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.

Irradiation effects of CO 2 laser parameters on surface morphology of fused silica * Xiang Xia(向 霞) a)b) , Zheng Wan-Guo(郑万国) a) , Yuan Xiao-Dong(袁晓东) a) † , Dai Wei(戴 威) a)b) , Jiang Yong(蒋 勇) a)b) , Li Xi-Bin(李熙斌) a) , Wang Hai-Jun(王海军) a) , Lü Hai-Bing(吕海兵) a) , and Zu Xiao-Tao(祖小涛) b)a)

The microstructure, optical property and magnetism of nitrogen ion implanted single MgO crystals are studied. A parallel investigation is also performed in an iron ion implanted single MgO sample as a reference. Large structural, optical and magnetic differences are obtained between the nitrogen and iron implanted samples. Room temperature ferromagnetism with a fairly large coercivity field of 300 Oe (1 Oe=79.5775 A/m), a remanence of 38% and a slightly changed optical absorption is obtained in the sample implanted using nitrogen with a dose of 1×10 18 ions/cm 2 . Transition metal contamination and defects induced magnetism can be excluded when compared with those of the iron ion implanted sample, and the nitrogen doping is considered to be the main origin of ferromagnetism.

Structural, electronic and magnetic properties of the Mn Ni(110) c(2×2) surface alloy * Li Deng-Feng(李登峰) a)b) † , Xiao Hai-Yan(肖海燕) b) , Zu Xiao-Tao(祖小涛) b) , Dong Hui-Ning(董会宁) a) , and Gao Fei(高 飞) c)

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