Quantitative phase microscopy of biological samples using a portable interferometer

This Letter presents the τ interferometer, a portable and inexpensive device for obtaining spatial interferograms of microscopic biological samples without the strict stability and the highly coherent illumination that are usually required for interferometric microscopy setups. The device is built using off-the-shelf optical elements and can easily operate with low-coherence illumination, while being positioned in the output of a conventional inverted microscope. The interferograms are processed into the quantitative amplitude and phase profiles of the sample. Based on the phase profile, the optical-path-delay profile is obtained with temporal stability of 0.18 nm and spatial stability of 0.42 nm. Further experimental demonstration of using the τ interferometer for imaging the quantitative thickness profile of a live red blood cell is provided.     

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.     

Lensless Fourier holography for digital holographic interferometry on biological samples

Digital holography as a tool for highly sensitive, interferometric non-destructive testing has several advantages compared to holographic measurements based on conventional storage media like an all-digital processing and a direct access to the phase of the object wave. Experimental results of interferometric investigations of heart valve bio-prostheses with a setup for lensless Fourier holography are presented which demonstrate that this technique is applicable to such biological samples with their wet and unstable surfaces. Limitations on size and resolution of the reconstructed object caused by the properties of the CCD sensor are discussed.     

基于二次成像的像面干涉高光谱成像方法

像面干涉高光谱成像技术主要应用于遥感成像领域,为了实现不同距离目标的光谱成像探测,提出了一种基于二次成像的像面干涉高光谱成像方法。通过在无限远成像系统中加入前端成像物镜、中继准直物镜和横向剪切分束器,构建一个二次成像的干涉系统。通过采用分离式的前端成像物镜方案,选用变焦镜头或不同焦距的定焦镜头,有效地兼顾远、近距离目标的成像光谱探测。对该方法的成像系统、光谱分辨率和推扫方式等方面进行了分析,进一步搭建了实验装置,对室内近场目标和室外远场目标进行了成像实验,并对生物组织进行了显微光谱干涉成像实验。实验结果表明,该成像方法能够有效用于不同距离目标的高光谱成像探测。     

Spectral interferometry and reflectometry used to measure thin films

A new method for a precise measurement of the oscillatory part of phase change on reflection (interferometric phase) from a thin-film structure is presented. The method, which is based on phase retrieval from the spectral interferograms recorded at the output of a slightly dispersive Michelson interferometer, is combined with reflectometry. The interferometric phase of the thin-film structure is measured precisely using a reference sample of known phase change on reflection. The spectral reflectance of the thin-film structure is also measured in the interferometer. The feasibility of the method is confirmed in processing the experimental data for SiO₂ thin film on a silicon wafer of known optical constants. Four samples of the thin film are used and their thicknesses are determined. We confirm very good agreement between the thicknesses obtained from the interferometric phase and reflectance measurements. PACS  07.60.Ly; 68.55.Jk; 78.20.Bh     

Imaging voltage-dependent cell motions with heterodyne Mach-Zehnder phase microscopy

We describe a heterodyne Mach-Zehnder interferometric microscope capable of quantitative phase imaging of biological samples with subnanometer sensitivity and frame rates up to 10 kHz. We use the microscope to image cultured neurons and measure nanometer-scale voltage-dependent motions in cells expressing the membrane motor protein prestin.     

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。     

Derivative method for phase retrieval in off-axis quantitative phase imaging

We present a method for phase retrieval in off-axis interferometric systems. By numerically calculating the transverse 1st and 2nd order derivatives of the interferogram, we show that one can directly retrieve the quantitative phase image, without the need for Fourier or Hilbert transformations. Because of this, the method is significantly faster than the current approaches. We illustrate our method using biological specimen data from three different off-axis quantitative phase imaging techniques.     

利用白光干涉技术测量块状材料的群折射率

对群折射率的精确而快速测量是光学工程领域一个基础而又亟需解决的难题,本文提出了一套光谱型迈克尔逊白光干涉系统的解决方案.该系统充分利用了微型光纤光谱仪一次测量便可获得所有干涉信息的特点,无需机械扫描装置,具有结构简单和测量快速的优点.与传统的窗口傅里叶变换算法相比,本文采用小波变换直接从干涉信号的小波脊中提取群延迟,减小了由相位求导得到群延迟过程中引入的误差放大效应,进而提高了群折射率的测量精度.基于此迈克尔逊白光干涉系统,在不同干涉位置处对两块不同厚度的石英和BK7玻璃进行了测量,实验结果表明此方法在宽 关键词： 白光干涉 群折射率 小波变换 傅里叶变换     

Trimodal imaging system capable of quantitative phase imaging without 2 pi ambiguities

A neoteric approach to interferometric phase imaging unencumbered by 2 pi phase ambiguities is presented. This technique utilizes an actively controlled angular displacement glass plate positioned in the reference arm of an environmentally stabilized pseudoheterodyne Mach-Zehnder interferometer. The plate is continually adjusted to maintain a constant interferometric output phase, as a phase object in the sample arm is raster scanned. Using a 632.8 nm source, unwrapped phase images of translucent samples ranging from approximately 150 nm to 1.5 microm thick were obtained. This system is incorporated into a conventional near-field scanning optical microscope, which permits simultaneous phase, intensity, and surface morphology studies.     

基于相位展开及拼接算法的一种高精度大量程宽光谱干涉显微术

宽光谱干涉显微术广泛应用于高精密检测领域,它测量样品形貌通常采用垂直扫描干涉术对亚微米至毫米级特征进行测量,以及相移干涉术对纳米级特征进行测量。其中,相移干涉术精度可达纳米级,但量程有限,高度变化对应的相位需限制在区间内。采用包裹相位展开算法可以扩展相移干涉术的量程,也仅适用于平滑表面,当高度起伏超出焦深或者光源相干长度的限定范围时,干涉条纹模糊或对比度丧失,所解算的结果将产生较大误差甚至错误。提出一种基于相位展开及拼接算法的高精度、大量程宽光谱干涉显微测量方法,以干涉条纹调制度量化条纹质量,条纹对比度高、成像清晰的区域对应调制度较高,定义当前焦面条纹调制度高于阈值的区域为理想区域,定义焦面条纹调制度低于阈值的区域为问题区域。以相位展开算法获得理想区域中的样品相位分布,问题区域的包裹相位不进行展开。使用微位移结构纵向移动物镜焦平面,选择合理的步长,使相邻焦面位置理想区域展开后的真实相位保持部分区域重合,根据重合区域的相位值均差可以实现不同焦面位置的高精度相位拼接,最终获得扩展量程的高精度真实相位结果,进而可以恢复样品完整的表面形貌分布。该算法通过对理想区域的筛选,避免了相位在问题区域展...     

Ex vivo characterization of sub-10-fs pulses

An all-mirror dispersion-compensation setup is used to correct for quadratic and cubic phase distortions induced within a custom nonlinear optical microscope. Mouse tail tendon is used to characterize sub-10-fs pulses by interferometric autocorrelation. This is an ideal method for characterizing dispersion from the optical system, immersion medium, and wet biological sample. The generation of very short autocorrelations demonstrates the ability to compensate for phase distortions within the imaging system and efficient second-harmonic upconversion of the ultrashort pulse spectrum within collagen. Compensated autocorrelation traces are presented for biologically relevant objective lenses.     

用白光相移干涉增大表面形貌可测范围的研究

分析研究了我相移干涉应用于表面形貌测量时表面形貌与干涉图像之间的关系,比较了两种不同光谱分布的光束的白光相移干涉特性。依据白光相移干涉中与干涉光强有关的一些特定参量与表面形貌之间的一一对应关系,提出了一种不直接测量相位、避开相位测量不确定性的新方法。所提方法扩大了可测深度范围,可用于测量面形较陡的连续表面或不连续深结构表面。     

ATIR proximity sensing through an absorbing medium

In this paper we describe a new simple interferometric method for measurement of the thickness of a very thin quivette filled with absorbing liquid. The method is based on the interferometric restoration and analysis of both p- and s-components of the attenuated totally internal reflected (ATIR) field. Two different liquid samples were studied experimentally. The interferometric signal obtained by measurements is compared with the theoretical prediction.     

Differential phase measurements in low-coherence interferometry without 2pi ambiguity

Quantitative phase measurements by low-coherence interferometry and optical coherence tomography are restricted by the well-known 2pi ambiguity to path-length differences smaller than lambda/2 . We present a method that overcomes this ambiguity. Introducing a slight dispersion imbalance between reference and sample arms of the interferometer causes the short and long wavelengths of the source spectrum to separate within the interferometric signal. This causes the phase slope to vary within the signal. The phase-difference function between two adjacent sample beam components is calculated by subtraction of their phase functions obtained from phase-sensitive interferometric signal recording. Because of the dispersive effect, the phase difference varies across the interferometric signal. The slope of that phase difference is proportional to the optical path difference, without 2pi ambiguity.     

Quantitative optical phase microscopy

We present a new method for the extraction of quantitative phase data from microscopic phase samples by use of partially coherent illumination and an ordinary transmission microscope. The technique produces quantitative images of the phase profile of the sample without phase unwrapping. The technique is able to recover phase even in the presence of amplitude modulation, making it significantly more powerful than existing methods of phase microscopy. We demonstrate the technique by providing quantitatively correct phase images of well-characterized test samples and show that the results obtained for more-complex samples correlate with structures observed with Nomarski differential interference contrast techniques.     

Optimum quantum state of light for gravitational-wave interferometry

The laser interferometric gravitational-wave detectors are sensitive to the quantum state of light employed in the dark port of interferometric system. In this paper a general quantum state for the dark input port is assumed. The quantum state of light is expanded versus the Fock states. The quantum noise of interferometric system is computed as a function of the quantum state of light. The variational method and the genetic algorithm are employed to determine the coefficients of the dark input port and the laser input power for the minimization of the quantum noise. Calculation shows that the optimum quantum state for the dark input port is very close to the vacuum squeezed state. For this optimum quantum state the quantum noise and optimum laser power reduces one order of magnitude relative to the conventional interferometer.     

Chromatically dispersed interferometry with wavelet analysis

A new white-light interferometry point sensor utilizing a chromatically dispersed depth detection field is addressed. Monitoring the interference in the optical frequency domain allows for microscopic height detection without the necessity of a mechanical axial scan. The problem of limited dynamic range in previously reported spectral interferometric schemes is solved by forming a high-contrast interference window due to the chromatically dispersed focusing of the detection field. In a proof-of-principle experiment, the position of a reflecting object could be retrieved with a focus of 0.8 NA over an axial range of 30 microm by analyzing the phase of the emerging interference wavelets.     

Simple versatile shearing interferometer suitable for measurements on a microscopic scale

Micro-electromechanical systems (MEMS) behave differently from massive samples. Conventional testing and inspection techniques usually fail at the microscale. Recently there has been an increasing interest in the application of optical techniques for microstructure testing, because they are high-resolution, non-contact, full-field, fast and relatively inexpensive. New interferometric systems, which are suitable for microscopic optical metrology, are of interest for engineering and industrial applications.A modified electronic speckle pattern shearing interferometer (ESPSI) with a very simple shearing device has been designed for metrology applications on the microscale. The shearing device consists of two partially reflective glass plates. The reflection coefficients of the coatings are 0.3 and 0.7, respectively. The distance and the tilt between the two glass plates control the size of the shear. A long working distance microscope objective is attached to the CCD camera to form a field of view variable over several millimetres in width. The suitability of the system for microscopic measurements is demonstrated. The capability of the system for phase shifting is also demonstrated. The results obtained are promising for future applications of the ESPSI system for testing and characterisation of MEMS.     

激光高阶横模的相对相位判定与锁定

本文通过理论计算与数值模拟,提出了不同阶数的高阶模式间相对相位的判定与锁定方法。在像平面对两束光的干涉光斑进行空间取样,计算其干涉光强随相对相位的变化,并在此基础上提出了判定与锁定两束不同阶厄米高斯光束HGmn以及不同阶拉盖尔高斯光束LGpl相对位相的方案,并对厄米高斯光束相位判定与锁定进行了实验验证。