Study On Fiber Laser Pumped MgO:APLN Dual Wavelength Mid-infrared Optical Parametric Oscillator

Lasers with wavelengths in the range of 3-5μm have always attracted attention because of their good atmospheric transmittance when acting on the atmosphere.At the same time,dual-wavelength mid-infrared optical parametric oscillators are used in national military,medical,special communications,Air pollutant monitoring and many other fields also play an extremely important role.In view of the shortcomings of the existing dual-wavelength optical parametric oscillators such as complex operation mechanism,difficult gain medium preparation,cumbersome experimental construction process and low overall system stability,this paper uses a fiber laser as the pump source to pump a single gain medium.Adjusting the pump source repetition frequency and the signal light transmittance corresponding to the two cavity mirrors solves the back conversion problem in the process of multi-optical parametric oscillation,and realizes the synchronous output of dual-wavelength parametric light.The specific research contents are as follows:Theoretically,starting from the quasi-phase matching principle and extending to the multiple quasi-phase matching principle,a MgO:APLN crystal that can provide two reciprocal lattice vectors at the same time is designed,which can realize two sets of parametric optical oscillations of 1.57μm,3.3μm and 1.47μm,3.84μm.Theoretical analysis and simulation calculation are carried out for the gain,threshold characteristics,cavity design and mode matching in the external cavity pulse pumped Mult Optical Parametric Oscillator(MOPO).The optimal value range of important parameters such as the ratio of the laser spot to the oscillating parametric spot,and the cavity size.Finally,the energy conversion model of external cavity pulse pumped MOPO is established,and the step-by-step integration method is used to simulate the energy field coupling process in MOPO,and the causes of back conversion in the process of multi-optical parametric oscillation are analyzed.The energy conversion process is regulated to achieve the purpose of inhibiting the reverse conversion.The output characteristics of the pump source of the 1064 nm fiber laser were measured experimentally.The maximum injection power of the pump source was 40.3W,the repetition frequency was selected as 150 k Hz,and the pulse width was 45 ns.According to the theoretical analysis above,the experimental study of the external cavity pulse pump MOPO was carried out..By optimizing the transmittance of 1.47μm and 1.57μm resonant parametric light,the joint output maximum power of 3.3μm and 3.84μm is finally 3.46W;after separating the laser beam,the 3.3μm parametric light power is 1.24 W,and the 3.84μm parametric light power is 2.24 W,and the pulse width is 32.1ns and 34.3ns respectively.At this time,the light-to-light conversion efficiency of the common output is 8.6%,the conversion efficiency of 3.3μm laser is 3.1%,and the conversion efficiency of 3.84μm laser is 5.6%.Theoretical analysis and experimental results are basically consistent.