Study On Damage Characteristics Of Molten Silica With Laser-induced Defective Structures

As a highly reliable transparent material,molten quartz is widely used in large-scale laser optical systems.However,the damage resistance of the components themselves and the limitations of modern component preparation processes jointly hinder the development of laser systems to higher energy,which has also become one of the important directions to be overcome.Amorphous Si O₂,the most commonly used component in modern optical systems,is subject to optical damage in high-energy laser systems,and this optical damage is the most important factor in reducing the beam quality and loading capacity of optical systems.Due to the limitation of the preparation process,bubble impurity defects and multi-bubble coupling defects are generated inside the fused quartz element,resulting in a decrease in the fused quartz damage threshold,thereby reducing the life of the overall system.Therefore,it is very important and practical to carry out the study of temperature rise change,stress-strain process,light field modulation phenomenon,and surface combustion wave formation and expansion process during the interaction between millisecond laser and fused quartz material.In terms of theoretical research,combined with heat conduction equation,elastic equation,Mie scattering theory,fluid mechanics theory and other related theories,the research status at home and abroad is analyzed,and the process of damage of molten quartz elements containing bubble-type impurity defects during laser irradiation is analyzed from a theoretical point of view.By establishing the expression of heat conduction equation with multiple heat sources,the model of the modulation effect of impurities on the laser light field inside the molten quartz,as well as the temperature rise,stress-strain model and combustion wave generation and expansion model of the material after laser irradiation are obtained.In terms of simulation research,based on theoretical research and using finite element analysis method,a damage model of fused quartz containing impurities and defects under laser irradiation is established,and the damage law of fused quartz components under the coupling conditions of bubble-type impurities and bubble-type impurities is studied.By changing the incident laser energy,bubble parameters,and bubble group parameters,the influence and law of bubble-type impurity defects on the temperature rise,stress,and optical field distribution of fused quartz materials are explored.Secondly,the optical field distribution in the backward region of the bubble will show an enhancement phenomenon,and the optical field will produce an amplification effect.The incident laser energy and bubble radius size are important influencing factors for this phenomenon.When two bubbles are superimposed and coupled,in addition to the size of the bubble radius,the distance between the bubbles also becomes an important factor that cannot be ignored in affecting the internal optical field amplification of fused quartz.The maximum value of the modulated optical field appears at a distance of 1 times the laser wavelength,and the coupling effect between bubbles disappears when the distance reaches 6 times the wavelength.Furthermore,the maximum value of the modulated optical field is related to the distance between the two bubbles,and the distance between the bubbles corresponding to the maximum value of the modulated optical field is also related to the incident laser wavelength.In terms of experimental research,in order to obtain the law of millisecond laser-induced damage of fused silica with defects,a control group was set up to study the changes of temperature,off-line stress,plasma and combustion waves and damage morphology of fused silica materials under different laser energy densities and pulse widths,and the effects of single-bubble type impurities and double-bubble type impurities on the damage of fused silica components were compared.This paper combines the results of theoretical,simulation and experimental studies to illustrate the damage process of fused silica components in millisecond pulsed laser systems caused by variations in laser parameters and their own defect parameters and summarizes the laws and characteristics.