Research On The Evaluation Method Of Damage Efficiency Of Laser-induced Optical Thin Films

With the development of modern laser technology,laser weapons have gradually entered actual combat.As an important component of the information perception system,the optical film becomes the key factor that makes the power of opponent have huge loss.The damage efficiency of high-energy lasers to optical thin films has also got high attention.Due to the instantaneity of laser damage and the high cost of test equipment,the evaluation is difficult to proceed.The damage effect of thin film materials can be effectively studied and analyzed by numerical simulation.Due to the irradiation characteristics of laser weapons and the particularity of the structure and function of optical films,this paper adopts the target Vulnerability/Lethality assessment method based on virtual model.In the atmospheric environment,the influence of different laser parameters on the damage effect of thin film materials is obtained by using the change of laser parameters.The research on target vulnerability is mainly based on the thermal damage mechanism of thin film materials.From the heat transfer theory,the damage state of the thin film material is obtained through the physical field coupling between the laser and the material.The main work and results of the paper are as follows:1)By analyzing the damage mechanism of laser to thin film materials,focusing on the Al2O3 thin film as the main research object,it is concluded that the main damage mechanism of optical thin film under laser irradiation is thermal damage.Due to the influence of thermal effect,the temperature change is determined as the evaluation criterion for laser damage to optical films.2)Establishment of a thermal-force field model for the interaction between single-pulse laser and thin-film materials.Using the finite element method to simulate the model,which obtained the temperature field and thermal stress field distribution of the laser acting on the optical thin film material.Through the research and analysis of the simulation results,the results show that when other conditions unchanged,the temperature and thermal stress of the optical film increase with the increase of the laser energy,and decrease with the increase of the spot radius.The greater the laser energy,the smaller the spot area,the more vulnerable the optical film is to damage,and the deeper the damage.3)Establishment of thermal elastic-plastic calculation model and melting model.When the laser energy is 20J and the spot radius is 4mm,the thermal elastoplastic transformation state and melting state of the Al₂O₃ film are subjected to finite element simulation analysis.It is clear that when the optical film material enters the plastic state,damage begins to occur;when the temperature reaches the melting point,it enters a state of complete damage.By calculation,the Al₂O₃ film enters the plastic transition at 0.065ms,at this time,the maximum temperature of the irradiation center is 381.61K.At the completion of one pulse,complete damage is not achieved,and the maximum temperature of the irradiation center is 1283.02K.4)Integrating laser and material damage data.It is concluded that when the temperature is396K～2045K,the damage state of the Al₂O₃ film is in the general damage state;when the temperature is greater than or equal to 2045K,the Al₂O₃ film is in a state of complete damage.The damage state of the Al₂O₃ film is verified when the laser parameters are changed.Through comprehensive analysis,under a single pulse,when the laser energy is less than 2.5J,the optical film appears without damage;when the laser energy is less than 33.08J,the optical film is not completely damaged.The research in this paper accomplishes the accurate evaluation of the damage effect of optical thin films under laser irradiation.At the same time,it provides an important reference for the laser to precisely strike the target,optimize the coating process,prepare the film with strong laser resistance,and extend the use of the optical system.