Surface plasmon interferometric microscopy for three-dimensional imaging of dynamic processes

A method, which we named surface plasmon interferometric microscopy, for real-time displaying of the dynamic evolution of the refractive index (RI) of a sample in three-dimensions is demonstrated experimentally. The Fourier fringe analysis technique is employed to get the phase variations of the samples by demodulating the interference patterns captured by a CCD camera, and the 3D RI distribution can be obtained through numerical interpolation from the relation between the phase and the RI of the samples. Our method may provide an interesting way to monitor fast dynamics of physical, biological, and chemical processes in real time.     

Phase aberration compensation of digital holographic microscopy based on least squares surface fitting

Digital holographic microscopy allows the numerical reconstruction of the complex wavefront of samples, especially biological samples such as living cells. In digital holographic microscopy, a microscope objective is introduced to improve the transverse resolution of the sample; however a phase aberration in the object wavefront is also brought along, which will affect the phase distribution of the reconstructed image. We propose here a numerical method to compensate for the phase aberration of thin transparent objects with a single hologram. The least squares surface fitting with points number less than the matrix of the original hologram is performed on the unwrapped phase distribution to remove the unwanted wavefront curvature. The proposed method is demonstrated with the samples of the cicada wings and epidermal cells of garlic, and the experimental results are consistent with that of the double exposure method.     

数字全息显微术中重建物场波前的相位校正

数字全息显微术克服了传统光学显微术无法直接提取样品相位信息的缺点,可以对活体细胞组织等相位型生物样品进行定量测量和有效观察。但在数字全息显微成像过程中,像场弯曲会对再现像相位分布的测量和观察产生影响。提出一种采用相位相减来校正数字全息再现像像场弯曲的方法。通过在样品加入前后两次拍摄全息图,并对数值重建像分别进行去包裹运算再令其相减,即可实现对像场弯曲的有效校正,对蝉翼和大蒜表皮细胞等相位型物体进行测量,并采用数值校正和相位相减两种方法对像场弯曲进行校正。与现有的数值校正方法相比,利用相位相减获得样品三维相位信息的方法更为简单、可靠,是校正像数字全息再现场弯曲的有效方法。     

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1.3 μm.     

Extended depth of focus in tomographic phase microscopy using a propagation algorithm

Tomographic phase microscopy is a laser interferometry technique in which a 3D refractive index map of a biological sample is constructed from quantitative phase images collected at a set of illumination angles. Although the resulting tomographic images provide valuable information, their resolution declines at axial distances beyond about 1 microm from the focal plane. We describe an improved 3D reconstruction algorithm in which the field at the focal plane is numerically propagated to depths throughout the sample. Diffraction is thus incorporated, extending the depth of focus to more than 10 mum. Tomograms with improved focal depth are demonstrated for single HT29 cells.     

Optical near-field distribution in an asymmetrically illuminated tip–sample system for laser/STM nanopatterning

In surface nano-patterning using an atomic force microscope (AFM) tip in scanning tunnelling microscopy (STM) mode and illuminated by a laser, two controversial physical mechanisms exist in the literature: the field-enhancement (FE) model and the thermal-induced mechanical contact (TMC) model. Due to the presence of evanescent waves in the optical near-field, the exact calculation of the field distribution of the tip–sample system in micro/nano scales becomes complicated. There is a lack of understanding of the asymmetrically illuminated tip–sample system. In this paper, full 3D finite-difference time-domain (FDTD) analysis was carried out to investigate the field distribution in different tip–sample systems. The effects of different tip/sample materials (either dielectric or plasmonic material), the gap distance, and laser incidence angles on the field distribution/enhancement have been studied. For the first time, we have demonstrated two new effects which are helpful in distinguishing the controversial mechanisms: (1) on the sample surface, the field peak position has a shift away from the tip-axis at large angles of incidence, and (2) the field enhancement could depend strongly on the horizontal component (perpendicular to tip-axis) of the incident wave instead of the vertical component (along tip-axis). The optimal incident angle is around 30° for the maximum field under the tip. The existence of field-distribution nodes on the 3D tip surface that leads to the in-homogenous heating of the tip is also predicted. PACS 81.16.Mk; 61.80.Ba; 81.16.Rf; 81.65.Cf     

一种微米级高度台阶镜面条纹反射的三维测量系统

提出了一种检测微米级高度衍射台阶结构的条纹反射三维检测方法.对条纹反射光路的理论分析表明,合理选择入射光线角度和液晶屏放置角度以及液晶屏像素尺寸等系统参数,条纹反射系统能够分辨微米乃至亚微米级的镜面台阶.实际构建了一套微米级台阶镜面条纹反射测量实验装置;采用四步相移法进行条纹相位解算,运用移动屏幕方法确定反射光线方程,结合三角交汇原理,对待测台阶镜面进行三维重构.实际测量了名义值为5μm和10μm的台阶镜面,测量结果不确定度在0.5μm内,和商业仪器测量结果的偏差<0.5μm,证明了设计方法的可行性.本文结果对于包含衍射台阶结构的光学元件三维测量研究具有一定的借鉴意义.     

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0.8 μm.     

Near-field penetrating optical microscopy: a live cell nanoscale refractive index measurement technique for quantification of internal macromolecular density

Quantification of intracellular nanoscale macromolecular density distribution is a fundamental aspect to understanding cellular processes. We report a near-field penetrating optical microscopy (NPOM) technique to directly probe the internal nanoscale macromolecular density of biological cells through quantification of intracellular refractive index (RI). NPOM inserts a tapered optical fiber probe to successive depths into an illuminated sample. A 50 nm diameter probe tip collects signal that exhibits a linear relationship with the sample RI at a spatial resolution of approximately 50 nm for biologically relevant measurements, one order of magnitude finer than the Abbe diffraction limit. Live and fixed cell data illustrate the mechanical ability of a 50 nm probe to penetrate biological samples.     

基于谱域相位分辨光学相干层析的纳米级表面形貌成像

提出了一种基于谱域相位分辨光学相干层析的纳米级表面形貌成像方法,由干涉光谱计算样品相邻两点的相位差,得到样品表面相位差分图,经过积分,重建样品表面形貌的定量分布.当相邻两点相位差的绝对值小于π,不产生相位包裹,避免了目前的干涉法相位解包裹存在的问题,将干涉法相邻两点相位差绝对值的限制条件由目前的π扩大到2π,提高了干涉法表面形貌成像的适用范围.参考面和样品置于同一平台之上,消除环境干扰及系统振动的影响,噪声幅度小于0.3 nm.通过对光学分辨率片及表面粗糙度标准样板的表面形貌成像,对本方法进行了验证,系统的轴向分辨率优于1 nm.     

20GeS2·80Sb2S3硫系玻璃的析晶行为及动力学机理研究

实现玻璃微晶化过程控制的基础是要充分认识其析晶行为及动力学机理. 利用示差扫描量热法和析晶热处理等手段, 研究发现 20GeS₂·80Sb₂S₃硫系玻璃属于表面析晶, 在268℃(T_g+30℃)下热处理60 h, 可以获得表面约40 μm的Sb₂S₃晶层复合玻璃陶瓷样品. 在此基础上, 利用非等温法从理论上分析该玻璃的析晶动力学机理. 计算得到其析晶活化能E_c为(223.6±24.1)kJ·mol^-1, 在热处理温度(268℃)下的析晶速率常数K为1.23×10^-4 s^-1, 属于较难析晶的玻璃组成; 玻璃的晶体生长指数m和晶体生长维数n均为2, 表明其Sb₂S₃相的析晶行为是二维生长过程, 与析晶实验结果完全相符. 由此可知, 对于Sb₂S₃晶体复合的硫系玻璃陶瓷样品可通过玻璃粉末压片烧结、带铸法或丝网印刷法制备获得, 为今后功能硫系玻璃的开发提供实验依据和理论指导. 关键词： 硫系玻璃 微晶化 析晶动力学 析晶行为     

飞秒激光湿法刻蚀微纳制造

飞秒激光微加工作为一种新型微纳制造技术,在复杂三维构型制作方面具有其独特的优势,但激光加工效率问题严重制约了飞秒激光微加工技术走向实际工程应用,提出一种飞秒激光湿法刻蚀微纳制造方法,以提高飞秒激光微加工的效率为突破口,通过调控激光与物质相互作用获得材料的目标靶向改性,进而结合化学湿法刻蚀实现硬质材料上的高效和高精度三维微加工,采用这一方法制作出的微透镜尺寸为80 m,球冠高6.7 m,表面粗糙度小于10 nm。利用这种方法,实现了不同结构与特性的高质量微透镜阵列的超精密制备,在石英内部也实现了螺旋微通道的复杂三维结构,螺旋通道直径为20 m,长径比超过100。     

磁阱中超冷玻色气体临界行为的观测

超冷玻色气体为研究量子临界现象提供了一个非常干净的实验系统. 弱相互作用下的三维玻色气体的临界行为与⁴He发生超流相变时的临界行为类似, 都属于三维XY型普适类. 从正常流体到超流的量子相变过程中, 系统会经历一个从无序相到长程有序相的转变; 而在相变点附近, 系统参量会表现出一些奇点的特征. 本文从实验上观测到了静磁阱中超冷⁸⁷Rb玻色气体在凝聚体相变温度T_c附近的临界行为. 原子气体从静磁阱中释放, 经过30 ms的自由飞行后, 通过吸收成像得到原子气体的动量分布; 然后从中扣除热原子气体的动量分布, 提取出空间上处于临界区域内的原子气体动量分布, 并对不同温度下的动量分布半高宽进行统计. 统计结果显示: 在非常接近相变温度T_c时, 动量分布的半高宽突然减小, 表现出十分明显的奇点行为.     

基于单一分光棱镜干涉仪的双通路定量相位显微术

仅仅使用一个单独的分光棱镜(BS),实现了一种用于生物细胞三维成像的双通路定量相位显微术.不同于传统的使用方法,将BS倾斜放置,使中央半反射层与入射光光轴之间存在一个非常小的角度.这样基于BS的分光特性,经过BS后的透射光束和反射光束将会叠加在一起并形成干涉.调节样品位置,利用相机拍摄同时获得了存在π相移的双通路干涉图.这种离轴干涉模式,只需要记录单幅干涉图就可以获得真实的相位信息,方法结构简单,易于操作,适用于微小透明样品的三维形貌测量.     

3D homogeneity study in PMMA layers using a Fourier domain OCT system

Micro-metallic particles embedded in polymers are now widely used in several industrial applications in order to modify the mechanical properties of the bulk. A uniform distribution of these particles inside the polymers is highly desired for instance, when a biological backscattering is simulated or a bio-framework is designed. A 3D Fourier domain optical coherence tomography system to detect the polymer's internal homogeneity is proposed. This optical system has a 2D camera sensor array that records a fringe pattern used to reconstruct with a single shot the tomographic image of the sample. The system gathers the full 3D tomographic and optical phase information during a controlled deformation by means of a motion linear stage. This stage avoids the use of expensive tilting stages, which in addition are commonly controlled by piezo drivers. As proof of principle, a series of different deformations were proposed to detect the uniform or non-uniform internal deposition of copper micro particles. The results are presented as images coming from the 3D tomographic micro reconstruction of the samples, and the 3D optical phase information that identifies the in-homogeneity regions within the Poly methyl methacrylate (PMMA) volume.     

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.     

激光干涉结晶技术制备二维有序分布纳米硅阵列

利用结合移相光栅掩模 (PSGM) 的激光结晶技术在超薄a-SiN_x/a-Si:H/ a-SiN _x三明治结构样品中制备出二维有序分布的纳米硅阵列.原始样品是用等离子体 增强化学气相淀积法生长.a-Si:H层厚为10nm，a-SiN_x 为50nm，衬底材料为SiO ₂/Si或 熔凝石英.原子力显微镜、剖面透射电子显微镜、高分辨透射电子显微镜对样品表面形貌和 微结构的观测结果表明，采用该方法可以在原始淀积的a-Si:H层中得到位置可控的晶化区域 ：每个晶化区域直径约250nm，具有同PSGM一致的2μm周期；晶化区域内形成的纳米硅 颗粒尺寸接近原始淀积的a-Si:H层厚，且晶粒的择优取向为<111>. 关键词： 纳米硅 激光结晶 定域晶化 移相光栅     

Compact,common path quantitative phase microscopic techniques for imaging cell dynamics

Microscopy using visible electromagnetic radiation can be used to investigate living cells in various environments. But bright field microscopy only provides two-dimensional (2D) intensity distribution at a single object plane. One of the ways to retrieve object height/thickness information is to employ quantitative phase microscopic (QPM) techniques. Interferometric QPM techniques are widely used for this. Digital holographic microscopy (DHM) is one of the state-of-the-art methods for quantitative three-dimensional (3D) imaging. Usually it is implemented in two-beam geometry, which is prone to mechanical vibrations. But to study dynamics of objects like red blood cells, one needs temporal stability much better than the fluctuations of the object, which the two-beam geometry fails to deliver. One way to overcome this hurdle is to use self-referencing techniques, in which a portion of the object beam will act as the reference beam. Here the development of self-referencing QPM techniques is described along with the results.     

数值分析在不同偏振时复杂样品的近场强度分布

采用三维时域有限差分法(FDTD),模拟计算了光子扫描隧道显微镜(PSTM)系统中的介质和银质金属样品在不同偏振模式光源下的近场强度分布。使用介质小样品检验探针性能,在探针不同位置计算得到了相似的近场强度分布图,说明编写的程序是可信的。给出了等高扫描时p偏振和s偏振条件下,“PSTM”字样介质样品和银质金属样品上方5nm处的近场强度分布图,结果显示:对介质样品,p偏振波能较好的反映样品的形貌,这是由入射电场的方向决定的;银质金属有表面增强作用,对不同偏振波均能在某种程度上反映样品的形貌,仍有待近一步的研究。     

基于电子束剪切干涉的PIE成像技术研究

提出了基于M?llenstedt电子双棱镜的电压扫描剪切干涉全场ptychographic iterative engine(PIE)显微成像技术.从低到高逐步改变电子双棱镜的电压,并同时记录所形成的剪切干涉条纹,待测样品透射电子束的强度和相位分布就可以用PIE算法得以快速重建,而且双棱镜的方向、位置和实际电场强度分布等诸多实验中不可避免地偏差都可以在迭代过程中自动得以更正.所提技术能够克服现阶段用电子束进行PIE成像的诸多技术困扰,从而有望推动PIE技术在电子显微成像领域的发展和应用.