Research development on Tm³⁺/ Ho³⁺ ions doped mid-infrared ultrafast lasers (Invited)

Due to the wide applications, rare earth ions Tm³⁺/ Ho³⁺ doped mid-infrared 2 μm ultrafast laser has become one of the hot research topics in the laser field in the past decade. In this paper, the development progress of mode-locking techniques at 2 μm was firstly reviewed, including active mode-locking techniques and passive mode-locking techniques based on the effects of saturation absorption, Kerr lens, nonlinear polarization rotation, nonlinear optical loop mirror, nonlinear multimode interference. Secondly, the development on Tm³⁺/ Ho³⁺ doped solid and fiber mode-locked laser pulse compressions was reviewed from the sides of the laser gain media and dispersion management techniques. Thirdly, the technical routes of realizing Tm³⁺/ Ho³⁺ high-power and high-energy ultrafast lasers were summarized. Finally, the development trends for 2 μm ultrafast lasers were concluded and outlooked.