20单元双压电片变形镜对Zernike像差空间拟合能力的实验研究

利用20单元双压电片变形镜和13×13阵列哈特曼波前传感器所构成的闭环自适应光学系统,实验测试了双压电片变形镜对3～20项静态Zernike像差的空间校正能力,并将实验结果与仿真计算结果进行了对比.最后分析了哈特曼传感器与双压电片变形镜之间的对准误差对实验结果的影响.研究表明,除了少数几项外,双压电片变形镜对3～20项Zernike像差的拟合误差都小于0.5,各项Zernike仿真和实验结果之差平均小于0.1.计算表明,与严格对准的理想情况相比,双压电片变形镜对3～20项Zernike像差中大多数项的拟合误差都随着失配程度的增加而增大,对准精度对于高阶像差拟合效果的影响尤其严重.     

Pattern classification by using improved wavelet Compressed Zernike Moments

In this paper, an improved Feature Extraction Method (FEM), which selects discriminative feature sets able to lead to high classification rates in pattern recognition tasks, is presented. The resulted features are the wavelet coefficients of an improved compressed signal, consisting of the Zernike moments amplitudes. By applying a straightforward methodology, it is aimed to construct optimal feature vectors in the sense of vector dimensionality and information content for classification purposes. The resulting surrogate feature vector is of lower dimensionality than the original Zernike moment feature vector and thus more appropriate for pattern recognition tasks.Appropriate validation tests have been arranged, in order to investigate the performance of the proposed algorithm by measuring the discriminative power of the new feature vectors despite the information loss.     

A parametrisation of the direct correlation function for the square-shoulder fluid

We introduce a parametrisation of the direct correlation function for the square-shoulder fluid and demonstrate that this parametrisation is in quantitative agreement with the numerical solution of the Ornstein–Zernike equation within the Percus–Yevick approximation. Moreover, the radial distribution function obtained from the parametrisation reproduces quantitatively Monte Carlo simulation data. Our results show that the parametrisation is accurate over a large regime of densities for different interaction ranges and potential strengths.     

腔内像散扰动对正支共焦腔模式影响的数值分析

 针对激光器出光过程中腔内像差扰动带来的输出光束质量和光束能量下降问题,分析了腔内像差扰动对非稳腔模式的影响,并采用数值迭代法计算了理想情形和腔内像散扰动对无源正支共焦腔输出模式强度和相位分布的影响,进一步采用Zernike模式法对光束相位进行了像差拟合,得到了前35阶Zernike像差系数、点扩散函数(PSF)分布和环围能量曲线,计算了腔内像散扰动量与远场Strehl比的关系。结果表明：对小菲涅耳数正支共焦腔,腔内像散扰动对输出光束强度和相位分布均有明显影响,相位分布中一些高阶Zernike像差也有所增大。因此在进行腔内像差校正时,应优先考虑此类像差的校正。     

Zernike多项式拟合干涉面方法研究

本文就专著和文献中关于Zernike多项式拟合干涉波面几乎都建设采用Gram-Schimdt正交化方法,而不采用比较简单的传统经典的最小二乘法问题进行了深入研究,从理论和实践上严格地证明了两种方法的等价性。实践中发现,用最小二乘法求解Zernike多项式拟合系数的速度比用Gram-Schimdt正交化方法提高了三倍之多。由于在精密光测技术中,Zernike多项式已被广泛采用,因此,“等价性”的证明具有重要意义,并对于其它类似问题也有着普遍的参考价值。     

Elemental x-ray imaging using Zernike phase contrast

We develop an element-specific x-ray microscopy method by using Zernike phase contrast imaging near absorption edges, where a real part of refractive index changes abruptly. In this method two phase contrast images are subtracted to obtain the target element: one is at the absorption edge of the target element and the other is near the absorption edge. The x-ray exposure required by this method is expected to be significantly lower than that of conventional absorption-based x-ray elemental imaging methods. Numerical calculations confirm the advantages of this highly efficient imaging method.     

不同对比度下自适应的自动调焦新算法

针对大多数自动调焦函数不能克服对比度变化引起的调焦曲线失去理想特性、陷入局部极小值甚至失去单峰性等问题,介绍了Zernike正交矩,分析了各阶Zernike矩的调焦函数曲线并且提出了一种新的基于Zernike正交矩的自动调焦算法,定义了此算法的公式.与几种常用自动调焦函数在不同对比度条件下进行了调焦效果的比较分析,验证了通过调整各阶Zernike矩的权重系数、可以灵活变换调焦公式,能够适应不同对比度下的调焦过程.实验比较了基于Zernike正交矩的自动调焦算法应用于完全对称型物体和非对称型物体时焦效果的差别,证明了该算法应用于圆形或球状等完全对称型的物体时调焦效果较好.     

Quantitative phase retrieval in X‐ray Zernike phase contrast microscopy

In recent years, increasing attention has been devoted to X‐ray phase contrast imaging, since it can provide high‐contrast images by using phase variations. Among the different existing techniques, Zernike phase contrast microscopy is one of the most popular phase‐sensitive techniques for investigating the fine structure of the sample at high spatial resolution. In X‐ray Zernike phase contrast microscopy, the image contrast is indeed a mixture of absorption and phase contrast. Therefore, this technique just provides qualitative information on the object, which makes the interpretation of the image difficult. In this contribution, an approach is proposed for quantitative phase retrieval in X‐ray Zernike phase contrast microscopy. By shifting the phase of the direct light by π/2 and 3π/2, two images of the same object are measured successively. The phase information of the object can then be quantitatively retrieved by a proper combination of the measured images. Numerical experiments were carried out and the results confirmed the feasibility of the proposed method. It is expected that the proposed method will find widespread applications in biology, materials science and so on.     

Zernike模式像差共轭组合模型

根据Zernike模式在单位圆的同心孔径圆域内某些模式间具有一定耦合性的结论及对应Zernike模式像差在一定同心光瞳区域内的相互抵消特性,对具有相同角频率不同阶数的Zernike模式建立组合模型,同时根据同心光瞳区域内像差均方根值的降幅比参数给出了同心光瞳直径为4mm时的Zernike模式线性共轭组合模型。最后通过共轭组合模型对光学质量影响的研究发现,共轭模型组合之后能显著提高光学质量。同时也表明Zernike模式组合对光学质量的影响不具备叠加性,而对共轭组合模型表现为补偿关系。     

ICF微靶装配体图像清晰度评价方法

现有图像清晰度评价函数在对ICF微靶装配体图像的评价过程中,由于不同零件图像对比度的变化,评价函数极易失去其理想曲线特性,导致聚焦精度降低甚至调焦过程失败。针对这一问题,在分析离焦图像模糊原因的基础上,得出离焦图像究其本质为图像结构变化失真。利用Zernike矩具有描述图像结构特征这一特性,提出一种新的针对微靶装配体图像的清晰度评价函数。评价函数由图像不同阶Zernike矩的线性组合构成,通过调节权重系数来实现微靶装配体不同零件图像的清晰度评价。实验结果表明:相较于现有的评价函数,新的评价函数在对微靶装配体图像评价过程中保持了函数的理想曲线特性,尤其是针对低对比度图像,其在灵敏度和抗噪性方面具有明显优势。