【摘要】 基于自主研制的72冲程薄片泵浦模块，研制出百瓦级Ho∶YAG薄片激光器，连续波激光输出功率超150 W，光-光转换效率为44.18%，斜效率为48.29%,x方向和y方向的光束质量因子分别为2.64和2.42，波长为2090 nm和2097 nm。更多还原

【Abstract】 Objective High-power lasers operating in the 2μm region have been used extensively in scientific research,national defense,laser medicine,and environmental monitoring.Currently,2μm lasers are primarily generated via two technological approaches.One method involves the indirect generation of 2μm laser through optical parametric oscillation （OPO）.However,this method is associated with complex systems and inferior beam quality,thus rendering it difficult to achieve a fundamental-mode output.By contrast,the other approach involves an oscillator emitting a 2μm region directly based on a gain medium doped with Ho3+.Owing to its simplicity and efficiency,researchers are focusing on its potential application.In thin-disk lasers （TDLs）,the thickness of the gain medium is only a few hundred micrometers.Compared with fiber lasers,TDLs allow for a larger radial-longitudinal ratio and have fewer nonlinear effects.Additionally,compared with rod lasers,the large diameter-to-thickness ratio of the Ho∶YAG thin disk ensures an almost one-dimensional heat flow through the disk,thus minimizing thermal effects.In recent years,researchers worldwide have focused on multipass-pumped Ho∶YAG TDLs.In 2021,Tomilov et al.achieved an output power of 112 W with an optical-to-optical efficiency of 54.6%using a 72-pass pump module.Owing to constraints in key technologies such as multipass module design,ultrathin crystal processing,and heat-removal design,studies regarding 2μm TDLs can not be conducted in China.Methods We construct a Ho∶YAG TDL using our custom-developed 72-pass module （Fig.5）.First,we analyze the energy levels and fluorescence spectrum of the Ho∶YAG laser.Subsequently,based on the absorption-efficiency curve of the crystal for the pump,we select a Ho∶YAG thin disk,which enables the reflectivity of the crystal to reach 99.98%,with a surface figure of 0.072λ（λ=632.8 nm）.Subsequently,a V-shaped cavity is constructed,and the pump spot is rescaled for a high-power continuous wave （CW）output.Finally,the beam quality factor is obtained using the knife-edge method and the laser spectrum is analyzed using an infrared spectrometer.Results and Discussions Based on a pump spot diameter of 3.6 mm,the output power and optical-to-optical efficiency curves as a function of the pump power at different output coupling ratios are shown in Fig.10.When the pump power is 300 W and the output coupling ratio is 3%,the output power is 129.8 W,the optical-to-optical efficiency is 43.27%,the slope efficiency is 46.98%,and the corresponding pump power density is 2.9 kW/cm².Figure 11 shows the curves of the output power and optical-to-optical efficiency versus the pump power based on a pump beam diameter of 4.5 mm.The results indicate that a maximum output power of 150.2 W is achieved through beam-spot scaling,which corresponds to a pump power density of 2.0 kW/cm²,and no saturation effects.The optical-to-optical efficiency is 44.18%,which is comparable to that obtained under D_pump=3.6 mm （corresponding to a pump power density of 2.9 kW/cm²）,and the slope efficiency is 48.29%.However,because of the limitations of the pump source,the output power cannot be further increased.By fitting the beam-propagation equation to the data shown in Fig.12,the beam quality factors are measured to be 2.64 and 2.42 in the x-and y-directions,respectively,using the 90/10 knife-edge method.Figure 13 shows that the output spectrum of the Ho∶YAG TDL exhibits two peaks at 2091 nm and 2097 nm.Subsequently,wavelength selection will be performed using a Fabry-Perot （F-P） etalon.Conclusions In this study,a custom-developed 72-pass pump module pumped with a Tm-doped fiber laser at 1908 nm is utilized.A 186-μm-thick Ho∶YAG thin disk with a doping mass fraction of 2.5%and a diameter of 10 mm is used.By integrating certain coating techniques,an absorption efficiency of 97.09%is achieved.The surface figure of the Ho∶YAG thin-disk crystal with a diamond heat sink is 0.072λ.In conclusion,a maximum output power of 150.2 W,a slope efficiency of 48.29%,and an optical-to-optical efficiency of 44.18%are achieved.The beam quality factors are 2.64 and 2.42 in the x-and y-directions,respectively.To the best of our knowledge,this is the highest CW power achieved using a Ho∶YAG TDL reported thus far.By increasing the pump power and scaling the pump spot size,a higher output power can be achieved.This study establishes a crucial technological foundation for the development of 2.09μm pulsed lasers with high average-power levels.更多还原