| Optical components with characteristic of typical defective surface topography or contaminants adsorbing on the surface are easily damaged contributing to the highly laser irradiation.The damage threshold of fused silica optics will drop sharply as the degree of contamination deepens.Once the surface of the optical components is adhered by organic contaminants,it is rather difficult to purge and eliminate them and reach the cleanliness specification on the surface of optics.And this indicates that it is quite indispensable to dig into adhesion mechanism of contaminants on optical lenses at micro/nano-scale.Fused silica—the most commonly used optical components at high-power laser systems—is exploited deeply as the main research object.By means of simulation with application of molecular dynamics theory and characterization approach using of spherical harmonics method,the adsorption regularity and wettability of a number of representative topological nanostructure surfaces are investigated in allusion to thorny conundrums that residual contaminants on the optical surface can easily bring about serious damage to the system during the target shooting experiments,which are in favor of realization of exploration about medium-range order inside structure geometry of fused silica and are propitious to furnish basic theory and technical support for establishment of self-cleaning structural functional surface and development of cleaning technology.First of all,the research thought-way of this essay are obtained and verified via elaborating for reference the precision measurement method of decomposing the surface geometry morphological error,biological research of excellent and robust bio-surface micro/nano-composite structure morphology and crystallographic study of quasicrystal and metallic glass.It is elaborately determined through the research spatial micro/nano-scale that theory based of the simulational analysis is molecular dynamics.And then,the clusters of water molecules and ring-shaped oil molecules are respectively built on a smooth flat fused silica substrate to make a confirmation of correctness of model scientific method.Subsequently,it shows that the polar end of the oil molecule is firmly attached to well-type nano-structure on surface of the fused silica by inspecting the adhesion state of annular oil molecules on the surface.Based on study idea method that any surface can be decomposed into a linear superposition of different sinusoidal surfaces,software is applied to build sinusoidal nano-structure array surfaces with various amplitudes and frequencies,and then,add water clusters to top of the established substrate model to simulate adsorption interaction.Through combining the contact angle of water droplets,mass density distribution and height of the center of mass of water clusters,at the same time,by comparing the different topological surface with the rectangular groove and square columnar surface array of fused silica dynamic adsorption course on the surface of different nano-structures are explored,steady-state surface wettability and cluster pattern analyzed,effect law of different morphological characteristics on the surface of fused silica ultimately obtained.Whereafter,the radial distribution function method is used to verify the rationality of the model that is named as the bulk fused silica material constructed by MD method.By way of theoretical derivation of the spherical harmonic function formula and C++program compiling routine to proceed mathematical statistics of the nano-structure of inner fused silica,it is found that the number of neighboring atoms of most atoms within the range of 0.25nm≤rcutoff≤0.35nm is 4 or 8.Meanwhile,it is found that 39.95%of the atoms in fused silica are"medium-range order"and“icosahedral quasicrystals”account for the largest proportion of ordered geometric configurations when commanding 0.3nm as the research radius.A visual comparative analysis of typical icosahedral quasi-crystals exhibits that existent explanation of this geometric configuration type is that atoms in the peripheral tetrahedral configuration become neighboring atoms within the cut-off radius of the central oxygen atom due to the spatial geometric configuration of fused silica which retains the disorder of liquid.Subsequently,after constructing the fused silica quasicrystal model,the wettability of this pattern surface and the adhesion mechanism of oil molecules on icosahedral quasi-crystals are analyzed in detail.Finally,author of this article determined the method of dry etching technique using neutral loop discharge approach,and then,successfully fabricated a groove-shaped micro-structure array on the surface of high-hardness and corrosion-resistant optical components.White-light fiber interferometer are used to characterize and verify the processed microstructure morphology that basically meets the design requirements.The surface wettability of 45 different micro-structure sizes prepared were experimentally measured and counted by contact angle meter.And by integrating with simulational analysis,the adsorption of water droplets on the surface of the optical components both are in the shape of water column.And as the slot pitch of the structural unit or the size of the unit varies,the simulation result is consistent with the wettability variation regularity measured by the experiment. |
