Theoretical development and experimental evaluation of imaging models for differential-interference-contrast microscopy.

Imaging models for differential-interference-contrast (DIC) microscopy are presented. Two- and three-dimensional models for DIC imaging under partially coherent illumination were derived and tested by using phantom specimens viewed with several conventional DIC microscopes and quasi-monochromatic light. DIC images recorded with a CCD camera were compared with model predictions that were generated by using theoretical point-spread functions, computer-generated phantoms, and estimated imaging parameters such as bias and shear. Results show quantitative and qualitative agreement between model and data for several imaging conditions.     

Superresolution for digital versatile discs (DVD's)

We discuss an extension of our previous research that uses image-plane optical masks to achieve superresolution in confocal scanning microscopy to the coherent optics of digital versatile disc readers. The theory and the design of superresolving optics for such high-numerical-aperture scanning coherent imaging systems is presented. A superresolving optical reader would permit superdense optical data storage, giving an improvement over the equivalent conventional storage densities by at least a factor of 2.     

A theoretical and experimental study to point out the notion of loading mode in damage mechanics: Application to the identification and validation of a fatigue damage modeling for laminates composites

A model of fatigue-induced intralaminar cracking in strongly anisotropic laminates is presented. The features of the microscopic phenomenon are explicitly taken into account at the macroscopic level by the use of two variables, which define a new concept in Damage Mechanics that results not only in a coherent model of crack density evolution, but also in a coherent treatment of damage deactivation. Damage evolution indeed is strongly dependent on the local loading mode in each ply where cracking occurs. Experiments on complex lay-ups provided sufficient data for complete calibration of the model. These tests also allowed to validate the theoretical choice of the damage variable. Finally, numerous simulations that emphasize the relevance of the approach are presented.     

Plasmon-enhanced second-harmonic generation from ionic self-assembled multilayer films

We have demonstrated large enhancements of the effective second-order nonlinear susceptibility (chi(2)) of ionic self-assembled multilayer (ISAM) films, causing a film with just 3 bilayers to be optically equivalent to a 700-1000 bilayer film. This was accomplished by using nanosphere lithography to deposit silver nanoparticles on the ISAM film, tuning the geometry of the particles to make their plasmonic resonances overlap the frequency of optical excitation. An enhancement in the efficiency of second harmonic generation (SHG) by as much as 1600 times was observed. Even though this is already a large value, we suggest that further refinements of the techniques are expected to lead to additional enhancements of similar or larger magnitude.     

Coherent transfer function of Fourier transform spectral interferometric coherent anti-Stokes Raman scattering microscopy

We analyze the optical resolution of Fourier transform spectral interferometric-coherent anti-Stokes Raman scattering microscopy, which extracts the complex amplitude of an image by using a spectral interferometric effect. Image-formation formulas are presented that describe the properties of the image observed by the apparatus. The image-formation properties represented by the coherent transfer function are different depending on the mode (transmission, reflection, etc.) of the microscopy.     

Imaging theory of nonlinear Raman confocal microscopy

A novel nonlinear Raman confocal microscopy utilizing Raman induced Kerr effect spectroscopy (RIKES) is presented in this paper. The imaging theory of RIKES confocal microscopy with Gaussian beam is derived. The imaging properties of RIKES confocal microscopy and the impact of different beam waist widths of Gaussian beam on the lateral and axial resolution have been analyzed in detail. It is proved that RIKES confocal microscopy has high sensitivity and high resolution, besides capability to characterize inherent structural features, such as vibration mode, vibration orientation, and optically induced molecular reorientation etc. Therefore, nonlinear Raman confocal microscopy that is based on RIKES has potential to provide a novel characteristic imaging method comparable to the existing imaging techniques based on other nonlinear optical processes, such as two-photon fluorescence, second harmonic generation (SHG) and coherent anti-Stoke Raman scattering (CARS).     

Imaging and Reconstruction for Rough Surface Scattering in the Kirchhoff Approximation by Confocal Microscopy

Abstract

Imaging of rough surfaces in confocal microscopy can be described using the concept of the three-dimensional (3D) coherent transfer function (CTF), which is developed on the basis of the Kirchhoff approximation. The 3D CTF is presented using a scalar but high-angle theory. Methods for reconstruction of surface profiles are considered.     

Precipitation (exsolution) in garnet-type oxide

The exsolution process of magnetite in a garnet matrix is described. The intragranular nucleation of magnetite in substituted yttrium iron garnets is characterized by a transitional event. Magnetite nucleates in the centre of zones which constitute a transitional phase fully coherent with the matrix. An ionic process model is proposed for this transitional event. This model is in good agreement with the experimental data obtained in electron microscopy. It is shown that the activation energy barrier is lower for nucleation via a transitional phase.     

Image formation and tomogram reconstruction in optical coherence microscopy

In this work we present a model for image formation in optical coherence microscopy. In the spectral domain detection, each wavenumber has a specific coherent transfer function that samples a different part of the object's spatial frequency spectrum. The reconstruction of the tomogram is usually accurate only in a short depth of field. Using numerical simulations based on the developed model, we identified two distinct mechanisms that influence the signal of out-of-focus sample information. Besides the lateral blurring induced through defocusing, an additional axial envelope contributing equally to the signal degradation was found.     

Multi scale hard x-ray microscopy

The structure of crystalline materials is typically organised hierarchically on several length scales. Hard x-ray microscopy is presented as a collection of modalities that allows to zoom into a mm-sized sample to acquire 3D maps of any embedded region and at essentially all relevant length scales. For coarse mapping of grains, their orientations and average stress state diffraction based tomography methods can sample thousands of grains with a resolution of 2 µm. At the 100 nm scale, domains and dislocations and their associated strain fields can be visualised by diffraction microscopy. Similar to dark field electron microscopy, diffraction and imaging can be combined in several ways. For the ultimate resolution, a bulk version of coherent diffraction imaging is introduced. Hard x-ray microscopy is optimised for acquisition of 3D movies: directly visualising the structural changes during nucleation and growth, deformation or damage. The state of art is provided along with examples of use. I discuss how hard x-ray microscopy studies can enable the formulation and validation of improved multiscale models that account for the entire heterogeneity of materials.     

复合纳米金膜的制备及其光学性质

本文利用化学还原法制备了不同尺寸的金纳米颗粒,并利用离子自组装多层技术在玻璃基底上沉积了基于金纳米颗粒的复合纳米金膜,研究了颗粒尺寸和成膜厚度对复合金膜光学性质的影响。不同比例的柠檬酸钠与氯金酸产生的金纳米颗粒溶液的紫外-可见光谱随着金颗粒直径增大而红移展宽。适量比例的柠檬酸钠与氯金酸能够产生平均直径为14±1.2nm且尺寸分布均匀的金纳米球;其溶液在518nm处有一特征吸收峰。不同大小的金纳米颗粒形成的薄膜的紫外-可见光谱形状不同,局域表面等离子体共振峰的位置随着颗粒直径的减小而向短波方向迁移。薄膜的沉积层数越多,薄膜表面的颗粒分布越均匀,局域表面等离子体峰的峰值变化也将减小。本工作证实了利用离子自组装多层技术能够快速、简易、低成本地在玻璃基底上沉积具有局域表面等离子体共振的复合纳米金膜。     

Shot-noise influence on the reconstructed phase image signal-to-noise ratio in digital holographic microscopy

In digital holographic microscopy, shot noise is an intrinsic part of the recording process with the digital camera. We present a study based on simulations and real measurements describing the shot-noise influence in the quality of the reconstructed phase images. Different configurations of the reference wave and the object wave intensities will be discussed, illustrating the detection limit and the coherent amplification of the object wave. The signal-to-noise ratio (SNR) calculation of the reconstructed phase images based on the decision statistical theory is derived from a model for image quality estimation proposed by Wagner and Brown [Phys. Med. Biol. 30, 489 (1985)]. It will be shown that a phase image with a SNR above 10 can be obtained with a mean intensity lower than 10 photons per pixel and per hologram coming from the observed object. Experimental measurements on a glass-chrome probe will be presented to illustrate the main results of the simulations.     

Partially coherent image formation with x-ray microscopes

Image formation with partially coherent radiation is evaluated with the Hopkins formula and then applied to x-ray microscopy. Image characteristics expected from instruments with circular and annular pupils in partially coherent conditions are considered for two-point objects and a knife-edge object. The theoretically expected values for image characteristics that are easy accessible by an experiment, such as the width of a knife edge, are given for various x-ray microscopes.     

Three-dimensional coherent transfer function for reflection confocal microscopy in the presence of refractive-index mismatch

The three-dimensional (3-D) coherent transfer function for reflection confocal microscopy of high-numerical-aperture objectives is derived and calculated in the presence of refractive-index mismatch when a laser beam is focused into a medium of refractive index different from its immersion medium. This aberrated coherent transfer function is then used to estimate the readout efficiency of 3-D data bits recorded in a thick medium. It is shown that the readout efficiency of confocal microscopy for 3-D bit data storage is decreased with the focal depth of an objective in a recording medium. However, a high readout efficiency can be maintained if the tube length of a reading objective is linearly altered to compensate for the spherical aberration caused by the refractive-index mismatch.     

Two-dimensional imaging theory of confocal self-interference microscopy

A two-dimensional coherent imaging equation is derived for confocal self-interference microscopy (CSIM), which uses a birefringent material to generate an interference pattern in the detection optics. This interference pattern, called a self-interference pattern, sharpens the point-spread function (PSF) along the lateral direction. To derive the imaging equation, an equation for the self-interference pattern is derived. Numerical simulation results based on the imaging equation are presented. One-point response results show a 42.8% reduction in the FWHM of the lateral PSF. Two-point response results show a nearly twofold improvement in two-point resolution.     

Spin Path Integrals, Berry Phase, and the Quantum Phase Transition in the Sub-Ohmic Spin-Boson Model

The quantum critical properties of the sub-Ohmic spin-1/2 spin-boson model and of the Bose-Fermi Kondo model have recently been discussed controversially. The role of the Berry phase in the breakdown of the quantum-to-classical mapping of quantum criticality in the spin-isotropic Bose-Fermi Kondo model has been discussed previously. In the present article, some of the subtleties underlying the functional integral representation of the spin-boson and related models with spin anisotropy are discussed. To this end, an introduction to spin coherent states and spin path integrals is presented with a focus on the spin-boson model. It is shown that, even for the Ising-anisotropic case as in the spin-boson model, the path integral in the continuum limit in the coherent state representation involves a Berry phase term. As a result, the effective action for the spin degrees of freedom does not assume the form of a Ginzburg-Landau-Wilson functional. The implications of the Berry-phase term for the quantum-critical behavior of the spin-boson model are discussed. The case of arbitrary spin S is also considered.     

Longitudinal wave scattering from rough crack-like defects

The roughness of crack-like defects affects ultrasonic wave scattering and this, in turn, affects defect detection and characterization. The first part of this paper is concerned with the efficient numerical modeling of scattering from rough cracks, i.e., a finite element local scattering (FELS) model. The scattered field is presented in the form of a scattering matrix, which describes the far-field scattering coefficient for all possible combinations of incident and scattering directions. The scattering matrices for many different realizations of rough cracks are simulated using both a FELS model and a model based on the Kirchhoff approximation. It is shown that the difference between scattering matrices extracted from the Kirchhoff model and the FELS model is less than 8%, for rough cracks with a standard deviation less than 0.3 wavelengths and a correlation length longer than 0.5 wavelengths, at incident and scattering angles ranging from -80° to 80° relative to the normal direction of the mean surface. Because the Kirchhoff model is significantly more efficient than the FELS model, it is used for subsequent simulations in which many realizations of rough cracks are studied to gain insight into the statistical nature of the scattering process. In line with previous work, a distinction is made between the coherent and diffuse contributions to the overall scattered field, in which the former represents the ensemble average over multiple surface realizations. The coherent and diffuse contributions of scattered field from various types of rough cracks are simulated. It is shown that surface roughness directly affects the coherent contribution to scattering behavior, whereas the diffuse contribution is affected by both surface roughness and correlation length, especially for rougher cracks.     

Detection of chemical interfaces in coherent anti-Stokes Raman scattering microscopy: Dk-CARS. I. Axial interfaces

We develop a full vectorial theoretical investigation of the chemical interface detection in conventional coherent anti-Stokes Raman scattering (CARS) microscopy. In Part I, we focus on the detection of axial interfaces (i.e., parallel to the optical axis) following a recent experimental demonstration of the concept [Phys. Rev. Lett. 104, 213905 (2010)]. By revisiting the Young's double slit experiment, we show that background-free microscopy and spectroscopy is achievable through the angular analysis of the CARS far-field radiation pattern. This differential CARS in k space (Dk-CARS) technique is interesting for fast detection of interfaces between molecularly different media. It may be adapted to other coherent and resonant scattering processes.     

Role of coherent structures in turbulent shear flows

A definition for the large-scale coherent structure is presented, and the nature and role of coherent structures in turbulent shear flows are examined. The equations governing the coherent motions and the experimental considerations as well as constraints in the investigations of coherent structures in wall-bounded and free turbulent shear flows are discussed. Results from a few of our recent and ongoing studies of coherent structures in excited and unexcited free turbulent shear flows are reviewed. These results show that coherent structures are dominant in transport in the early stages of their formation, but not in the self-preserving regions of turbulent shear flows.     

Microstructural damage due to dynamic loading of Cu-Co dispersion alloys

Transmission electron microscopy techniques have been employed to study the microstructural changes accompanying deformation and spallation during the dynamic loading of Cu-Co dispersion alloys. Alloys aged to produce coherent precipitate particles exhibited a loss of coherency and apparent precipitate enlargement after being subjected to dynamic loading conditions. Over-aged alloys containing incoherent precipitates exhibited precipitate growth, dislocation entanglements and void initiation in the matrix adjacent to precipitate-matrix interfaces. The superior spallation resistance of alloys containing fine coherent precipitates is attributed to the difficulty of void nucleation at low misfit interfaces which can accommodate dislocation cutting and offer preferred sinks for excess vacancies. A model based on the generation of excess lattice vacancies during dynamic loading is described to account for the observation of particle enlargement and loss of coherency, as well as the preferred initiation of voids adjacent to incoherent particles.