Research On The Key Technologies Of Thermal And Electrical Control In Mid-Infrared All-Solid-State Laser

Since 3~5?m mid-infrared laser has minimum attenuation in atmospheric transmission and covers the absorption peaks of many atoms and molecules,it is widely used in laser spectroscopy,atmosphere monitoring,electro-optical confrontation,laser remote detection and other related fields.To further promote the stability,reliability and environmental suitability of the mid-infrared laser,and satisfying the harsh requirements on scale,weight and power dissipation of laser in complex environments such as airborne and space,the developed all-fiber-laser pumped MgO:PPLN mid-infrared solid-state laser was taken as an example in this thesis,focusing on the high stability and high precision temperature control of the seed source,laser medium,non-linear optic crystal and other key optical devices in the laser,high stability drive and non-liquid heat dissipation of high power pump laser,and other electric and thermal key technology issues.The model identification and control technology of thermoelectric cooling system,the constant current driving technology of semiconductor pump laser and the non-liquid thermal control technology of mid-infrared all-solid-state laser were researched separately.The main research work of this thesis is as below:1.For the thermoelectric cooling temperature control system which made up of semiconductor thermoelectric cooler,simulated thermal load and radiator,the thermodynamic equilibrium equations of the temperature control system were established based on the semiconductor thermoelectric effect principle.The mathematical model of the temperature control system was confirmed by using small signal linearization method on the equations,and the dynamic model has single zero,two poles and delay characteristics.The system model parameters identification experimental platform was established and a five-order pseudorandom binary M length sequence was designed as the input signal of system identification.The least-square algorithm was used to identify the model parameters of the temperature control system,and the model parameters under different thermal loads and excitation signals were achieved.The model parameters were shown to vary with different operating conditions.For the non-linear and time-varying characteristics of the temperature control system,a parameter self-tuning fuzzy PID(Proportion-Integral-Differential)controller whichbased on fuzzy control and PID control was designed,the PID parameters are set online by fuzzy inference,and the system temperature control effect of different control methods were compared and analyzed through Simulink in Matlab.2.The basic operating principle,output characteristic,the influence of temperature change on threshold current,output power and wavelength,device failure mechanism of the semiconductor were analyzed deeply.Based on the principle of the depth negative feedback constant current driving circuit,a digital dual-closed-loop mode LD(Laser Diode)constant current driving method was proposed,which using outer ring control based on the depth negative feedback amplification circuit and PID inner ring control.A input power filter circuit was designed and used to denoising the power supply.The stability and accuracy of the driving circuit output current was enhanced effectively.Combing the main causes of the semiconductor laser failure,the current limiting protection circuit,the soft-start protection circuit based on digital delay control and the surge protection circuit were designed for the LD driving circuit,which increased the safety and reliability of the semiconductor laser.3.A miniaturized non-liquid cooling thermal control system which made up of thermoelectric cooler,automatic temperature control circuit,cooling fins,axial fans and heat pipes was designed for the all-fiber-laser pumped MgO:PPLN mid-infrared all-solid-state laser.A mathematical model and method was established to estimate the heat dissipation capability of the non-liquid cooling thermal control system of laser under different ambient temperatures approximately.A finite element model of the laser heat dissipation system was established in the COMSOL simulation software.The steady-state heat distribution of the system was simulated in the software,and the influence of the heat pipe and the speed of the fan on the heat dissipation system were analyzed contrastively.The maxim heat dissipation capability of the laser thermal control system was estimated approximately based on the simulation results and mathematical model.The laser light emission experiments were conducted under room and high temperature environments separately,the temperature of pump laser source could be controlled within ± 0.1°C steady-state error in the laser working process.The theoretical simulation and experimental results show that this non-liquid cooling thermal control scheme improved the environment adaptability of this mid-infrared all-solid-state laser effectively,this scheme is also available for the heat dissipation of solid-state laser with hundreds of watts pump power.