Local CO2 laser treatment has proved to be an effective method to prevent the 351-nm laser-induced damage sites in a fused silica surface from exponentially growing, which is responsible for limiting the lifetime of o...Local CO2 laser treatment has proved to be an effective method to prevent the 351-nm laser-induced damage sites in a fused silica surface from exponentially growing, which is responsible for limiting the lifetime of optics in high fluence laser systems. However, the CO2 laser induced ablation crater is often surrounded by a raised rim at the edge, which can also result in the intensification of transmitted ultraviolet light that may damage the downstream optics. In this work, the three-dimensional finite-difference time-domain method is developed to simulate the distribution of electrical field intensity in the vicinity of the CO2 laser mitigated damage site located in the exit subsurface of fused silica. The simulated results show that the repaired damage sites with raised rims cause more notable modulation to the incident laser than those without rims.Speeifically,we present a theoretical model of using dimpled patterning to control the rim structure around the edge of repaired damage sites to avoid damage to downstream optics. The calculated results accord well with previous experimental results and the underlying physical mechanism is analysed in detail展开更多
One of the main factors of laser induced damage is the modulation to incident laser which is caused by the defect in the subsurface of the fused silica. In this work, the repaired damage site irradiated by CO2 laser i...One of the main factors of laser induced damage is the modulation to incident laser which is caused by the defect in the subsurface of the fused silica. In this work, the repaired damage site irradiated by CO2 laser is simplified to a Gaussian rotation according to the corresponding experimental results. Then, the three-dimensional finite-difference time-domain method is employed to simulate the electric field intensity distribution in the vicinity of this kind of defect in fused silica front subsurface. The simulated results show that the modulation is notable, the Emax is about 2.6 times the irradiated electric field intensity in the fused silica with the damage site （the width is 1.5 μm and depth is 2.3 μm） though the damage site is repaired by CO2 laser. The phenomenon and the theoretical result of the annular laser enhancement existed on the rear surface are first verified effectively, which agrees well with the corresponding experimental results. The relations between the maximal electric field intensity in fused silica with defect depth and width are given respectively. Meanwhile, the corresponding physical mechanism is analysed theoretically in detail.展开更多
The abundant water resources, rainy climate and dense water network had deeply influenced the formation and development of traditional villages in the southern Hunan region of China. This paper was adopted b...The abundant water resources, rainy climate and dense water network had deeply influenced the formation and development of traditional villages in the southern Hunan region of China. This paper was adopted buffer zone analysis, categorical statistical analysis, vectorization analysis and data literature analysis, studied the shaping of traditional village site selection, plane form and internal spatial structure by water systems in southern Hunan, China, and the mechanism of their effects. The results showed that: 1) The shaping ability and mechanism of the traditional village water system in Xiangnan area on spatial morphology was mainly based on the function of the water system. 2) The layout and spatial morphology of traditional villages were deeply affected by the width, area and form of water systems in Xiangnan area. 3) Traditional villages gave more consideration to water systems with large watershed areas in site selection. 4) Water systems with small watershed areas generally had a greater impact on the internal structure of traditional villages.展开更多
基金supported by the Fundamental Research Funds for the Central Universities (Grant No. ZYGX2010J045)the National Natural Science Fundation of China and the China Academy of Engineering Physics United Foundation (NSAF) (Grant No. 11076008)the Foundation for Young Scholars of University of Electronic Science and Technology of China (Grant No. L08010401JX0806)
文摘Local CO2 laser treatment has proved to be an effective method to prevent the 351-nm laser-induced damage sites in a fused silica surface from exponentially growing, which is responsible for limiting the lifetime of optics in high fluence laser systems. However, the CO2 laser induced ablation crater is often surrounded by a raised rim at the edge, which can also result in the intensification of transmitted ultraviolet light that may damage the downstream optics. In this work, the three-dimensional finite-difference time-domain method is developed to simulate the distribution of electrical field intensity in the vicinity of the CO2 laser mitigated damage site located in the exit subsurface of fused silica. The simulated results show that the repaired damage sites with raised rims cause more notable modulation to the incident laser than those without rims.Speeifically,we present a theoretical model of using dimpled patterning to control the rim structure around the edge of repaired damage sites to avoid damage to downstream optics. The calculated results accord well with previous experimental results and the underlying physical mechanism is analysed in detail
基金Project supported by the National High Technology Research and Development Program of China (Grant No.2008AA8040508)the Youth Foundation of University of Science and Technology of China (Grant Nos.L08010401JX0834 and L08010401JX0806)the Fundamental Research Funds for the Central Universities of China
文摘One of the main factors of laser induced damage is the modulation to incident laser which is caused by the defect in the subsurface of the fused silica. In this work, the repaired damage site irradiated by CO2 laser is simplified to a Gaussian rotation according to the corresponding experimental results. Then, the three-dimensional finite-difference time-domain method is employed to simulate the electric field intensity distribution in the vicinity of this kind of defect in fused silica front subsurface. The simulated results show that the modulation is notable, the Emax is about 2.6 times the irradiated electric field intensity in the fused silica with the damage site （the width is 1.5 μm and depth is 2.3 μm） though the damage site is repaired by CO2 laser. The phenomenon and the theoretical result of the annular laser enhancement existed on the rear surface are first verified effectively, which agrees well with the corresponding experimental results. The relations between the maximal electric field intensity in fused silica with defect depth and width are given respectively. Meanwhile, the corresponding physical mechanism is analysed theoretically in detail.
文摘The abundant water resources, rainy climate and dense water network had deeply influenced the formation and development of traditional villages in the southern Hunan region of China. This paper was adopted buffer zone analysis, categorical statistical analysis, vectorization analysis and data literature analysis, studied the shaping of traditional village site selection, plane form and internal spatial structure by water systems in southern Hunan, China, and the mechanism of their effects. The results showed that: 1) The shaping ability and mechanism of the traditional village water system in Xiangnan area on spatial morphology was mainly based on the function of the water system. 2) The layout and spatial morphology of traditional villages were deeply affected by the width, area and form of water systems in Xiangnan area. 3) Traditional villages gave more consideration to water systems with large watershed areas in site selection. 4) Water systems with small watershed areas generally had a greater impact on the internal structure of traditional villages.
