Research On MgO:PPLN Mid-Infrared Optical Parametric Oscillator Pumped By 1064nm Ytterbium-doped Fiber Laser

3～5μm is located in the atmospheric window band,which shows important application value and far-reaching development significance in military and civilian fields,such as military countermeasure,spectral analysis,remote sensing,communication,environmental monitoring and so on.It makes the mid-infrared laser become the key research project of each research group.The quasi-phase-matched optical parametric oscillator(QPM-OPO)based on nonlinear optical frequency conversion technology has wide tuning range,high conversion efficiency,flexible tuning mode and simple and compact structure.This technical method can effectively generate coherent beams in the mid-infrared band.There is a serious thermal effect problem and complex overall structure in traditional all-solid-state OPO.Moreover,it is difficult to take into account high repetition rate and high peak power at the same time.In order to solve the above problems,using 1064 nm Yb3+-doped fiber laser(YDFL)as pump source,based on quasi-phase matching optical parametric oscillation theory and super-threshold multiple model,the structure design and output characteristics of mid-infrared MgO:PPLN-OPO are studied systematically,and a 3.8μm laser with high power and high conversion efficiency is obtained.In theory: Firstly,based on the three-wave coupling equation,the principles of QPM technology and optical parametric oscillation technology are briefly expounded.Furthermore,the tuning curve of nonlinear gain medium MgO:PPLN is calculated.After that,the threshold characteristic of MgO:PPLN-OPO is analyzed,the super-threshold multiple model is established.Moreover,the changing trends of OPO gain,threshold,linewidth and their influencing factors are calculated theoretically.Furthermore,the effects of peak power,linewidth and polarization extinction ratio of 1064 nm fundamental light on OPO are summarized,and the requirements for 1064 nm YDFL pump source are put forward.on the basis of which the optical parametric oscillator is optimized and the specific parameters of the resonator are determined.In experiment: Firstly,using 1064 nm YDFL as the excitation source of this experiment,the output characteristics of ordinary and narrow linewidth fiber laser are tested,and the excellent characteristics of 1064 nm pump source are determined.After that,the experimental study on MgO:PPLN-OPO pumped by 1064 nm YDFL is carried out,and the threshold,output power and conversion efficiency of parametric laser under different pump peak power,different pump pulse duration and different pump linewidth are compared.Finally,when the pump power is 40 W,duty cycle 0.4%,pulse width 100 ns,linewidth 2.5nm,the maximum power of 3.8 μ m parametric light is 3.6W,the pulse width is 56 ns,the corresponding optical-to-optical conversion efficiency is 9%,and the beam quality M2 is 2.34.