Distribution profiles in various cavity setups. The optical efficiency in the profiles above is defined as optical-to-optical efficiency from 808 to 1064 nm. Please notice that (b) and (d) are conductively cooled pump modules without flow tubes, while the rest are water-cooled pump modules.

Fig. 15. (a) Diffusive reflectors made from Spectralon^[27] and (b) material reflectivity^[28]. The reflectivity at 808 nm is approximately 99%.

Fig. 16. Different diffusion solutions in the pump cavity.

Fig. 17. VCSEL pump stack with a frosted flow tube and a Nd:YAG laser rod.

Fig. 18. Distribution comparison between the polished tube and frosted tube in the pump cavity with 5 and 6 mm laser rods.

Fig. 19. Pump power at 808 nm versus 1064 nm output power in a hexagonal pump cavity with a 6 mm Nd:YAG rod and a frosted flow tube^[12].

Fig. 20. MOPA experiment with a 220 mJ seed laser and a VCSEL-pumped amplifier with an 8 mm Nd:YAG rod.

Fig. 21. Centric and eccentric pumping schemes.

Fig. 22. Distribution comparison between centric and eccentric pumping with the same 6 mm laser rod and frosted tube.

Fig. 23. Distribution comparison between centric and eccentric pumping with an 8 mm Nd:YAG rod.