Research On Pumping Characteristics Of Mid-infrared Optical Parametric Oscillator Based On MgO:PPLN

With the rapid development of optoelectronic information technology,the infrared light source in 3~5?m has important application prospect in the field of spectroscopy,remote sensing,laser communication and so on,it is very important to carry out the research of this laser band.The research shows that the mid-infrared laser output based on optical parametric oscillator has the merits of small size,light weight,stable performance,good reliability and high beam quality,and have the advantages of wide spectral range.In view of this,relying on the laboratory infrared laser project,this topic will carry out the study of the infrared optical parametric oscillator.In this paper,we will use fiber lasers as pump source to study the mid-infrared optical parametric oscillator based on Mg O:PPLN crystal,and the main target is research on how to obtain a more efficient and stable mid-infrared laser prototype by reasonable optical design.The work contents are as follows:(1)Investigating the common implementation of the mid-infrared laser and the current research situation at home and abroad,based on which establish the way of OPO to achieve the output of infrared laser.The theoretical basis of nonlinear optical parametric oscillator is set up,and the different optical resonators are compared with each other and the optical system structure of OPO is designed and simulated by Code V.(2)Based on the OPO mathematical model of the relationship between the focusing parameter and the threshold of OPO,the connection between the focusing parameter and the parameter conversion efficiency is simulated and analyzed,and the optimal focusing parameter under ideal condition is obtained.On the basis of the analysis,the applicable range and limitations of the conclusions are analyzed.The thermal effect of crystal under high pump power and heating is analyzed by establishing heat conduction equation.It is pointed out that the over-focusing of pump light will lead to the thermal lens effect inside the crystal be enhanced.The temperature distributions of the crystals were analyzed under different pump powers and different focusing parameters.(3)Through the software of Code V,the beam-focusing system is designed and simulated,the simulation results can be used to guide the tuning of the pump spot focusing parameters.Based on Mg O:PPLN crystal and fiber laser,the experimental structure of OPO was built.The effect of focusing parameters on OPO is studied by using Mg O:PPLN crystal.The experimental results show that the parameters of the spot focusing can achieve higher parameter conversion efficiency under lower input pump powers.However,when the pump light increases,the optimal focusing parameter decreases gradually.The higher the pumping power is,the smaller the optimum focusing parameter is.(4)The effect of spot matching on the wavelength tuning is studied experimentally.The experimental results show that the larger the focusing parameter is,the larger the internal temperature gradient is,so it has some influence on the wavelength tuning.In order to obtain a stable wavelength output,a smaller focusing parameter should be chosen to reduce the influence of the focusing parameters on the wavelength tuning under high pump power conditions,which also leads to higher conversion efficiency.(5)On the basis of the linear cavity,the V-cavity OPO experimental structure is set up.The experimental results show that the V-shaped parametric light output is not collinear with the pump light,which can avoid the coupling effect.However,the laser threshold is higher than that of the linear cavity,and the optical-to-optical conversion efficiency drops significantly,which is not good for realizing the high efficiency operation of OPO system.