A 1.9μm Tm: YLF external cavity mode conversion vortex laser based on LD off-axis pump

In this work, a 1.9μm Tm:YLF high-order vortex laser output is realized for the first time based on LD off-axis pumping technology. By adjusting the off-axis displacement of the output coupling mirror accurately, the maximum topological charge up to m=20 for stable Hermite–Gaussian (HGm,0) mode is achieved. The conversion of high-order HGm,0 to Laguerre–Gauss (LGm,0) modes are further realized by a π/2 mode converter, and the topological charge and chirality of LGm,0 modes are measured by the Mach–Zehnder (MZ) interferometer system. The maximum output power of the LG1,0 mode vortex laser was measured to be 8.5W with the central wavelength of 1908.8 nm. The wavelength and the power instability are less than 0.72 nm and better than ± 5.9%, respectively. This work proves that the 1.9μm Tm:YLF laser has the potential to achieve continuous tuning and easy chirality control for the high-order vortex optical mode output, and lays a foundation for high-power mid-infrared vortex laser applications.