Cryogenic Cooling in Co-doped Laser Systems: Challenges and Limitations

However, the up-conversion mechanisms of both doped ions can be detrimental as they produce excessive heat, which presents challenges for effective heat management. Cryogenic cooling is typically employed in co-doped laser systems to mitigate up-conversion for optimal laser performance. In 2013, Li et al. demonstrated the effectiveness of a cryogenically cooled, double-end pumped b-cut Tm,Ho:YAP laser, which achieved a continuous-wave (cw) output power of 15 W at 2.12 μm, with a beam quality factor M2 of 1.3[1]. Subsequently, they utilized two Tm,Ho:GdVO4 crystals under identical cooling conditions and successfully delivered a cw output power of 20.5 W at 2.05 μm, while maintaining an M2<1.2[2]. Li Gang reported a 23.4 W Tm,Ho:YVO4 laser cooled with liquid nitrogen in 2013, with an M2 of 1.85[3]. In 2017, Sato et al. employed a side-pumped laser head for Tm,Ho:YLF crystal and achieved an average output power of 7.28 W at a cooling temperature of -80 ℃, with an M2<1.5. However, cryogenically cooled laser systems are complex and bulky, which limits their applicability in various fields. Additionally, the crystals and optical elements used in these systems are susceptible to fracture and surface damage, making them unsuitable for long-term operation.