【摘要】：對CO_2激光修復(fù)熔石英元件損傷的理論上的計(jì)算模擬,首先要建立修復(fù)元件損傷的物理過程的模型及對不同損傷形貌的幾何模型。研究在同一激光參數(shù)下不同損傷尺寸的熱力學(xué)和動力學(xué)過程;研究在同一損傷尺寸不同激光參數(shù)下的熱力學(xué)和動力學(xué)過程。作為高通量段固體激光裝置的首選材料熔石英,由激光導(dǎo)致的損傷依然是限制CO_2激光通量的主要因素。抑制元件表面損傷增加,是提高激光裝置負(fù)載能力的一個重要方法。在眾多修復(fù)損傷的方法中,普遍認(rèn)同CO_2激光的修復(fù)效果,針對這種修復(fù)方案的物理過程展開了理論分析及數(shù)值計(jì)算,本文研究的主要內(nèi)容及結(jié)論如下:1.總結(jié)了熔石英表面損傷的特點(diǎn)、類型。結(jié)果表明:可以從損傷形貌上將其劃分為劃痕型、麻點(diǎn)型、坑洞型等幾種。從形成屬性上可分為脆性、塑性以及兩種屬性相混的損傷形貌。損傷點(diǎn)的形貌與CO_2激光光束形狀、大小和空間分布有直接關(guān)系。對常見的元件表面損傷形貌進(jìn)行建模,運(yùn)用傳熱和流動的耦合來確立激光輻照熔石英元件的熔融模型,定量的描述了熔石英元件修復(fù)過程中的表面特征。2.只改變一種CO_2激光的參數(shù),保持其它參數(shù)不變情況下,探討了多種激光參數(shù)對修復(fù)不同損傷形貌的結(jié)果。結(jié)果顯示修復(fù)后的形貌,基本外形呈現(xiàn)高斯坑形,對修復(fù)結(jié)果的影響比較顯著的激光參數(shù)有:激光輻照時間、光束形狀和功率。脈沖頻率對修復(fù)尺寸的影響則不大,但增加頻率可顯著的緩解熔石英材料的蒸發(fā),而對熔石英材料的熔融區(qū)域影響不大,可使元件修復(fù)后的表面更加光滑。和現(xiàn)有的實(shí)驗(yàn)結(jié)論相符合。3.計(jì)算了高斯形光束輻照熔石英元件的溫度的演化過程和溫度分布。剛修復(fù)后,最高溫度位于光斑中心,并由中心向外梯度下降,溫度在材料表面的下降速度較快,而溫度在材料內(nèi)的的下降速度則較慢,材料表面的等溫線呈環(huán)形,而元件內(nèi)的等溫線的深度相對較小、寬度相對較大。在修復(fù)過程中和和修復(fù)后的冷卻降溫過程中溫度變化均是先快速降低,然后減緩。4.在模擬修復(fù)后冷卻過程中采用蠕變理論來分析,用該理論分析熔石英材料的退火過程中的應(yīng)力。通過模擬可知該理論可有效的分析退火過程中的應(yīng)力。此外,通過對比可以發(fā)現(xiàn)在退火過程中可以用大光束的激光,這有利于提高熔石英元件修復(fù)后的表面光滑程度。5.計(jì)算了激光輻照元件的熱應(yīng)力的分布與演化,及激光參數(shù)如何影響應(yīng)力分布。CO_2激光輻照過程中光斑所在區(qū)會產(chǎn)生壓應(yīng)力,而在光斑之外產(chǎn)生拉應(yīng)力,修復(fù)后的降溫過程恰恰相反。材料表層的主應(yīng)力關(guān)于光斑中心呈圓形分散開,光束中心元件表面的最大拉應(yīng)力處于光束外圍。而材料表面的最大剪切應(yīng)力有四個,它們關(guān)于光束的圓心對稱,并且位于輻照邊緣,形狀相似。此外殘余剪切應(yīng)力的最大半徑只與激光光束的半徑有關(guān),和現(xiàn)有的實(shí)驗(yàn)結(jié)論相符合。6.模擬計(jì)算了光束半徑、激光功率、輻照時間三個激光參數(shù)如何影響修復(fù)過程中材料在熔融時的流動,結(jié)果顯示,隨輻照時間的延長,熔融材料的流速迅速上升,同時,凸起環(huán)高度和高斯坑深度也快速增加。此外,在元件相同的最高溫度情況下,改變光束半徑和激光功率對的流速影響均較小。隨著激光單位面積功率增大,凸起環(huán)高度、高斯坑深度、寬度均有不同程度增大,然而,激光功率對坑深和環(huán)高影響更顯著,而光束半徑對坑深和環(huán)高影響較弱,但對坑寬的影響卻較顯著。
[Abstract]:In the theoretical calculation and Simulation of CO_2 laser repairing fused silica damage, the physical process model and the geometric model of different damage morphology should be established firstly. Dynamics and dynamics. Laser-induced damage to fused silica, the preferred material for high-throughput solid-state laser devices, remains a major limiting factor for CO_2 laser fluxes. The main contents and conclusions of this paper are as follows: 1. The characteristics and types of surface damage of fused silica are summarized. The results show that the surface damage can be divided into scratch type, pit type, pit type and so on. For brittleness, plasticity and mixing of two properties, the morphology of the damage point is directly related to the shape, size and spatial distribution of CO_2 laser beam. The surface characteristics of the repaired parts were studied by changing the parameters of one CO_2 laser and keeping the other parameters unchanged. The results show that the repaired parts have Gaussian pit shape, and the laser parameters have significant influence on the repaired results. Time, beam shape and power. Pulse frequency has little effect on the repairing size, but the evaporation of fused silica can be significantly alleviated by increasing pulse frequency, and the melting area of fused silica can be neglected. The surface of repaired fused silica can be smoother. It is consistent with the existing experimental results. 3. Calculated the irradiation of fused silica with Gaussian beam. Temperature evolution and temperature distribution of the element. After repair, the highest temperature is located in the center of the facula and decreases from the center to the outside gradient. The temperature decreases faster on the surface of the material, but the temperature decreases slower in the material. The isotherms on the surface of the material are annular, while the depth and width of the isotherms in the element are relatively small. In the process of repairing and cooling process after repairing, the temperature changes decrease rapidly first, and then slows down. 4. In the process of cooling after repairing, creep theory is used to analyze the stress in the annealing process of fused silica materials. The stress in the process of annealing can be improved by using a large beam of laser. 5. The thermal stress distribution and evolution of the laser irradiated element and how the laser parameters affect the stress distribution are calculated. The principal stress on the surface of the material is circularly dispersed with respect to the center of the spot, and the maximum tensile stress on the surface of the element at the center of the beam is at the periphery of the beam. In addition, the maximum radius of residual shear stress is only related to the radius of the laser beam, which is consistent with the existing experimental results. 6. The effects of three laser parameters, beam radius, laser power and irradiation time, on the flow of the material in the melting process are simulated and calculated. With the increase of the laser power per unit area, the height of the convex ring, the depth of the Gaussian pit and the depth of the convex ring increase rapidly. However, the influence of laser power on pit depth and ring height is more significant, while the influence of beam radius on pit depth and ring height is weaker, but on pit width is more significant.
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TN249

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本文編號：2209623