Study On Thermal Stress Of Fused Silica Damage Induced By Millisecond-nanosecond Combined Pulse Laser

With the development of laser technology,fused silica is widely used in laser systems as an optical material,and its anti-damage ability is widely concerned.A millisecond-nanosecond combined pulse laser irradiation of fused silica can cause a series of complex physical processes such as temperature rise process,thermal stress process,and ignition process.There are many combinations of millisecond pulse laser and nanosecond pulse laser in time.In the process of fused silica damage caused by a millisecond-nanosecond combined pulse laser,different pulse delays will lead to different damage effects of fused silica.Therefore,it is of great significance to analyze the damage process of fused silica induced by a millisecond-nanosecond combined pulse laser.In this paper,theoretical,simulation,and experimental studies are carried out on the temperature rise and thermal stress changes during the irradiation of fused silica by a millisecond-nanosecond combined pulse laser.On the theoretical aspect,based on the heat conduction equation,elastic mechanics theory,and finite element method,the physical process of fused silica irradiated by millisecond-nanosecond combined pulse laser is simulated.In the simulation study,the temperature rise model and stress change model of the interaction between millisecond-nanosecond combined pulse laser and fused silica are established.The thermal stress change of fused silica under different pulse delays and different laser energy densities is studied from the perspective of space and time.During the study of the evolution of temperature with time,the physical process of latent heat of phase change is simulated,and the distribution characteristics of temperature on the surface and the inside of fused silica are analyzed,respectively.At the same time,the variation laws of radial stress,circumferential stress,and axial stress of fused silica irradiated by millisecond-nanosecond combined pulse laser are analyzed.On the experimental aspect,the change process of temperature rise at the center of the upper surface of fused silica irradiated by millisecond-nanosecond combined pulse laser with different pulse delay and different laser energy densities is measured and analyzed.The real-time temperature monitoring results are consistent with the simulation temperature calculation results.By collecting the experimental data of temperature changing with time,the variation law of peak temperature with pulse delay and laser energy density is found.The stress of fused silica irradiated by millisecond-nanosecond combined pulse laser is measured by a polarizing stress meter,and the effects of pulse delay and laser energy density on the stress of fused silica in millisecond-nanosecond combined pulse laser are discussed.The damage morphology of fused silica is obtained by a metallographic microscope,and the thermal stress spalling phenomenon is found near the laser irradiation boundary on the front surface of fused silica.The growth law of damage area on the front surface of fused silica is discussed,and the threshold of fused silica damage induced by millisecond-nanosecond combined pulse laser is obtained.Finally,combined with the simulation results and experimental results,the thermal stress damage mechanism of fused silica irradiated by millisecond-nanosecond combined pulse laser is expounded.