Designable multi-wavelength operation at 2.1 µm from a composite holmium-doped gain medium intra-cavity pumped by a thulium laser.

Owing to the narrow-bandwidth and multi-peak emission spectrum characteristic of holmium-doped laser media, the wavelength expansion potential of 2.1 µm holmium lasers is inherently limited. This paper proposes what we feel is a novel design scheme based on a composite holmium-doped medium intra-cavity pumped by a thulium laser. A 785 nm LD-pumped Tm:YAP laser was constructed as the intra-cavity pump source, while Ho:YAP crystal and Ho:Y2O3 ceramic were co-placed within the resonator as synergistic gain units, forming an equivalent composite Ho:YAP/Y2O3 gain medium. Simultaneous three-wavelength operation at 2102 nm, 2117 nm, and 2129 nm is successfully demonstrated, achieving a maximum output power of 2.02 W with a slope efficiency of 14% with regard to the 785 nm pumping. The composite gain medium scheme eliminates the dependency on complex design and fabrication process of as-grown holmium-doped materials, offering advantages such as simplified design, high controllability, and excellent scalability. This work provides a feasible pathway for the design and configuration of designable multi-wavelength laser sources in the 2.1 µm band.