Research On The Laser Repairment Dynamics Of Optical Defects In Fused Silica Components

In order to use CO₂ laser repair fused silica damage in theoretical simulation,we must first build repair of fused silica damage physical process and the geometric model of different damage morphology.Research in different sizes of damage under the same laser parameters of thermodynamics and dynamics process;Research in different laser parameters under the same sizes of damage of thermodynamics and dynamics process.Fused silica which is one of most important reason to limit the fluence of laser facilities.Control damage growth is an important means to raise damage capacity of high power laser facilites.Among the many methods to repair surface damage of fused silica,the methods of CO₂ laser repair has been widely accepted.On the physical process of this method the theoretical analysis and numerical calculation has been done.In this paper,the main studies contents and conclusions are as follows:1.Summarizes the characteristics of fused quartz surface damage and type.It turned out that from damage morphology,it can be divided into the scratch type,pitting type,hole type;From the properties of damage formation,it can be divided into brittleness,plasticity and mixed type.Morphology of the damage points is directly related to the laser speckle shape,size and spatial distribution.Based on damage morphology,geometrical models are established,Using the flow and mutual coupling heat transfer way to establish two-dimensional melt flow model for CO₂ laser irradiation fused silica component,In theory,quantitative description of the characteristics of morphology after fused silica component has been repaired.2.The influence of laser parameters on the damage morphology and repair size has been analysed with the finite element method.The results show that during CO₂ laser repair process,the outline of melting and evaporation area all present gaussian pits morphology,irradiation time,spot size and laser power have great influence to the repair results.The influence of pulse frequency to repair the size is not obvious,but the increase in frequency can significantly decrease the size of evaporation,and has little impact on molten size change,To reduce evaporation to make repair surface more smooth,this is consistent with the experimental results.3.Temperature distribution and evolution of fused silica component irradiated by Gaussian laser are calculated.when the laser irradiation end,the temperature in the spot center is highest.The surface temperature gradient is small and the isotherm is round,but in the internal component isotherm is Gaussian-shaped and temperature gradient is more large.And the isotherms have smaller depth and larger width.During heating and cooling process,Temperature are quickly change before they are slow near the spot edge the temperature gradient is more larger.4.The creep theory is introduced to the high temperature annealing effect that has been calculated.The simulated result show that after high-temperature annealing the residual stress in the component can be effectively reduced.But,creep is related to the stress,it's have a negative impact on the morphology.Furthermore,By comparing the large-diameter fused silica component of annealing can prove that side support with vertical surfaces can effectively mitigate the effect of weight on morphology.5.Thermal stress distribution of component irradiated by laser are calculated,and how the laser parameters affect the residual stress.In the irradiation area compressive stress is generated during irradiation and tensile stress is generated at peripheral area,the cooling process is reverse.Primary stress at the center of the light spot on the surface of the element arranged in concentric ring as the center,irradiation center materials of the largest tensile stress are located around the irradiation center.Shear stress on the surface of the element is symmetrical about irradiation center,The maximum shear stress is located in the edge of irradiation,there are four a high stress area,all showed fusiform.Maximum radius of residual shear stress has no related with laser power and irradiation time but the beam radius,his is consistent with the experimental results.6.The effect of laser power,time,beam diameter on melt flow have been calculated.The result shows that the as the time increases,the flow rate increases rapidly.and,the depth of the pit and the height of the convex ring also increased rapidly.In addition,the flow velocity is almost same,under the same maximum temperature.As laser power and beam size change,the depth and whidth of Gaussian pit,height of raised ring are all increased differently.But,the depth of pit and convex ring height are sensitive to laser power,and the width of Gaussian pit is sensitive to beam size.