Research On Optical-Mechanical-Thermal Coupling Analysis Technology Of Laser System Facing Complex Environment

The 3-5?m medium-wave infrared laser and the 9-11?m long-wave infrared laser locate in the atmospheric transmission window,the laser energy of both laser slightly attenuate during the transmission process,and high average power and pulse peak power can be output at the same time.This makes it widely used in many industrial and national defense fields such as atmospheric environment monitoring,photoelectric countermeasures,high-precision laser manufacturing,lidar,and photoelectric detection.In order to improve the reliability,stability and adaptability of the laser to the environment,and at the same time to meet the strict requirements of the weight,volume,power consumption and operating temperature of the laser in the complex airborne environment,this thesis is based on the optical-mechanical-thermal coupling design method.Taking the airborne atmospheric monitoring CO₂ laser as an example,the optical-mechanical-thermal coupling analysis of CO₂ laser system was carried out.At the same time,according to the opto-mechanical characteristics of optical components in mid-infrared solid-state lasers,research on high-precision temperature control technology for key components of lasers is carried out.Firstly,combined with the optical and structural characteristics of the laser,the basic principle and finite element simulation method of the opto-mechanical thermal coupling analysis method with heat transfer as the node are analyzed.In terms of theory,the applicability of typical heat transfer methods is analyzed according to the operating conditions of airborne lasers,and the working principles of small and light temperature control elements such as thermoelectric refrigeration(TEC)and heat pipes are introduced in detail.In terms of simulation analysis,the finite element method of temperature field analysis and thermoelastic analysis is introduced.The research in this chapter provides theoretical and simulation support for the subsequent design of the laser system and the temperature control scheme of key components.Then,the optical-mechanical-thermal coupling analysis of CO₂laser system under airborne conditions was carried out.According to the working requirements of airborne environmental lasers,combined with the optical-mechanical structure and working characteristics of CO₂ lasers,a closed-loop laser temperature control scheme based on laser working performance-TEC temperature control capability-ambient temperature-heat dissipation structure is established.And establish a finite element analysis model including laser thermal-structure-flow field.The solution has wide temperature adjustment capability:under high temperature conditions,the laser is cooled by the TEC cold end,and the TEC hot end is dissipated by forced air cooling.According to the normal working characteristics of the TEC,parameters such as fans and fins are optimized based on the finite element analysis model;under low temperature conditions,change the input direction of the TEC current to heat the laser to form a thermal balance between the environment,the laser and the TEC,and simulate the calculation of the heating process of the laser temperature change.According to the temperature field distribution of the laser after active temperature control is applied in the high and low temperature environment,the deformation of the front and rear window mirrors of the laser resonator caused by the temperature change is simulated and calculated.Build a CO₂ laser high and low temperature experimental platform,set the temperature variable according to the airborne use requirements,install a temperature sensor to collect the temperature change of the laser during the experiment.Compare and test the laser output power under high and low temperature conditions with the laser output power under laboratory room temperature conditions.The effectiveness of the temperature control scheme is verified by experiments.Finally,the research on temperature control technology of key optical components in mid-infrared solid-state lasers is carried out.Different from CO₂ lasers,the optical components in solid-state lasers are more sensitive to temperature,and require higher temperature control accuracy.Therefore,according to the opto-mechanical characteristics of the isolator,a temperature control scheme consisting of axial fans,cooling fins,TECs and heat pipes is established;according to the working mode and temperature requirements of MgO:PPLN optical crystal,a crystal heat sink structure including passive thermal insulation layer and active TEC temperature control crystalline is designed.As the key to precise temperature control of optical components,performance of TEC directly affects the temperature control effect.Based on the finite element method,the TEC electrothermal conversion process was established,and the TEC simulation parameters were transferred to the temperature control simulation model of the isolator and MgO:PPLN crystal,and the steady-state temperature distribution of the isolator and the crystal was calculated.The results show that the temperature control requirements of the key components of the mid-infrared solid-state laser are met.