Study On All Fiber Laser Multistage Synchronous Pumping MgO:PPLN Picosecond Mid Infrared Laser

As one of the important atmospheric transmission windows,3-5?m mid-infrared laser includes absorption peaks of many atoms and molecules,which is the molecular"fingerprint"region.It has a very important application prospect in the fields of atmospheric environmental monitoring,new medical diagnosis and treatment,infrared photoelectric countermeasures and so on.With the development of laser output mode from traditional long pulse laser(ms,?s,ns)to ultrafast pulse laser(ps,fs),the application research of picosecond 3-5?m mid-infrared laser is further deepened.Using 1?m laser source to pump MgO:PPLN is one of the main techniques to realize continuous tuning output of mid-infrared laser,which the research in this area has important guiding significance for the development of mid-infrared laser.In this thesis,based on the optimization design of Yb-doped all fiber MOPA picosecond laser system and the theoretical analysis and design of synchronously pumped MgO:PPLN OPO and OPA,the high-power picosecond mid infrared laser output of multi-stage synchronously pumped MgO:PPLN OPO and OPA is studied.The primary research work and achievements of the paper is as follows:Theoretically,the pump source Yb-doped all fiber MOPA picosecond laser system and the synchronously pumped MgO:PPLN OPO and OPA picosecond mid infrared laser system are analyzed and designed.In the part of pump source,a novel two-dimensional perovskite material(CH₃NH₃)Pb I₃ is used as saturable absorber to realize mode-locked seed source output of fiber laser.The multistage synchronous delay pulse pumping technology and long period fiber grating negative double cladding tapered gain fiber are used to suppress ASE effect and SRS effect during amplification.In the part of nonlinear frequency conversion,the three-wave coupling model of OPO and OPA in picosecond synchronous pumping system is established and solved.The initial conditions,small signal approximate solution and large signal solution of OPO process are given.The optimal crystal length,linewidth broadening characteristics and wavelength tuning characteristics of OPO and OPA process are analyzed.At the same time,the thermal effect of picosecond synchronously pumped MgO:PPLN crystal is analyzed,a temperature control fixture with side full package is proposed to improve the wavefront distortion.And the folded cavity,bow-tie cavity configuration of synchronously pumped MgO:PPLN OPO and OPA synchronous structure are designed.The results provide theoretical basis and experimental basis for the realization of multi-stage synchronously pumped MgO:PPLN picosecond mid infrared laser output.Experimentally,the high-power picosecond 1064nm fiber laser and multi-stage synchronously pumped MgO:PPLN OPO and OPA were studied.Based on(CH₃NH₃)Pb I₃nano material mode-locked,picosecond all fiber seed laser with the pulse width of 17.4ps,the average power of 10.56m W and the central wavelength of 1063.8nm is realized.By suppressing ASE effect and SRS effect in the process of fiber amplification,the picosecond laser with the pulse width of 17.6ps,the output power of 51.5W,the peak power of 59.88kw and the central wavelength of 1063.8nm is realized.Based on the comparison and optimization of folded cavity and bow-tie cavity as well as the cavity length detuning optimization,the output power of 804m W picosecond 3.8?m idler light is achieved by using fiber laser synchronously pumped MgO:PPLN OPO.The corresponding slope efficiency is12.3%,and the conversion efficiency is 11.49%.The mid infrared tunable laser output of3.6?m?4.1?m under polarization period tuning and 3.6?m?3.8?m under temperature tuning is realized at the same time.Based on this,a two-stage synchronously pumped MgO:PPLN OPA laser system is further studied.In the first stage OPA,the calibration amplification of idler light from 804m W to 2.51W is realized,and the corresponding slope efficiency and the conversion efficiency are 12.11%and 12.19%,respectively.In the second stage OPA,the calibration amplification of idler light from 2.51W to 6.63W is realized,and the slope efficiency and conversion efficiency are 16.40%and 16.46%,respectively.Finally,the idle conversion efficiency of the whole MgO:PPLN mid-infrared laser system is 14.41%.At the same time,it is proved that OPA can effectively restrain the deterioration of beam quality in the process of idle frequency optical power amplification.Finally,the output beam quality is M_X²=2.56 and M_Y²=2.62 by two-stage OPA.Finally,the output of high-power picosecond mid infrared MgO:PPLN laser synchronously pumped by Yb-doped all fiber MOPA laser is realized in this thesis.