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The isotopic composition of water in Earth's oceans is challenging to recreate using a plausible mixture of known extraterrestrial sources such as asteroids -an additional isotopically light reservoir is required. The Sun's solar wind could provide an answer to balancing Earth's water budget. We used atom probe tomography to directly observe an average ~1 molecular percent enrichment in water and hydroxyls in the solar wind irradiated rim of an olivine grain from the S-type asteroid Itokawa. We also experimentally confirm that H irradiation of silicate mineral surfaces produces water molecules. These results suggest that the Itokawa regolith could contain ~20 litres per m 3 of solar wind derived water and that such water reservoirs are likely ubiquitous on airless worlds throughout our galaxy. The production of this isotopically light water reservoir by solar wind implantation into fine grained silicates may have been a particularly important process in the early Solar System, potentially providing a means to recreate Earth's current, water-isotope ratios. Main Text:The origin of Earth's water and volatile budget is a topic of considerable debate in planetary science [1][2][3][4][5][6][7][8][9][10] . Most current dynamical models of Earth's formation assume that the majority of Earth's water and other volatiles was added later from an exogenous source 1-4 . That volatile source shared a common parent population with C-type asteroids, that is likely located in the Jupiter-Saturn region and beyond [11][12][13][14] . C-Type asteroids are thought to be the parent bodies of carbonaceous (C) chondrite meteorites as they exhibit similar reflectance spectra, in particular the CRs, CMs and CIs 15 , which can contain up to 10 weight percent (wt. %) H 2 O (Table 1) 9 . Although the D/H isotope ratios of C-chondrite meteorites are a closer fit to the Earth than to comets or other meteorite types, with CMs being a particularly close match (Table 1) 2,16 , the Earth's mantle and Standard Mean Ocean Water (SMOW) are lighter in D/H 17 than the average of CI-, CR-and CM-chondrite groups [e.g., 1,16,18 Table 1]. Given the diversity of water rich C-chondrites in the meteorite record, it is unlikely that CM-like asteroids alone delivered all of Earth's water. Thus, as they are the most water-rich meteorites 9 , the CIs, CRs and CMs are believed to represent the majority of Earth's chondritic water component. Although recent studies of nominally anhydrous minerals from enstatite chondrites 10 and Itokawa particles 19 suggests that these materials may be more water-rich than previously thought, they only contain sufficient water for the lowest estimate of Earth's water budget (Table 1). D/H ratios of the Earth's deep mantle are even lighter than SMOW (Table 1) 2 ; recent analysis of volcanically exhumed material indicate that a component of 4 isotopically-light, solar-like D/H may be extant in the primitive mantle (Table 1) 6 . In addition, the bulk D/H ratio of the Earth may have increased from its initial value over the last 4.5...

Growing laser damage sites on multilayer high reflector coatings can limit mirror performance.One of the strategies to improve laser damage resistance is to replace the growing damage sites with pre-designed benign mitigation structures. By mitigating the weakest site on the optic, the large aperture mirror will have a laser resistance comparable to the intrinsic value of the multilayer coating. To determine the optimal mitigation geometry, the finite difference time domain method (FDTD) was used to quantify the electric-field intensification within the multilayer, at the presence of different conical pits. We find that the field intensification induced by the mitigation pit is strongly dependent on the polarization and the angle of incidence (AOI) of the incoming wave. Therefore the optimal mitigation conical pit geometry is application specific. Furthermore, our simulation also illustrates an alternative means to achieve an optimal 2 mitigation structure by matching the cone angle of the structure with the AOI of the incoming wave, except for the p-polarization wave at a range of incident angles between 30 and 45 .