Non-isoplanatic lens aberration correction in dark-field digital holographic microscopy for semiconductor metrology

In the semiconductor industry,the demand for more precise and accurate overlay metrology tools has increased because of the continued shrinking of feature sizes in integrated circuits.To achieve the required sub-nanometre precision,the current technology for overlay metrology has become complex and is reaching its limits.Herein,we present a dark-field digital holographic microscope using a simple two-element imaging lens with a high numerical aperture capable of imaging from the visible to near-infrared regions.This combination of high resolution and wavelength coverage was achieved by combining a simple imaging lens with a fast and accurate correction of non-isoplanatic aberrations.We present experimental results for overlay targets that demonstrate the capability of our computational aberration correction in the visible and near-infrared wavelength regimes.This wide-ranged-wavelength imaging system can advance semiconductor metrology.

Thioacetamide Additive Homogenizing Zn Deposition Revealed by In Situ Digital Holography for Advanced Zn Ion Batteries

Zinc ion batteries are considered as potential energy storage devices due to their advantages of low-cost,high-safety,and high theoretical capacity.However,dendrite growth and chemical corrosion occurring on Zn anode limit their commercialization.These problems can be tackled through the optimization of the electrolyte.However,the screening of electrolyte additives using normal electrochemical methods is time-consuming and labor-intensive.Herein,a fast and simple method based on the digital holography is developed.It can realize the in situ monitoring of electrode/electrolyte interface and provide direct information concerning ion concentration evolution of the diffusion layer.It is effective and time-saving in estimating the homogeneity of the deposition layer and predicting the tendency of dendrite growth,thus able to value the applicability of electrolyte additives.The feasibility of this method is further validated by the forecast and evaluation of thioacetamide additive.Based on systematic characterization,it is proved that the introduction of thioacetamide can not only regulate the interficial ion flux to induce dendrite-free Zn deposition,but also construct adsorption molecule layers to inhibit side reactions of Zn anode.Being easy to operate,capable of in situ observation,and able to endure harsh conditions,digital holography method will be a promising approach for the interfacial investigation of other battery systems.

A novel random phase-shifting digital holographic microscopy method

This paper proposes a new method that reconstructs the information of specimen by using random phase shift step in digital holographic microscopy (DHM). The principles of the method are described and discussed in detail. In practical experiment, because the phase shifter is neither perfectly linear nor calibrated, digital holograms with inaccurate phase shift step are recorded by the charge-coupled device (CCD). The phase could be accurately reconstructed from the recorded digital holograms by using the random phase-shifting algorithm, which makes up for reconstructed phase error caused by ordinary phase-shifting algorithm. The phase aberration compensation is also discussed. In order to verify the flexibility of the proposed method, numerical simulation of random phase-shifting DHM was carried out. The simulation results illustrated that the presented method is effective when the phase shift step is unknown or random in DHM.

Resolution enhancement of digital holographic microscopy via synthetic aperture:a review

Digital holographic microscopy(DHM),which combines digital holography with optical microscopy,is a wide field,minimally invasive quantitative phase microscopy(QPM)approach for measuring the 3D shape or the inner structure of transparent and translucent samples.However,limited by diffraction,the spatial resolution of conventional DHM is relatively low and incompatible with a wide field of view(FOV)owing to the spatial bandwidth product(SBP)limit of the imaging systems.During the past decades,many efforts have been made to enhance the spatial resolution of DHM while preserving a large FOV by trading with unused degrees of freedom.Illumination modulation techniques,such as oblique illumination,structured illumination,and speckle illumination,can enhance the resolution by adding more high-frequency information to the recording system.Resolution enhancement is also achieved by extrapolation of a hologram or by synthesizing a larger hologram by scanning the sample,the camera,or inserting a diffraction grating between the sample and the camera.For on-chip DHM,spatial resolution is achieved using pixel super-resolution techniques.In this paper,we review various resolution enhancement approaches in DHM and discuss the advantages and disadvantages of these approaches.It is our hope that this review will contribute to advancements in DHM and its practical applications in many fields.

Antifouling mechanism of natural product-based coatings investigated by digital holographic microscopy

Using natural product-based antifouling coatings has proven to be an effective strategy to combat biofouling.However,their antifouling mechanisms are still unclear.In this study,the antifouling mechanism of natural product-based coatings consisting of bio-sourced poly(lactic acid)-based polyurethane and ecofriendly antifoulant(butenolide)derived from marine bacteria was revealed by observing 3D bacterial motions utilizing a 3D tracking technique-digital holographic microscopy(DHM).As butenolide content increases,the density of planktonic marine bacteria(Pseudomonas sp.)near the surface decreases and thus leads to a reduced adhesion,indicating that butenolide elicits the adaptive response of Pseudomonas sp.to escape from the surface.Meanwhile,among these remained cells,an increased percentage is found to undergo subdiffusive motions compared with the case of smaller dose of butenolide.Further experiments show that butenolide can accelerate their swimming velocity and reduce flick frequency.Antibacterial assay confirms that butenolide-based coating shows high efficacy of antifouling performance against Pseudomonas sp.but without killing them like 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one(DCOIT).

面向微光学元件表面形貌测量的涡旋相移数字全息技术

非接触、无损害的相移数字全息技术对微光学元件检测具有独特优势。因传统的相移数字全息技术需要对相移器进行精细控制和繁琐校准,同时其光路易受到机械振动干扰,导致全息再现像的质量降低。本文借助涡旋光特殊的相位分布,提出了一种基于涡旋相移数字全息的微光学元件表面形貌测量方法。该方法利用螺旋相位板调制涡旋相位,引入高精度相移。基于构建的涡旋相移数字全息显微实验装置,采用干涉极值法确定了相移干涉图之间的真实相移量,并对螺旋相位板的旋转角度与相移量的关系进行标定,实验验证了涡旋相移的可行性;对微透镜阵列进行了重复测量实验,将测试结果与ZYGO白光干涉仪的测试结果进行比较。结果表明:测量得到单个微透镜的平均纵向矢高为12.897μm,平均相对误差为0.155%。所提方法可以实现对被测微光学元件表面形貌的高精度测量,具有易操作、稳定可靠、准确性高等优点。

Multiframe full-field heterodyne digital holographic microscopy

Digital holographic microscopy using multiframe full-field heterodyne technology is discussed in which two acousto-optic modulators are applied to generate low-frequency heterodyne interference and a high-speed cam- era is applied to acquire multiframe full-field holograms. We use a temporal frequency spectrum analysis algo- rithm to extract the object＇s information. The twin-image problem can be solved and the random noise can be significantly suppressed. The relationship between the frame number and the reconstruction accuracy is dis- cussed. The typical objects of microlenses and biology cells are reconstructed well with lO0-frame holograms for illustration.

Integrated self-referencing single shot digital holographic microscope and optical tweezer

Digital holographic microscopy is a single-shot technique for quantitative phase imaging of samples,yielding thickness profiles of phase objects.It provides sample features based on their morphology,leading to their classification and identification.However,observing samples,especially cells,in fluids using holographic microscopes is difficult without immobilizing the object.Optical tweezers can be used for sample immobilization in fluids.The present manuscript provides an overview of our ongoing work on the development of a compact,low-cost microscopy system for digital holographic imaging of optically trapped samples.Integration of digital holographic microscopy system with tweezers is realized by using the optical pickup unit extracted from DVD burners to trap microsamples,which are then holographically imaged using a highly compact self-referencing interferometer along with a low-cost,in-house developed quadrant photodiode,providing morphological and spectral information of trapped particles.The developed integrated module was tested using polystyrene microspheres as well as human erythrocytes.The investigated system offers a multitude of sample features,including physical and mechanical parameters and corner frequency information of the sample.These features were used for sample classification.The proposed technique has vast potential in opening up new avenues for low-cost,digital holographic imaging and analysis of immobilized samples in fluids and their classification.

Perfect digital holographic imaging with high resolutionusing a submillimeter-dimension CCD sensor

In order to improve the resolution of digital holography with a common-dimension charge-coupled device (CCD) sensor, the point spread functions are briefly derived for the commonly used and practical post-magnification, pre-magnification, and image-plane digital holographic microscopic systems. The ultimate resolutions of these systems are analyzed and compared. The results show that the ultimate lateral resolution of pre-magnification digital holography is superior to that of post-magnification digital holography in the same conditions. We also demonstrate that the ultimate lateral resolution of image-plane digital holography has no correlation with the photosensitive dimension of the CCD sensor, and it is not significantly related to the pixel size of the sensor. Moreover, both the ultimate resolution and the imaging quality of image-plane digital holography are superior to that of pre- and post-magnification digital holographic microscopy. High-resolution imaging, whose resolution is close to the ultimate resolution of the microscope objective, can be achieved by image-plane digital holography even with a submillimeter-dimension sensor. This system, by which perfect imaging can be achieved, is optimal for commonly used digital holographic microscopy. Experimental results demonstrate the correctness of the theoretical analysis.

A Preliminary Study on the Evaluation of Human Sperm Head Morphology with a Domestic Digital Holographic Image System

The head of sperm was imaged with domestic digital holographic microscopy(DHM),and then the quantitative three-dimensional size information of normal sperm and teratozoospermic sperm was compared and analyzed.DHM sperm imaging and repeated quantitative evaluation were used to determine the morphology of the sperm head in two patients with teratozoospermia and four volunteers with normal semen parameters.Sixty and 139 sperm of teratozoospermia patients and normal people were photographed by digital hologram,respectively.The differences in head height and width were compared and statistically analyzed.The sperm head height of the teratozoospermia group was 3.06±1.66μm,which was significantly lower than that of the normal sperm group(4.54±1.60μm,p<0.01),but there was no significant difference in the head width between the two groups.Compared with the traditional two-dimensional optical microscope observation method,the DHM system can provide three-dimensional quantitative information for the sperm head and thus may help in the comprehensive clinical evaluation of the sperm head structure.

数字全息显微术对细胞的研究

通过数字全息显微的方法分析研究了新鲜洋葱表皮细胞的形貌结构.根据全息理论、光的衍射理论和透镜的相位变换性质,从理论上分析了数字全息显微原理,并依据四步相移和最小二乘去包裹技术,研究了重构细胞相位的方法.分析比较了不同参考光对数字全息显微分辨率的影响,设计了用球面光波作为参考光记录数字全息显微的装置.以新鲜洋葱表皮细胞为样本完成了实验检测和相位重构,得到了细胞的相位和三维信息,并粗略估计了细胞宽度和厚度.系统分辨率达到了1 .3μm.

数字全息显微系统结构参量对再现像质的影响

为了获取高质量的数字全息显微再现像,分析了同轴相移数字全息显微系统结构参量对再现像质的影响.首先经过计算得出理想成像时,像空间物光波频率完全由物体面形结构频率和系统放大倍率决定.然后基于显微成像时物光波的所有频率分量都应该被有效记录的分析,得出在同轴相移系统中放大倍率必须使物光波的空间频率缩小到满足采样要求;并得出在相同的放大倍率下记录距离会影响有效记录的物体尺寸,记录器件离开像平面的距离越小,有效记录的物体尺寸越大,在像平面上时有效记录的物体尺寸最大.计算机仿真和光学实验都证明了上述结论的正确性.

数字全息术用于光学元件表面缺陷形貌测量

利用像面数字全息显微术对光学元件表面缺陷的三维形貌测量进行了理论及实验研究。设计并搭建了相应光路系统记录全息图,采用角谱算法数值重建物光场,通过相位修正消除了系统误差引入的波前畸变,获得了经过待测光学元件表面缺陷调制的物光相位分布,并根据建立的相位分布与表面缺陷面形的关系模型计算得到缺陷三维形貌。实验以多个划痕和麻点等常见表面缺陷作为测量对象,分别获得了它们的三维形貌,以其中一条实际宽度为35μm、深度为270nm的划痕为例,测量得到该划痕的宽度为35.21μm,平均深度为267.6nm,与真实值相比,横向测量误差为0.6%,纵向测量误差为0.9%。实验结果证实该测量方法是有效、可靠的,能够准确测量光学元件表面缺陷的三维形貌,因而有助于判断光学元件损伤程度以及分析缺陷对系统波前的影响,对保障高功率激光装置的安全正常运行有重要意义。

无透镜片上显微成像技术:理论、发展与应用

同时实现大视场、高分辨率成像是光学显微技术发展至今不断追求的永恒目标。传统光学显微镜由于其光学设计原理限制,空间带宽积一般总是限制在百万像素量级,从而无法同时兼顾高分辨率与大视场。另一方面,复杂的光学系统也使显微镜变得日趋昂贵、笨重、复杂且难以维护,极大地限制了其推广和应用。无透镜片上显微成像技术是近年来发展出的一种新概念计算成像技术:其不利用成像透镜聚焦,而直接将所观测的样本紧贴于成像器件光敏面上方记录图像,并结合相应的图像恢复算法实现清晰物像的反演与重构。由于具有视野大、分辨率高、无需标记、成本低、便携性好和可实现三维(3D)成像等优点,无透镜片上显微镜有望拓展传统显微成像技术的疆界,成为一种新型的快捷、便携的就地检验(POCT)工具。文中从无透镜成像基本原理、实验系统、重构方法及其典型应用进行了综述。最后,讨论了无透镜显微成像现存的一些关键问题以及今后可能的发展方向。

反射式数字全息显微术对细胞的研究

根据全息理论和光的衍射理论,理论分析了数字全息显微术原理,并依据四步相移和最小二乘相位展开技术,研究了重构细胞相位的方法.设计了用球面光波作为参考光的反射式数字全息显微光路,通过反射式数字全息显微术的方法分析研究了新鲜洋葱表皮细胞的形貌结构.实验以新鲜洋葱表皮细胞为样本,完成了实验检测和相位重构,得到了细胞的相位和三维信息.分析表明,系统理论分辨率应达到0.8μm.

预放大离轴菲涅耳数字全息显微技术

预放大离轴全息方法引入了高数值孔径显微物镜,放大了物体的精细结构,使得全息图的信息量更容易与CCD的抽样能力相匹配,与同轴全息显微技术相比,只需拍摄一张全息图,操作简单,具有良好的应用价值。依据全息理论和菲涅耳衍射理论,推导出预放大离轴菲涅耳全息显微系统中CCD记录面的二维光波信息。设计了采用平面光波作为参考光的透射式数字全息显微系统,并对系统分辨率进行了分析。利用该系统对新鲜的洋葱细胞样本和百合的茎细胞样本进行了实验研究,得到了其高分辨率的再现像。

欠采样包裹相位图的展开算法

利用四种常见算法对由球面参考光像面数字全息显微术得到的中药饮片海金沙细胞的包裹相位图进行了相位解包裹。结果表明:基于离散余弦的最小二乘算法和预条件共轭梯度算法会使欠采样区域的误差进行传递,使得解包裹相位产生较大误差;质量图导向路径跟踪算法由于未识别残差点,导致出现"拉线"或者"孤岛"区域,而且处理速度很慢;基于横向剪切干涉的最小二乘算法处理欠采样包裹相位图的效果最好,而且处理速度较快。

用于微结构几何量测量的数字全息方法

基于光学全息和数字图像处理技术发展起来的数字全息方法,其显著的优越性表现在全视场、无损、非接触,且能得到高分辨率。无透镜傅里叶变换数字全息,最能充分利用CCD的有限带宽,而且允许的最小的记录距离与被记录物体的大小成正比,对于微小物体可以达到很高的分辨率,因此广泛用于微结构几何量的测量。然而,其记录距离受到光学元件物理尺寸的限制,分辨率不能得到很好地提高。应用预放大离轴菲涅耳数字全息,能够更大程度地提高分辨率,达到1m以下的横向分辨率。

基于数字全息显微的海洋浮游生物三维形貌快速重建方法研究

针对海洋浮游生物实时探测中,三维形貌特征难以快速获取的问题,本文提出了一种海洋浮游生物三维形貌快速重建的方法。基于离轴菲涅尔数字全息显微系统,通过改进相位恢复方法预消除相位畸变,直接得到正确的相位信息,进而对浮游生物三维形貌重建。该方法不需要进行后期复杂的相位补偿计算,就可以对浮游生物三维形貌进行快速重建,有利于对动态、微小尺寸的浮游生物进行实时探测及分析。论文对青岛近海岸浮游生物桡足类和夜光虫进行了三维形貌重建,分辨率可达到3.5μm。实验结果为离轴菲涅尔数字全息显微系统用于海洋浮游生物原位、实时探测的可行性提供了依据。

结合划线拟合和深度学习的数字全息显微相位像差自动补偿方法

针对动态观察活体细胞形态的数字全息显微应用,提出了一种结合划线拟合和深度学习的自动相位像差补偿方法.首先在全息面提取中心十字线上的物光场相位值,通过二次多项式数值拟合构建相位掩模完成相位像差初步补偿.然后在成像面运用卷积神经网络生成二值化图像掩膜,提取物光场中无物体区域的相位值,再次通过高阶多项式进行数字拟合构建相位掩模完成相位像差精确补偿.最后得到无相位像差的再现相位像.该方法通过在全息面划线取值和数字拟合有效补偿物光中的主要相位像差,降低了成像面物光场的图像轮廓复杂性,利用有限的训练数据集获得能够准确建立图像分割的深度学习模型,从而实现了准确的无需人工干预的数字全息显微自动相位像差补偿.基于离轴数字全息显微成像系统对多种具有不同形态特征的活体细胞开展动态观察实验,并进一步应用该方法进行子宫内膜癌细胞抗药性筛选.结果表明该方法可以很好地用于动态显微观察,从而为生物学细胞动态研究提供实验依据.