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Surface damage on fused silica optics initiated by high fluence 351 nm laser is one of the major bottlenecks for the high power laser systems, such as, Shenguang Ⅲ (SG-Ⅲ) laser facility. Generally, the CO2 laser, which is strongly absorbed by fused silica and thus can effectively heat fused silica above melting temperature, is used to locally mitigate the damages, called the non-evaporative mitigation method. However, subsurface bubbles may be introduced in the damage mitigation process by CO2 laser melting. Unfortunately, the mitigated damage sites with subsurface bubbles can be easily re-initiated upon subsequent laser shots. In this article, in order to eliminate the subsurface bubbles, we systematically investigate the influences of mitigation protocols in different ways of laser irradiation preheating on the formation and control of subsurface bubbles. Based on the simulated results of the temperature distribution and structural changes under CO2 laser irradiation, two CO2 laser-based non-evaporative mitigation methods are proposed, which are adopted for the mitigation of surface damage sites ranging in size from 150 m to 250 m, and systematically investigated to assess the effect of eliminating subsurface bubbles. The process of mitigation method I is that multiple laser irradiations with short time and increasing power are initially used to preheat the damage site and then a higher power laser irradiation is adopted to mitigate the damage site. The process of mitigation method Ⅱ is that a long time, low power laser irradiation is first used to preheat the damage site and then a high power laser irradiation is adopted to mitigate the damage site. The detailed morphologies of the mitigation sites and subsurface bubbles produced by the two mitigation methods are measured by optical microscope with high magnification. A large number of small subsurface bubbles are observed in mitigation method I. While, less subsurface bubbles are observed in mitigation method Ⅱ. The statistical results indicate that among the thirty-four mitigated sites, only eight have no surface bubbles in method I. In contrast, among the fifty-four mitigated sites, forty-nine have no surface bubbles in mitigation method Ⅱ. The experimental results suggest that the formation probability of subsurface bubbles is effectively suppressed by the mitigation method Ⅱ. The mechanism of eliminating subsurface bubbles in the mitigation method Ⅱ is discussed based on the structural changes of the fused silica in the mitigation process. It is found that the fused silica is not melted by the long time, low power laser irradiation, which means that a long time preheating without melting could provide enough time to effectively reject air and impurities enwrapping in cracks, and thus reducing the formation probability of subsurface bubbles in the form of the crack closing due to rapid melting. With the mitigation method Ⅱ, the probability of mitigated sites without subsurface bubbles can reach 98%.

A series of FexSn100-x granular alloy films with different atomic fractions were fabricated by ion beam sputtering. The highest value ever observed for ferromagnetic metal/non-magnetic metal systems has been obtained. The extraordinary Hall effect was studied systemically by varying the atomic fractions and the thickness of the samples. With the power law between the saturated Hall resistivity and the resistivity the mechanism of the extraordinary Hall effect was also discussed.

There is a special area in KTP crystal, in which the SHG efficiency is obviously increased. In this paper, the KTP crystal is studied by means of Synchrotron Radiation (SR) White Beam Topography, and a planar defect is found in such an area. The lattice is deformed because of the accumulation of impurity in this area, which results in the increase of SHG efficiency. The maximum strain direction is determined to be R=〈010〉 according to the extinction condition of planar defect.

Dislocations and stacking faults in silicon webs were observed and analysed by means of X-ray projection topographic method. Large area stacking faults parallel to the web surface have been found in as-grown specimens. In addition to the edge-, screw-, and 60°-type total dislocations with Burgers vector 1/2, and edge-type Shockley partial dislocations with Burgers vector 1/6, 30°- and 60°-type Shockley partial dislocations with Burgers vector 1/6 have also been discovered in the webs. These total dislocations move during heat treating at high temperatures and interact with other ones to form nearly hexagonal dislocation networks. Several dislocation reactions in a single slip plane have been found. The configuration and contrast of stacking faults in as-grown webs were changed by high temperature annealing. That can be explained by the moving of extended dislocation pairs, and the overlapping of stacking faults with each other in different layers. The extinction rule of image of Shockley partial dislocations was invalidated by the presence of impurity segregations. Dislocations within the stacking fault image were also observed. The experimentally observed results were analysed and discussed briefly.