Study On The Influence Of The Quality Factor Of Laser Luminescence On The Measurement Of Laser Damage Threshold

With the wide application of high-power and high-energy laser in industry,national military and even aerospace,optical components are also facing more and more laser damage problems,which are discussed and analyzed by many researchers.Laser damage will affect the working performance of the whole laser optical system.Its threshold is an important index for optical components to resist laser damage.How to accurately measure the laser damage threshold is of great significance to relevant academic research and the development of laser application.A relatively perfect test standard has been formed internationally,namely iso21254 standard,which refers to the method of evaluating and testing laser damage threshold,and has been applied and popularized by many laser technology enterprises.In the definition of international test standard,the laser mode is an ideal TEM₀₀basic transverse mode,and its laser spot energy is Gaussian distribution.In the actual measurement,the mode of high-energy laser is often multimode.If the laser damage threshold is measured and calculated in the ideal laser mode according to the definition of the national standard,the result will have a large error with the result of the laser damage threshold in the actual laser mode.In this paper,the influence of laser mode on damage threshold measurement is studied,and an engineering test model of laser damage threshold based on TEM₁₁mode is proposed.This paper mainly carried out the following work and analysis:1.The relationship between laser damage threshold and beam quality M~2factor is analyzed theoretically.Through theoretical basis,the relationship between laser damage threshold and beam quality M~2factor is obtained,and the numerical simulation model of laser damage threshold and M~2factor is established.The simulation results show that when other conditions are the same,the laser damage threshold will decrease with the increase of beam quality M~2factor.2.The effects of different modes of Hermite Gaussian laser on laser damage threshold are studied.Firstly,the energy distribution expression of Hermite Gaussian laser spot is deduced theoretically,and the energy distribution of laser spot under different laser modes is analyzed by simulation software.The results show that only the laser energy in TEM00 mode is Gaussian distribution,and with the increase of laser transverse mode number,the radius of laser spot is also increasing,and the laser energy distribution becomes dispersed;Secondly,based on the method of laser material interaction,a three-dimensional physical model of the interaction between 1064nm pulsed laser and optical material quartz glass is established.On this model,the interaction between pulsed laser and quartz glass is simulated by using the finite element numerical analysis method,and the transient temperature field under the interaction is obtained.When the surface temperature of quartz glass reaches its melting point,thermal damage occurs.Finally,the laser energy required for thermal damage to quartz glass when the laser modes are TEM₀₀,TEM₀₁,TEM₀₂,TEM₀₃,TEM₁₀,TEM₁₁,TEM₁₂,TEM₁₃,TEM₂₀,TEM₂₁,TEM₂₂,TEM₂₃,TEM₃₀,TEM₃₁,TEM₃₂and TEM₃₃respectively,and the damage thresholds under various laser modes are calculated.The results show that with the increase of laser transverse mode number,the energy required to cause thermal damage to quartz glass decreases,and the laser damage threshold also decreases.3.Based on TEM₁₁laser mode,an engineering test model for damage threshold measurement is established.In the definition of national standard laser damage threshold test,the laser is a Gaussian spot,and the ratio of the energy value of zero damage probability to the area of Gaussian spot is taken as the laser damage threshold.In practical application,the laser spot is not Gaussian distribution.Through the simulation results and theoretical derivation,the engineering test model of damage thresholdF_{th(engineering)}(28)3E/(4?r~2)in TEM₁₁mode is established.In the thermal damage simulation,the damage threshold under TEM₁₁mode obtained from the national standard test model is 23.55J/cm~2,while considering the influence of laser mode on the damage threshold,the damage threshold obtained from the engineering test model is 17.66J/cm~2.4.The laser beam damage threshold of quartz is measured,and the actual laser beam damage factor is calculated.The laser parameters and laser damage threshold test system are built to test the beam quality M~2factor of 1064nm pulsed laser.The results show that the M~2factor in x and y directions isM_x~2=3.98 andM_y~2=4.15.The damage threshold obtained from the national standard test model is 22.31J/cm~2,and the damage threshold obtained from the engineering test model is 16.73J/cm~2.The simulation and experimental results show that due to different laser modes,it will have a great impact on the damage threshold.The engineering test model proposed in this paper can more reasonably measure the laser damage threshold in tem11 mode,which provides a research direction for accurately measuring the laser damage threshold in different laser modes.