基于傅里叶模方法的KDP晶体镀膜减反技术

 采用傅里叶模方法,分析了单点金刚石铣削后KDP晶体表面小尺度波纹的周期和幅值对单层增透膜折射率、厚度以及透射率的影响。研究表明：膜层最佳折射率在1.22左右,在此折射率条件下,保证透射率大于99%的单层增透膜的理想厚度范围应为180~220 nm,并且折射率和膜厚值的选取基本不受晶体表面小尺度波纹周期和幅值的影响。若只考虑SPDT法加工后KDP晶体表面小尺度波纹周期和幅值的实际范围,透射率基本不受波纹周期的影响,但却会随波纹幅值的增大而加速下降。理想镀膜条件下透射率最大值大于99%,并且通常在99.67%~99.94%之间。     

KDP晶体金刚石车削参数对晶体雾化的影响

安装在高功率激光系统中的KDP晶体,其表面质量是一个很重要的问题。单点金刚石车削是唯一获得透射波前误差和激光损伤阈值的方法,尤其是在紫外UV波段。KDP晶体表面雾化与金刚石车削参数有关。研究金刚石车削参数主要是为了提高KDP晶体的频率转化效率。研究结果表明,在金刚石切削中使用一种纯净的切削油和适宜的加工参数能大大地减少晶体表面的雾化。     

小尺度波纹对KDP光学元件透射比的影响

高精度KDP晶体是惯性约束核聚变光路系统中的重要元件,而已加工表面的小尺度波纹对光学元件的透射比有着重要影响。采用傅里叶模方法理论分析了表面小尺度波纹的幅值及周期对KDP光学元件透射比的影响。研究结果表明,当小尺度波纹幅值小于100 nm时,透射比随波纹幅值的增加基本呈线性增长,波纹幅值每提高10 nm.透射比可提高近0.5%;透射比随着小尺度波纹周期的增加围绕中心透射比上下浮动,透射比振幅基本保持不变.且中心透射比及透射比振幅均随着小尺度波纹幅值的增加而增大;小尺度波纹周期在10.5～12μm区间内时透射比明显很低,需采取措施避免小尺度波纹的周期出现在此区间。对KDP晶体进行了加工、表面形貌检测及透射比检测的实验,实验结果与理论计算结果基本吻合。     

冲击波实验用铝楔形靶加工技术

采用单点金刚石车削技术制备加工铝楔形靶,发现金刚石车削加工楔形靶实际轮廓为圆锥面。通过Veeco NT1100白光干涉仪对表面轮廓及粗糙度进行了测量,结果表明平面部分表面粗糙度小于50 nm,最大峰谷值小于100 nm,斜面部分表面粗糙度小于200 nm。分析认为斜面部分粗糙度测量数值较大是由刀具工作角度变化导致的,而测量轮廓线非圆锥体母线又导致粗糙度测量结果大于实际值。     

KDP晶体单点金刚石切削表面粗糙度预测及实验研究

采用单点金刚石切削的方法加工了KDP晶体,利用回归分析的方法建立了表面粗糙度预测模型,达到了在加工前设计、预测和控制表面粗糙度的目的。利用预测模型分析了进给量、切削速度、背吃刀量对表面粗糙度的影响。通过优化设计获得了KDP晶体在该条件下的最佳切削参数,得到的表面粗糙度的最佳估计值为6.3389nm。利用最佳的切削工艺参数,加工出了表面粗糙度值为6.895nm的超光滑表面。     

切削参数对KDP晶体加工表面实际频率特征的影响

针对采用单点金刚石超精加工的KDP晶体光学表面,研究了切削参数对微观形貌频率特征的影响。通过功率谱密度获得表面轮廓频率分布,并用连续小波重构加工过程中随切削用量变化的微观轮廓频率特征。结果表明:切削参数对微观形貌的影响具体表现在实际频率特征上,中频特征波长及幅值反映了切深及转速变化,随切深及转速增加,幅值变大;低频特征反映了进给量变化,随着进给量变小,频率及幅值变小;高频特征是加工过程中振动及材料各向异性的具体表现。     

规则表面形貌的分形和多重分形描述

以6种具有典型特征的生成元构造了6个具有相同rms粗糙度的规则表面,用变分法计算了这些表面的分形维数,结果表明,分形维数可以将具有相同rms粗糙度的表面区分开来,它定量表征了表面的总体形貌。进一步将多重分形的方法应用到对这些表面的分析中,发现多重分形谱可以全面反映表面概率的分布特征。多重分形谱的宽度可以定量表征表面的起伏程度,多重分形谱最大、最小概率子集维数的差别可以统计表面最大、最小概率处的数目比例。 关键词： 粗糙度 分形维数 多重分形谱     

高效光学加工技术

为验证国产大口径KDP晶体金刚石车床（图1）的加工能力，进行了多次试验。加工的φ150mm小于0．52的铝镜面已达到与俄罗斯机床同等水平。但同时进行的一轮KDP晶体车削试验，结果并不满意，其单次透射波前畸变近4λ，原因可能是KDP晶体的装夹存在问题，导致加工效率不佳。而且加工中还产生周期性波纹，可能是由于机床压缩空气供给系统的周期性启动，造成周期性的压力波动。     

粗糙表面形貌对微尺度流动换热的影响

基于分形几何定量描述了多尺度自仿射的粗糙表面形貌,建立了微通道内层流流动换热的理论模型并对表面形貌的影响进行了数值模拟.研究表明,自仿射分形维数直接反映了表面轮廓的不规则度,对于两个具有相同统计粗糙度的轮廓,可能存在不同的分形维数;与常规尺度通道不同,雷诺数、粗糙高度和粗糙表面分形维数都对微通道内层流流动换热有着重要影...     

CaF2衍射光学元件的金刚石车削工艺优化

为了提高单点金刚石车削CaF2衍射光学元件(DOE)的表面质量和衍射效率,首先基于Beckman标量散射理论和有效面积法,建立了表面粗糙度误差和表面轮廓误差对衍射效率影响的数学模型.然后,结合CaF2的车削特性和DOE的结构特点,优化了CaF2 DOE的车削模型.同时,给出了不同工艺条件下半圆金刚石刀具的最佳车削位置和最优刀具半径,实现了对CaF2 DOE表面粗糙度的控制.最后,在该优化模型的指导下,获得了表面粗糙度为3.4 nm、阴影区域宽度为28.7μm的高表面质量的CaF2 DOE,验证了所提优化车削模型的可靠性.所提车削模型对提高包含CaF2 DOE折-衍混合光学系统的成像质量具有重要意义.     

Modification of three dimensional topography of the machined KDP crystal surface using wavelet analysis method

The wavelet analysis method has been extensively employed to analyze the surface structures and evaluate the surface roughness. In this work, however, the wavelet analysis method was introduced to decompose and reconstruct the sampled surface profile signals in the cutting direction that achieved by SPDT (single point diamond turning) operation, and the surface profile signals in tool feeding direction were reconstructed with the approximate harmonic functions directly. And moreover, the orthogonal design method, i.e. the combination design of general rotary method, was resorted to model the variations of the independent frequency and amplitude of different simulated harmonic signals in the cutting and tool feeding directions. As expected resultantly, a novel 3D surface topography modeling solution was established, which aims to predict and modify the finished KDP (potassium dihydrogen phosphate or KH₂PO₄) crystal surfaces. The validation tests were carried out finally under different cutting conditions, and the collected average surface roughness in any case was compared with the corresponding value as predicted. The results indicated the experimental data were well consistent with the predictions, and only an average relative error of 11.4% occurred in predicting the average surface roughness.     

KDP晶体微纳米加工表层缺陷对其激光损伤阈值的影响

使用有限元方法分析了在激光辐照条件下,KDP晶体已加工表面存在的残余内应力、微裂纹及微孔等多种微纳米加工表层缺陷对晶体激光损伤阈值的影响。通过分析发现:KDP晶体微纳米加工表层缺陷的存在,会影响晶体表面的温度场及热应力场的分布,使入射激光的能量积聚在缺陷附近的很小范围内,造成晶体缺陷处产生局部熔融现象,从而使KDP晶体产生损伤,降低KDP晶体的激光损伤阈值。针对微纳米表层的微裂纹进行了损伤阈值测试实验,结果表明微裂纹的存在会降低KDP晶体的激光损伤阈值(约降低3J/cm2),实验结果与仿真结果符合得很好。     

断裂表面自相似与自仿射复杂分形结构的研究

 按照分形理论研究了具有自相似和自仿射分形结构的复杂表面,并研究了其在Ⅰ型+Ⅱ型和Ⅰ型+Ⅲ型混合载荷下形成的断裂表面的应用。结果指出：分维D与粗糙度指数H之间的关系（D+H=2或D×H=1）只是粗略的近似。用分维D或粗糙度指数H测量断裂表面,在双对数图上得到的是实验曲线而不是直线并不说明没有分形结构,很可能是自相似和自仿射结构的混合。     

Fractal Analysis of Surface Roughness of Particles in Porous Media

A fractal dimension for roughness height （RH） is introduced to characterize the degree of roughness or disorder of particle surface characters which significantly influence physical-chimerical processes in porous media. An analytical expression for the fractal dimension of RH on statistically self-similar fractal surfaces is derived and is expressed as a function of roughness parameters. The specific surface area （SSA） of porous materials with spherical particles is also derived, and the proposed fractal model for the SSA of particles with rough surfaces is expressed as a function of fractal dimension for RH and fractal dimension for particle size distribution, relative roughness of particle surface, and ratio of the minimum to the maximum particle diameters of spherical particles.     

A Monte Carlo method for simulating fractal surfaces

A Monte Carlo method is presented for simulating rough surfaces with the fractal behavior. The simulation is based on power-law size distribution of asperity diameter and self-affine property of roughness on surfaces. A probability model based on random number for asperity sizes is developed to generate the surfaces. By iteration, this method can be used to simulate surfaces that exhibit the aforementioned properties. The results indicate that the variation of the surface topography is related to the effects of scaling constant G and the fractal dimension D of the profile of rough surface. The larger value of D or smaller value of G signifies the smoother surface topography. This method may have the potential in prediction of the transport properties (such as friction, wear, lubrication, permeability and thermal or electrical conductivity, etc.) on rough surfaces.     

Fractal structure of digital speckle patterns produced by rough surfaces

We report on the fractal analysis of digital speckle patterns experimentally generated using an optical setup to record the light scattered from metallic rough surfaces in the normal direction. Using the differential box counting technique, we have calculated the fractal dimension of digital speckle patterns for six samples with different roughness. Our results show a quadratic dependence between the surface roughness and the fractal dimension of the corresponding digital speckle pattern. As an application a method to determine the surface roughness of metallic surfaces is proposed.     

Discrete dipole approximation simulations of light reflection from flat non-transparent particles with rough surfaces

We study light reflection from flat particles with rough surfaces and fractal statistics of topography. Discrete dipole approximation method is used to solve the problem of light scattering. Refractive indices corresponding to a metal and a transient material with conductive properties are taken. The sizes of particles are much larger than the wavelength of incident light and the roughness scales are larger, comparable to and smaller than the wavelength. The influence of the fractal dimension parameter and the amplitude of heights of random topography on reflectance and on the angular profile of the specular reflection peak is considered. Our calculations demonstrate that topography amplitude is very important for reflectance and fractal dimension is responsible for the angular dispersion of the specular reflection peak.     

Influence of surface roughness on superhydrophobicity

Superhydrophobic surfaces, with a liquid contact angle theta greater than 150 degrees , have important practical applications ranging from self-cleaning window glasses, paints, and fabrics to low-friction surfaces. Many biological surfaces, such as the lotus leaf, have a hierarchically structured surface roughness which is optimized for superhydrophobicity through natural selection. Here we present a molecular dynamics study of liquid droplets in contact with self-affine fractal surfaces. Our results indicate that the contact angle for nanodroplets depends strongly on the root-mean-square surface roughness amplitude but is nearly independent of the fractal dimension D(f) of the surface.