Fig. 1. Application of visible vortex laser in high resolution imaging and underwater communication

Fig. 2. Laser source that directly generates vortex beam. (a) Frequency doubled laser generating vortex laser based on thermal lens effect^[37]; (b)-(c) Nd:GdVO₄ intra-cavity frequency doubling laser based on point defect mirror technology^[38-39]; (d) Nd:YVO₄ intra-cavity frequency doubling laser based on hemispherical resonator^[40]

Fig. 3. An experimental device for output visible vortex beam based on an external cavity helical phase plate modulation element combined with frequency doubling. (a) Vortex green laser based on LBO frequency doubled crystal^[46]; (b) Visible vortex Raman laser based on Ba(NO₃)₂ Raman crystal^[49]

Fig. 4. Typical device diagram of visible vortex beam based on external cylindrical lens mode converter combined with frequency doubling output^[54]

Fig. 5. Direct-pumped visible solid-state vortex laser generation methods

Fig. 6. Two ways to realize off-axis pumping technology

Fig. 7. Visible vortex laser generation based on off-axis pumping technology. (a) Chiral controllable vortex laser with off-axis pumping structure^[61]; (b) Intracavity frequency doubling Pr:YLF laser and ultraviolet high order structured light field based on off-axis pumping structure^[61]; (c) Off-axis frequency doubling Pr:YLF vortex lattice laser^[63]

Fig. 8. Wavelength-tunable vortex laser at 604 nm and 607 nm based on off-axis pumping technology of crystal rotation^[69]

Fig. 9. Q-switched vortex laser device based on annular pumping technology^[78]

Fig. 10. Schematic diagram of enhanced spherical aberration selection mode

Fig. 11. Vortex laser device based on spherical aberration mode selective. (a) 640 nm visible vortex laser^[80]; (b) 607 & 640 nm wavelength-switchable vortex laser ^[81]

Fig. 12. Schematic diagram of vortex generation method in fiber laser

Fig. 13. Fiber vortex laser based on the core-shifted fiber coupling method. (a) Schematic of the visible all-fiber laser and the principle of core-shifted fiber coupling method^[86]; (b) Red-green pulse vortex fiber laser^[82]

Fig. 14. Vortex fiber lasers based on specially designed mode selectors. (a) Wavelength tunable visible vortex fiber laser^[83]; (b) All-fiber passive mode-locked vortex laser at 634.4 nm^[87]

Fig. 15. Ultra-compact vortex laser based on Pr:WPFGF single crystal fiber. (a) Schematic of laser experimental setup; (b) Schematic diagram of wavelength selection method ^[88]