2-5 μM Widely Tunable MgO:PPLN Optical Parametric Oscillator

Mid-infrared(MIR)lasers emitting around 2-5 μm wavelength band exhibit great application requirements and irreplaceable value in the fields including gas monitoring/detection,national defense and military,medical diagnosis,polymer processing,precision spectroscopy and frontier science,etc.It has always been the focus of attention of laser technology researchers at home and abroad.Compared with other techniques,due to the merits of high power,high efficiency,wide tunable range,low power consumption,small volume and weight,easy integration,optical super-lattice based optical parametric oscillator(OPO)has proved to be the most commonly used technique to obtain widely tunable 2-5 μm laser output.This thesis is focused on the study of miniatured,widely tunable 2-5 μm optical superlattice based OPO,makes breakthroughs in the key technologies such as wide band tuning,linewidth and beam quality control,intra-cavity OPO cavity design,realizes widely tunable 25 μm MIR laser emitting in continuous wave(CW),narrow linewidth CW and nanosecond operation mode.The developed tunable narrow linewidth 2-5 μm MIR PPLN-OPO can realize the replacement of high-end laser products by domestic production,which has important economic significance and social value.The details are as following:Chapter 1:It introduces the important applications of 2-5 μm MIR laser in various fields,analyzes the realization methods of 2-5 μm MIR lasers and the important progress of optical superlattice OPO at home and abroad,and briefly describes the main research contents of this thesis.Chapter 2:The OPO principle is described.The nonlinear coupled wave equation,the threshold condition and characteristics of conversion efficiency of OPO are analyzed.Then the birefringence phase matching and quasi-phase matching technologies are introduced in detail.This chapter provides a theoretical basis for the experimental research of this thesis.Chapter 3:Experimental study of nanosecond wide tunable MIR OPO.(1)By using a 1.06μm nanosecond fiber laser to pump a muti-period(29-31.6 μm)MgO-doped periodic poled lithium niobate(MgO:PPLN)crystal,combining period and temperature tuning,the continuously tuned 2.37-4.01 μm MIR laser output is realized.When the pump power is 9.95 W,the average output power is greater than 1.7 W in 2.37-3.75 μm range.The results provide experimental basis for the research and development of miniaturized widely tunable MIR laser source.(2)The laser performance of 2.1μm laser pumped phosphor zinc germanium(ZGP)OPO MIR laser is studied.The maximum output power of 4.3 μm laser is 10.62 W.By comparation with the 4.3 μm PPLN-OPO,the potential of optical superlattice OPO in high power 4.3 μm MIR laser generation is evaluated.Chapter 4:Experimental study of CW wide tunable MIR OPO.(1)Two multiperiod MgO:PPLN crystals were pumped by a narrow linewidth single-frequency fiber laser.Coordinating crystal period tuning,temperature tuning,etalon tuning,PZT tuning methods,narrow linewidth wide tunable 2.2-5.1 μm MIR laser operation is realized.The corresponding output power is>520 mW@2.2-4.0 pm,>60 mW@4.0-4.3 μm,≥15 mW@4.3-5.1 μm.The typical spectral line width is<1 MHz,and the RMS of 8-hour output power stability at 2.7 μm was 1.43%.It is in an advanced position in narrow linewidth continuous tunable lasers.The engineering design,the index of Germany Toptica product,with import substitution ability.(2)A tunable MIR laser output of 2.7-4.1 μm continuous wave is obtained by using the intra-cavity OPO structure,where a Nd:YVO4 crystal is applied as the laser crystal.Fixed the pump power at 14.8 W(Limited by the coating parameters of the cavity mirror,the pump power is increased to 19 W in 2.73-2.83 μm),the output power of is determined to be>20 mW@2.7-3.0 pm,>100 mW@3.0-4.0 μn,>50 mW@4.0-4.1 μm.The beam quality factor M2 at 3.4 μm is 1.89.The RMS of 6-hour output power stability at 3.2 μm is measured to be 3.83%.The miniaturized,low-power consumption,2.7-4.1 μm widely tunable MIR laser has an important application prospect and has been successfully verified in the response of MIR detector.Chapter 5:The research work of this thesis is summarized,and the development prospect of 2-5 μm wide-tuned optical superlattice-based MIR OPO is presented.It is pointed out that high quality optical superlattice crystal is the key to realize high-power,widely tunable 2-5μm MIR laser.Miniaturization,low power consumption,lightweight,and integration are the inevitable trend of the development of optical superlattices based MIR OPO.