精磨光学元件面形的干涉检测技术研究

为解决传统接触式检测方法检测精磨光学元件效率低,精度差的问题,提出了一种采用干涉检测技术对精磨光学元件面形进行测量方法,该方法具有非接触,测量效率高,误差小的特点。干涉检测中干涉条纹的对比度与工作波长成正比,与表面粗糙度成反比,干涉条纹对比度直接影响最终的检测结果。因此首先分析干涉条纹对比度与精磨表面粗糙度之间的关系,证明采用可见光干涉仪对精磨粗糙表面进行检测的可行性,并对利用GPI型数字干涉仪检测精磨粗糙表面进行了实验验证,检测面形结果约为PV 1.5μm,并与红外干涉仪以及接触式轮廓仪测量结果进行了对比,验证结果有效性。最后给出了当粗糙度阈值Rq优于150 nm时,可采用该方法进行检测,具有较高的实用价值。     

基于横向剪切的四向最小二乘相位解包裹算法

为了解决相位变换过快导 致相位离散梯度不连 续及解包裹中欠采样的出现,本文将横向剪切干涉技术引入到四向最小二乘相位解包裹算法 中。通过对包裹相位 建立二维复光场,对复光场进行剪切,一方面可以排除相位截断的干扰,另一方面剪切的引 入可以提高算法对严 重包裹相位的处理能力。实验结果表明,本文算对恢复相位信息有较好的 效果,同时具有四向 最小二乘的抑制误差传递的优点,且适合于对部分区域变化过大的相位进行解包裹。     

低噪声双波长数字全息及在超精密加工表面检测中的应用

通过两个不同波长的数字全息包裹相位差产生数字拍频,得到一个等效波长相位图以消除相位包裹,然后用该等效波长相位光程与任一记录波长做比较,确定单波长包裹相位中相位跳变的位置和跳变倍率,进而实现了单波长包裹相位展开,使相位噪声不随等效波长相位展开而放大,结果表明该方法可使相位噪声引入的误差减小2Λ/λm倍。用650 nm和632.8 nm两个波长的激光对用快刀伺服加工的微结构光学元件表面进行了数字全息测量,得到了等效波长为0.024 mm的加工纹理相位展开图,并用频谱滤波得到了元件微观形貌的低频和高频三维数据,各频段表面的粗糙度分别为33.2 nm,19.3 nm,23.4 nm,分析了各种微观结构产生的原因,并对快刀加工的切削参数进行了分析。     

Facile Morphological Qualification of Transferred Graphene by Phase-Shifting Interferometry

Post-growth graphene transfer to a variety of host substrates for circuitry fabrication has been among the most popular subjects since its successful development via chemical vapor deposition in the past decade. Fast and reliable evaluation tools for its morphological characteristics are essential for the development of defect-free transfer protocols. The implementation of conventional techniques, such as Raman spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy in production quality control at an industrial scale is difficult because they are limited to local areas, are time consuming, and their operation is complex. However, through a one-shot measurement within a few seconds, phase-shifting interferometry (PSI) successfully scans ≈1 mm² of transferred graphene with a vertical resolution of ≈0.1 nm. This provides crucial morphological information, such as the surface roughness derived from polymer residues, the thickness of the graphene, and its adhesive strength with respect to the target substrates. Graphene samples transferred via four different methods are evaluated using PSI, Raman spectroscopy, and AFM. Although the thickness of the nanomaterials measured by PSI can be highly sensitive to their refractive indices, PSI is successfully demonstrated to be a powerful tool for investigating the morphological characteristics of the transferred graphene for industrial and research purposes.     

Boundary detection of internal defect based on discontinuity of second-order gradient of out-of-plane displacement in phase-shifting digital speckle pattern interferometry

A new method for detecting the boundary of an internal defect is proposed in this paper. The proposed method can be used in phase-shifting digital speckle pattern interferometry to detect accurately the boundary of an internal defect based on discontinuity of the second-order gradient of out-of-plane displacement in the direction perpendicular to the defect boundary. Both theoretical analysis and experimental result are presented in this paper.     

Surface shape measurement of mirrors in the form of rotation figures by using point diffraction interferometer

The paper deals with the use of a point diffraction interferometer (PDI) to study the surface shape of rotation figures. The relations are given for the correspondence of the coordinates on the surfaces of an ellipsoid, a paraboloid and a hyperboloid as well as on an interferogram. Using PDI and Zygo white-light interferometer (WLI), we experimentally investigated the surface shape of the grazing incidence ellipsoid with the multilayer reflective coating on a wavelength of 0.154 nm with the following parameters: length is 55 mm, half-axis are 6 and 235 mm. The results coincided with an accuracy of 73 nm (RMS) without taking into account the PDI lateral resolution, and with an accuracy of 50 nm (RMS) with taking it into account, which ensures the local angles measurement accuracy of the ellipsoid-shaped reflecting surface at a level of 3 μrad. We think that this difference may be attributed to the limited lateral resolution of PDI and errors of frames stitching of WLI; nevertheless, we do believe that the PDI measurement accuracy is in the range of sub-μrad.     

Numerical and experimental studies on aluminum sandwich plates of variable thickness

Abstract

The elastic flexural behavior of static deformation and free vibration of sandwich plates of variable thickness is investigated numerically and experimentally. In the analysis, the face plates are treated as Marguerre shells, and the core is assumed to be an antiplane core and to provide resistance to transverse shear and normal stresses only. Displacement continuity conditions are used at the interfaces between face plates and the core to derive the displacement field. Energy formulations are obtained and solved by the isoparametric finite element method. The numerical results are obtained to compare with the results in the existing literature and to show the effects of taper constant and face plate thickness on deflections and natural frequencies. Finally, experimental works based on the method of holographic interferometry are conducted to confirm the theoretical findings. Experimental and numerical data agree quite well in this work.     

林分平均高度卫星遥感新进展

林分平均高度是生态系统模型重要的输入参数之一,与生物量估算与碳循环研究高度相关。通过系统回顾林分平均高度研究的发展历史和最新进展,总结了不同传感器林分平均高度(SAR树高与LiDAR冠层高度)研究的主要模型和方法,通过单一传感器技术进行林分平均高度研究的内在特征的不同,分析了多传感器的区域林分平均高度联合反演方法的优劣性,并从科学发展趋势和社会需求出发,认识目前存在的主要问题与难点及未来面临的挑战和机遇,为今后更好地进行森林垂直结构和全球碳循环研究提供思路和借鉴。     

Influence of low external magnetic field on electric field induced strain behavior of 9/70/30, 9/65/35 and 9/60/40 PLZT ceramics

In this work, Pb_0.91La_0.09(Zr_xTi_1−x)_0.9775O₃ PLZT ceramics, where x =0.70, 0.65 and 0.60, were prepared by a solid-state mixed-oxide technique. Structural information was investigated by X-ray diffraction method. Electric field induced polarization and strain behavior of the PLZT ceramics under an influence of static magnetic field were measured by a Sawyer-Tower circuit in conjunction with Michelson interferometer at various static magnetic fields (0–30.7 mT). The results showed that the imposed magnetic field affected the polarization and induced strain behaviors in PLZT ceramics More interestingly, the imposed magnetic field showed more significant influence on the PLZT ceramic composition near morphotropic phase boundary (MPB), i.e. PLZT 9/65/35. The spontaneous polarization of 180° domain switching was seen to be suppressed by the applied magnetic field.