3.5?m Q-switched And Mode-locked Er³⁺-doped ZBLAN Fiber Laser Based On Dual-wavelength Pumping

The application of mid-infrared lasers in various emerging science and technology and basic research has received extensive attention in academic,medical,national defense,and industrial fields.To meet the application needs of various occasions,it is necessary to develop a practical mid-infrared fiber laser with high power,high efficiency,wide tuning range,high beam quality,ultra-short pulse width,high peak power,and stable output.This thesis mainly focuses on the challenges faced in the research process of 3.5?m Er³⁺-doped ZBLAN continuous-wave(CW)and pulsed fiber lasers.CW lasers are explored with the improved pumping schemes,while pulsed lasers are explored with passive Q-switched and NPR techniques.Then a series of theoretical and experimental studies are carried out.The main work includes:1.Based on the energy level transition process of Er³⁺ions,a theoretical model of a3.5?m fiber laser with the improved pumping scheme at 655 nm and 1981 nm is established.Secondly,the numerical simulation and parameter optimization of the laser system is carried out using the model.Finally,on the theoretical basis,a corresponding experimental system is built to achieve a 3.5?m laser output of 1.72 W,where the slope efficiency with respect to the launched 1981 nm pump is 31.5%.Direct comparison with the cascaded pumping scheme is performed.Under the same 1981 nm pumping power,the improved pumping scheme can obtain higher output power and lower lasing threshold,and the accuracy of the theoretical model is verified.2.Based on a reflective Fe²⁺:ZnSe crystal,the 3.5?m Er³⁺-doped ZBLAN passively Q-switched fiber laser is built,and a stable pulse with an average power of 267.8 mW is achieved with an energy of 5.25?J.Secondly,the 3.5?m Er³⁺-doped ZBLAN fiber laser based on polarization-maintaining fiber is studied.The system can obtain a continuous laser output of 307 mW.At the same time,by rotating the grating,the stable continuous polarization light can be continuously tuned in the range of 3449?3548 nm.The internal energy is too low so the Fe²⁺:ZnSe mirror cannot achieve the effect of saturable absorption,resulting in no pulse output.Finally,optimization measures are proposed.3.Based on the coupled Ginzburg-Landau equation and the working principle of NPR technology,the theoretical model of a 3.5?m Er³⁺-doped ZBLAN mode-locked fiber laser is established by using the pulse tracking method.And the fractional-step Fourier algorithm is used to study the effects of gain saturation energy and wave plate phase delay on pulse output characteristics.Then the system structure parameters are optimized.Secondly,the corresponding laser is built which can emit a maximum power of 170 mW in the annular cavity,and the reasons for the low output are analyzed.After adding an isolator and two wave plates,the laser output is not realized due to the low energy in the cavity,the large loss of the NPR structure,and the limited power of the pump source.Finally,the corresponding solution is given,and the validity of the model is verified by comparison with the experimental results of others.