Two-exposure quasi-common-path point diffraction interferometric phase microscopy using a four-step algorithm

A two-exposure nearly common-path point diffraction interferometric phase microscopy (IPM) is presented using polarization modulation and one-step grating shifting to implement quantitative phase imaging. The IPM is constructed by an improved Michelson configuration with a reflective grating, and its frequency spectrum generated by a circularly polarized object beam makes double copies through a beam splitter. One copy is low-pass filtered and reflected by a reflective pinhole mirror to create a reference beam, and the other copy is converted by a polarizer and then reflected by a reflective grating to achieve a 45° linearly polarized object beam. By the combination of a polarizing cube beam splitter with 45° tilted angle and a translation of the reflective grating with a π phase shift, four interferograms with π/2 phase shift can be obtained in two exposures. The standard four-step algorithm can then be used to reconstruct the phase of the specimen. The utility of the proposed method was demonstrated with measurements on a phase plate, cells and an oil drop.     

Interferometric phase microscopy using slightly-off-axis reflective point diffraction interferometer

An interferometric phase microscopy (IPM) is proposed using slightly-off-axis reflective point diffraction interferometry for quantitative phase imaging. A retro-reflector consisting two mirrors is used to generate an angle between the object beam and reference beam, and a 45° tilted polarizing beam splitter is used to split the horizontal and vertical components of the both beams. Two carrier interferograms with π/2 phase-shift can be acquired in one shot, and the phase distribution of a thin specimen can be retrieved using a fast reconstruction method. The new IPM without loss in the utilization of the input-plane field of view combines the real time and optimizing detector bandwidth measurement benefit associated with slightly-off-axis method, high stability associated with common path geometry, and simplicity in terms of procedure and setup. Experiments are carried out on both static and dynamic specimens to demonstrate the validity and stability of the proposed method.     

A reflective surface-relief two-layer grating for splitting beams with the polarization-selective property

A polarization-selective beam splitter is presented based on a reflective surface-relief two-layer grating with a metal slab. The grating is composed of two dielectric layers and a metal slab on the substrate. For TE polarization, efficiencies of 97.58% can be diffracted into the reflective −1st order. For TM polarization, two-port output of 47.55% and 47.11% can be split into the 0th order and the −1st order, respectively. Such a polarization-selective beam splitter can be fulfilled by one grating in reflection. The grating depths of two layers are optimized by using rigorous coupled-wave analysis with the given duty cycle of 0.6 and period of 1100 nm. The performance for different incident conditions is investigated when the incident wavelength and angle deviate from the central wavelength and the Bragg angle, respectively. For TM polarization, good uniformity can still be achieved within the given incident wavelength and angle regions. For TE polarization, the reflective polarization-selective beam splitter can have merits of wideband for different incident wavelengths.     

A mixed metal dielectric sandwiched grating for polarization-selective reflection

A mixed metal dielectric sandwiched grating is described for polarization-selective reflection. The novel grating is composed of substrate, metal slab, two dielectric grating layers, and covering layer. The polarization-selective grating is optimized by using rigorous coupled-wave analysis for the usual duty cycle of 0.5. With the optimized grating parameters, reflective efficiency of 96.49% can be diffracted into the −1st order for TE polarization. And two-port output of 48.26%/48.27% can be diffracted into the 0th and the −1st orders for TM polarization. Polarization-selective reflection with good performance can be obtained by the mixed metal dielectric sandwiched grating. The usual duty cycle of 0.5 makes it easy and simple to be fabricated for practical applications. Moreover, the polarization-selective beam splitter based on the mixed metal dielectric sandwiched grating has advantages of wide incident wavelength range for TE polarization and angular bandwidth for TM polarization.     

Phase-shifting interferometry with four interferograms using linear polarization modulation and a Ronchi grating displaced by only a small unknown amount

A method to reduce the number of captures needed in phase-shifting interferometry is proposed on the basis of grating interferometry and modulation of linear polarization. The case of four interferograms is considered. A common-path interferometer is used with two windows in the object plane and a Ronchi grating as the pupil, thus forming several replicated images of each window over the image plane. The replicated images, under proper matching conditions, superpose in such a way so that they produce interference patterns. Orders 0 and +1 and −1 and 0 form useful patterns to extract the optical phase differences associated to the windows. A phase of π is introduced between these orders using linear polarizing filters placed in the windows and also in the replicated windows, so two π-shifted patterns can be captured in one shot. An unknown translation is then applied to the grating in order to produce another shift in the each pattern. A second and final shot captures these last patterns. The actual grating displacement and the phase shift can be determined according to the method proposed by Kreis before applying proper phase-shifting techniques to finally calculate the phase difference distribution between windows. Related simulations and experimental results are given.     

Phase profile analysis of transparent objects through the use of a two windows interferometer based on a one beam splitter configuration

In this research we implemented a two windows interferometer based on polarization phase shifting and grating interferometry techniques in order to retrieve the phase data profile of the object in a single capture. The optical configuration has two optical beams with circular polarization in opposite directions, and it is coupled with a 4-f system. An amplitude grid is used as a filter which is placed at the Fourier plane to obtain replicas of each beam which can properly interfere, depending on the separation between beams. The interferometer presents the capability of changing the beam separation in order to make different orders interfere properly. The interference patterns produced can be separately modulated through the operation of linear polarizer's placed on each interference replica. In order to present the capabilities of the system we will select four interferograms result of contiguous orders interference.     

The Forked Blazed Grating as a Quasioptical Element for Gyrotron Applications

In previous papers we have shown how beams of millimeter-wavelength electromagnetic radiation with phase singularities can be generated by diffraction from a specially-configured forked blazed grating. Here we consider how the hollow conical beam output of a gyrotron is diffracted by this kind of grating. Two applications are considered; using the grating (a) as a single-element quasioptical antenna to convert the output into a well-collimated gaussian-like beam and (b) as a device to enable the estimation of the fractions in oppositely-rotating modes in the gyrotron output.     

菌紫质同线偏振全息记录时再现光偏振方向对衍射效率的调制

当用相同偏振方向的物光和参考光在菌紫质薄膜上记录光栅时,再现光的偏振方向会影响其衍射效率.采用琼斯矩阵方法对此进行了理论分析,结果显示,再现光的偏振方向对衍射光的光强产生余弦调制;当再现光的偏振方向平行或垂直于记录光的偏振方向时,衍射光仍为线偏振光,其他情况下衍射光均变成椭圆偏振光.再现光偏振方向对衍射效率峰值的调制为正向余弦调制,对衍射效率稳定值的调制为反向余弦调制(与前者在相位上相差π).加入辅助紫光可抑制光栅的饱和,从而使得再现光偏振对衍射效率稳定值的调制由反向余弦调制变为正向余弦调制,并且提高了衍 关键词： 菌紫质 光致各向异性 衍射效率 琼斯矩阵     

基于二维光栅分光的同步移相干涉测量技术

为了干涉测量的抗振目的,提出了一种新的同步移相干涉测量方案并搭建了实验装置。整个测量系统在迈克耳孙偏振移相干涉仪的基础上,利用一个正交的二维光栅产生对称分光,选取对于理想光栅衍射效率一致的(±1,±1)级衍射光作为测量分光路,使之分别通过偏振方向依次相差45°的一个偏振片组,从而分别形成0°、90°、180°和270°相移的四幅移相干涉图,按照传统的四步移相算法,对被测波面进行了复原。分析了光强畸变和移相误差对系统的测量误差的影响。利用该系统测量一球面系统,结果与在ZYGO干涉仪上相比较,球面系统的均方根误差相差0.012λ,峰谷值相差0.051λ。     

超冷原子中的拉曼增益光栅

为提高光栅的衍射效率,提出了基于主动拉曼效应的超冷原子光栅系统。理论研究表明：通过拉曼增益的空间周期性调节,可有效地将沿垂直光栅方向传播的弱探测光衍射到一级方向,同时零级衍射光将被放大。当系统中引进微波场的原子相干效应时,可以进一步提高光栅的一级衍射效率。在一定的条件下,拉曼增益光栅的一级衍射效率可高于电磁诱导相位光栅的一级衍射效率。该系统可作为高效光开关用于全光网络。     

A novel approach to high-sensitivity grating interferometry

The authors propose a new approach for obtaining information about in-plane and out-of-plane displacements of an object tested using high-sensitivity grating interferometry. The interferences of each of the specimen grating diffraction orders with a reference beam are recorded separately. Computer addition and subtraction of the phase functions calculated from the interferograms give the in-plane and out-of-plane displacement values, respectively. The authors present their experimental work, and then compare their results with those obtained using a conventional grating interferometry approach.     

Depth sensing using coherence mapping

A method for depth sensing based on sensing the visibility associated with the coherence function of a laser source is presented. The setup is based on an electronic speckle pattern interferometric (ESPI) setup, where the object depth is encoded into the amplitude of the interference pattern without the need for depth scanning. After performing phase-shifting method, the object three-dimensional (3-D) shape is reconstructed by means as a range image from the visibility of the image set of interferograms and where each gray level represents a given object depth. Experimental results validate the proposed approach for reflective diffuse objects at different measurement distances.     

On-line beam diagnostics based on single-shot beam splitting phase retrieval

We propose a novel on-line beam diagnostic method based on single-shot beam splitting phase retrieval. The incident beam to be measured is diffracted into many replicas by a Dammann grating and then propagates through a weakly scattering phase plate with a known structure; the exiting beams propagate along their original direction and form an array of diffraction patterns on the detector plane. By applying the intensity of diffraction patterns into an iterative algorithm and calculating between the grating plane, weakly scattering plane, and detector plane, the complex field of the incident beam can be reconstructed rapidly; the feasibility of this method is verified experimentally with wavelengths of 1053 and 632.8 nm.     

利用双光栅的多普勒频移测速度

衍射光的多普勒频移是与光栅运动速度有关的量.激光束依次通过动光栅、静光栅衍射,然后使1对光频不同、彼此平行又能部分重叠的衍射光束通过硅光电池进行光电转换,得到的信号电流的频率等于多普勒频移.信号电流经I/V转换、f/V转换和A/D转换后,由单片机测出电压,由此就可以确定动光栅的运动速度.最后对利用双光栅的多普勒频移测气垫导轨上滑块的速度进行分析和讨论.     

Phase singularities of nonparaxial cosh-Gaussian vortex beams diffracted by a rectangular aperture

Analytical expression for the propagation of nonparaxial cosh-Gaussian (ChG) beams diffracted by a rectangular aperture is derived based on the vector Rayleigh-Sommerfeld diffraction integrals and expansion of the aperture window function into a finite sum of complex Gaussian functions, and used to study the phase singularities of nonparaxial diffracted ChG vortex beams. The pair creation, annihilation, motion of phase singularities in the diffracted field and the dependence of position and number of phase singularities on the aperture and beam parameters, as well as on the beam nonparaxiality are illustrated by numerical examples.     

Four wave mixing spectroscopy and additional boundary conditions: A proposal

A nonlinear spectroscopic method for the direct measurement of amplitude ratios among various polariton modes in spatially dispersive media is proposed and theoretically analyzed. In this method four wave mixing among three laser beams is used. Two beams have the same frequency higher than the longitudanal exciton, but different angles of incidence, and excite various polariton modes in the crystal. The third is the probe beam whose frequency can be chosen in the transparent region of the crystal. The probe beam is elastically diffracted from the grating generated by the interference between some appropriate pair of excited modes. The phase matching condition and hence the exit angle of the diffracted beam depend sensitively on the wave-vector of the grating. Thus the contribution from each polariton branch can be measured separately, by selectively tuning the angle of incidence of the probe beam; from the measured ratio the amplitude ratio, and hence the ABC can be obtained.     

Enhancing the phase profile and contrast of an interferogram by polarization recording in bacteriorhodopsin

Interferometry is a technique for reconstructing the profiles of phase objects. We present a novel interferometric setup for generating interferograms with doubled phase profile and enhanced contrast compared with the standard interferogram. The proposed system consists of a two-beam interferometer in which the reference and test waves are circularly polarized orthogonally to each other. They are superposed upon a bacteriorhodopsin film, creating a polarization grating that is distorted by the phase of the test object. This polarization pattern is read by a polarized He-Ne beam. We show analytically and experimentally that, when the zero diffraction order is removed, an interferogram with doubled phase profile and enhanced contrast is obtained.     

Measuring Stokes parameters by means of a polarization grating

Ordinary gratings act on the amplitude and (or) the phase of a wave front. Polarization gratings produce instead a periodic modulation of the state of polarization. A simple grating of the latter type is constituted by a linear polarizer whose orientation varies periodically along a line. It is shown that, for a generic polarization state of the incident field, such a grating gives rise to first-order diffracted beams with counterrotating circular polarizations. It is also shown that such a grating can be used for measuring the Stokes parameters of a light beam in an achromatic manner. Several extensions are briefly discussed.     

An Iteratively-Designed Binary Phase Grating for Flattop Beam Generation

A binary phase grating capable of shaping an incident Gaussian beam to a flattop beam in a Fourier domain is designed iteratively. It is essential in grating design to consider the phases of diffracted waves by the grating, in addition to their amplitude uniformity and diffraction efficiency. The optimized grating phase produces the in-phase diffracted waves that interfere constructively to form a uniform amplitude and phase profile. The dependence of the shaped profile on the illuminating amplitude distribution, the grating misalignment, and the lens focusing error is investigated by computer simulation and optical experiment.     

一种新的光纤光栅温度传感器的设计

提出一种新的光纤温度传感器,在单模光纤的45°倾斜端面上制作光栅。沿光纤光轴传输到光纤倾斜端面上的光将被全反射,同时被光栅衍射。适当选择光栅常数,可以使衍射零级和衍射负1级在经过不同的传播路径后相遇,并产生干涉,干涉条纹的变化将体现传感器所处环境温度的变化。由理论计算知,当工作波长为1.55μm时,这种传感器可测的温度变化范围为1179℃。