The Nonaberrational Width of the Angular Spectrum of a Field Probing a Layered Object in Confocal Microscopy

Optics and Spectroscopy - The influence of the numerical aperture of a light beam that probes a layered object on the magnitude of the quantity measured with a confocal interference microscope upon...     

The exact response of a two-dimensional flat-layered medium to a probing pulse: An application to a layer stripping reconstruction procedure

Abstract

We consider a simple model problem that can be found in many fields of application such as, for example, reflection seismology. That is we consider an initial boundary value problem on a half-plane for a class of two-dimensional wave equations with a piecewise-constant coefficient. This coefficient describes the flat layered medium under consideration. An initial pulse located on the boundary of the half-plane is used to probe the medium. An integral representation of the solution of this problem is obtained by studying the spectral measures of some differential operators in one variable. This integral representation is exploited to obtain an ‘explicit’ formula for the solution of the problem considered evaluated at the location of the probing pulse. This ‘explicit’ formula is exploited to reconstruct the structure of the medium from its response to a probing pulse via a layer stripping procedure. Some numerical results obtained with this procedure on test problems are shown. The ‘explicit’ formula obtained can be used in several other contexts such as, for example, the study of perturbed flat layered media or the study of random flat layered media.     

Imaging and quantifying transverse flow velocity with the Doppler bandwidth in a phase-resolved functional optical coherence tomography

The Doppler bandwidth extracted from the standard deviation of the frequency shift in phase-resolved functional optical coherence tomography (F-OCT) was used to image the velocity component that is transverse to the optical probing beam. It was found that above a certain threshold level the Doppler bandwidth is a linear function of flow velocity and that the effective numerical aperture of the optical objective in the sample arm determines the slope of this dependence. The Doppler bandwidth permits accurate measurement of flow velocity without the need for precise determination of flow direction when the Doppler flow angle is within +/-15 degrees perpendicular to the probing beam. Such an approach extends the dynamic range of flow velocity measurements obtained with the phase-resolved F-OCT.     

Nano-scale metal multilayers produced by repeated press-rolling

Abstract

Multilayer structured alloys which have a layer thickness less than 10 nm have been produced by the application of repeated pressing and rolling to the initially macroscopically thick layered sample. The TEM observation of a Ag/Fe sample revealed a regular alternate lamination of Ag and Fe with the layer thickness in the range of 10 nm. The measured electrical resistivity showed a large dependence on the applied magnetic field which is characteristic to the composite structure of magnetic and non-magnetic metals in the thickness range of nanometers.     

Thermocapillary deformation of a water layer at local heating

A horizontal water layer of 0.29-0.44 mm thickness, locally heated from the substrate, is investigated. The value of thermocapillary deformation occurring at local heating is measured by an inverted laser scanning confocal microscope Zeiss LSM 510 Meta. The heater in the form of strip of 0.5-mm width, 40-mm length, and 0.5-mm height made of indium oxide is sputtered on a sapphire substrate. The water temperature from the side of the substrate is measured using the infrared scanner Titanium 570M. We studied in detail the effect of the initial layer thickness and heating power on the value of thermocapillary deformation and temperature field. It is shown that deformation increases with an increase in thermal capacity and decrease in the layer thickness. Results of numerical simulation are in good qualitative agreement with the measurement results.     

Confocal microscopy with a volume holographic filter

We describe a modified confocal microscope in which depth discrimination results from matched filtering by a volume hologram instead of a pinhole filter. The depth resolution depends on the numerical aperture of the objective lens and the thickness of the hologram, and the dynamic range is determined by the diffraction efficiency. We calculate the depth response of the volume holographic confocal microscope, verify it experimentally, and present the scanned image of a silicon wafer with microfabricated surface structures.     

大张角共焦换能器对振动声成像的影响*

振动声成像是超声成像的一种重要形式,它可以得到包含共焦区组织的弹性信息和声衰减信息的信号,将接收到的信号用于成像即可获得反映组织特性的图像。该文对大张角共焦换能器作用下振动声成像中声辐射力和切变位移进行了理论计算和数值模拟,并通过改变张角变化及频率大小研究其对声辐射力和切变位移的影响。这项工作为大张角共焦换能器在振动声成像中的应用提供了理论支持。     

Experimental assessment of effectively probed volume in confocal XRF spectrometry using microparticles

Current approaches for assessing a confocal micro-X-rayfluorescence–probing volume involve the use of sharp knife edges, thin films, or wires, which are moved through this volume. The fluorescence radiation excited in the material of the object is measured, and profiles are built to enable the determination of the full width at half maximum in any of the three axes of the excited volume. Such approaches do not provide information on the shape of the volume, and the consequent alignment of both used lenses is made based on the position of the maxima of the registered intensity measurements. The use of particles that are smaller than the interaction volume (isolated enough to prevent the influence of nearby particles) and translated through the interaction volume (3D scan) is presented as an alternative methodology to determine the confocal probing volume. Spherical shaped uranium particles with diameter of 1–3 μm originally produced for scanning electron microscopy analysis calibration purposes were used in this study. The results obtained showed that the effectively probed confocal volume has a distinct prolate spheroidal shape that is longer in the axis of the confocal detector than it is wide on the axes of the plane perpendicular to it. The diameter in the longest axis (tilted accordingly to the angle between the two silicon drift detectors) was found to be approximately 25 μm, whereas the shorter was found about 15 μm each, with a volume of about 3,000 μm³.     

Measurements of the velocity gradient using a laser Doppler phenomenon

This paper reports on a method for measuring the velocity gradient using a laser Doppler phenomenon. The velocity gradient is determined from the velocity difference between two different points of the probing object and is actually obtained from the optical heterodyning of two differently Doppler-shifted scattered light fields from two points of the object having different velocities. The properties of output beat signals are theoretically investigated from their spectral broadening including the effect of the detecting aperture. The preliminary experiment was performed by using a rotating glass disk whose velocity is different from its center to the outside. The experimental results shows the usefulness of the present method for measurements of the velocity gradient.     

Eigenoscillations of an acoustic cavity with a local membrane

On the basis of Strutt’s approach, the problem of eigenoscillations of a gas in a cylindrical cavity with an internal membrane in the presence of a coaxial circular aperture in it (A.N. Fock’s problem) is analyzed. By an adequate numerical?analytical procedure, a high-precision solution is constructed to a boundary value problem for the eigenfrequencies and forms of lower order oscillation modes for various relative values of the aperture radius. A (qualitative and quantitative) correspondence is established to the results known in acoustics as applied to the concept of the “associated mass of an aperture.” New physical effects are obtained on the dependence of the frequencies and forms of long-wavelength oscillations of a gas on the geometric parameters of the system.     

Further comparisons between the conventional and the modified Schwarzschild objectives

The performance of the modified Schwarzschild objective configuration in comparison with the ordinary configuration is further investigated, completing the analysis presented in a previous work, which was concerned with the trend of the image-plane resolution against the numerical aperture. Here, we compare the third-order aberration coefficients in both configurations, illustrating the dependence of each coefficient on both the on-axis object position and the numerical aperture. This conveys the tolerances of the two configurations to lateral and mirrors’ axial misalignments. Also, the nonconcentric mirror configuration is considered and the relative performance confronted with that of the modified configuration. PACS 42.15.Eq; 42.82.Cr     

Transmission incoherent ultrasonic imaging of planar objects

A method of obtaining an ultrasonic image of a planar object with spatial variable transparency is proposed on the basis of the results of measuring the amplitude of the ultrasonic wave during the transmission ultrasonic probing. The case is considered in which the wave diffraction strongly affects the amplitude of the field behind the object and the phase is not measured. Even in the absence of phase information, this method allows one to restore the transparency masks of the planar object. The proposed mathematical apparatus can be also used in radio wave probing. Numerical simulation and processing of the experimental data demonstrated the comparability of this method and the aperture synthesis method using the phase information.     

Near-field measurements of the scattering characteristics of a moving object with doppler filtering of the signal

The scattering characteristics of a moving object can be measured by insonifying it with a tone source and receiving the scattered signal with a linear array positioned in the near zone of the object. Possible algorithms of scattered signal processing aimed at determining the angular dependence of scatterer’s target strength are considered. On the basis of experimental data on the angular and frequency characteristics of reverberation caused by insonification of the water area with a tone source, the possibility of the aforementioned measurements is estimated and the minimal measurable values in the angular dependence of scatterer’s target strength are determined for a water area perturbed by weak wind waves.     

共焦扫描系统扫描深度与厚度失真分析

采用几何光学方法对共焦系统扫描时产生的扫描深度与厚度失真进行了理论分析,对名义扫描深度与实际扫描深度之间的关系进行了研究.以若丹明6G薄膜与玻片组成的多层样品为模型,对其进行了模拟计算,得到了扫描深度与厚度失真与系统数值孔径、折射率和样品厚度之间的关系.在实验上分别采用单光子荧光和双光子荧光作为检测信号,在反射式共焦扫描系统上进行了纵向扫描实验,并与模拟计算的结果进行了比较和分析.     

Effect of transverse object position on the reconstructed image of an aperture-limited in-line hologram

It is experimentally demonstrated that the image resolution from an in-line Fraunhofer hologram degrades appreciably when the centre of the diffraction pattern from a 5-bar resolution target is located asymmetrically in the hologram aperture. This effect is confirmed and analysed using calculated and experimentally measured images from holograms of a one-dimensional wire. Increasing asymmetry results in an increasing error in the measured linewidth, and a reduction of image resolution. A simple model based on average fringe contrast is used to predict this decrease in resolution with transverse object position.     

Approach to Detecting Aberrations in Transcranial Ultrasound Imaging

The presence of cranial bones in the ultrasound propagation path seriously complicates the imaging of tissues and blood vessels of the brain since the bones distort the ultrasound field, introducing phase and amplitude aberrations. Such distortions are not always apparent since complete information about the studied object is fundamentally inaccessible. The article develops a new approach that uses the synthetic aperture method to detect wavefront aberrations. A quantitative parameter is proposed that characterizes the presence of aberrations by measuring the RMS width of the angular intensity distribution. Experimental results were obtained at a frequency of 2 MHz using phantom and in vivo transcranial data. It is shown that in the presence of aberrations, the value of the proposed parameter increases by 22–45% with respect to the theoretical value for the aberrationless case.

     

Profile measurement of a moving object using an improved projection grating phase-shifting profilometry

3-D profile measurement of a moving object using a novel phase-shifting technique is introduced. Digital gratings with two steps phase-shifting are projected periodically onto a measured object surface. The deformed fringe patterns are captured by a frame CCD camera within a short exposure time. By synchronizing the projector and the CCD camera accurately, there is an overlapping part which is the same part of the object among three neighbouring frames. The length of an overlapping part can be controlled as one third of a frame length. Hence the intensity values at the same surface point modulated by three neighbouring gratings can be obtained, and its phase value can be computed by an improved phase-extracting algorithm. The profile of a specimen is detected by the proposed method. Experimental results demonstrate that this method is effective for the profile measurement of a moving object.     

Measurements of axial displacements undergone by a diffusing object in speckle photography

The speckles of the image plane of an object are both radially shifted and decorrelated when the object is axially translated through an amount ?. We demonstrate that this radial shift, which is related to the position of the pupil of the optical system, disappears when the pupil lies in the back focal plane of the imaging lens. However, if the irradiance of the image plane is twice recorded on a photographic plate which is laterally shifted through ζ_H between the exposures, the minimum value of the contrast of the Fourier fringes exhibited by the plate after processing, gives the value of ? if ? is less than a particular value, ?_M which will be defined. Also we propose a new speckle measurement method in which the fringes are automatically removed when ? is greater than ?_M. We record the image of the object illuminated in convergent light through an amplitude diffuser placed in the Fourier plane of the object. The mean speckle speckle size of the diffuser is equal to the mean size of the speckles generated by the object in its Fourier plane.     

基于层状模型的功能梯度板中兰姆波传播研究

功能梯度板中的兰姆波的传播在实际工程中有着非常广泛的应用。采用层状模型研究了兰姆波在材料特性沿厚度方向连续变化的功能梯度板中的传播特性。通过数值计算获得了层状板中兰姆波的色散关系,并与已有结果进行了比较,获得了材料属性沿厚度方向呈指数变化和多项式变化时功能梯度板中兰姆波的波速和位移解。当材料属性连续变化时,兰姆波各阶模态的波速与位移都将发生变化。相比于兰姆波的高阶模态,低阶模态的波速变化更加明显。本文的研究可为功能梯度板的设计提供参考。     

Correction of optical distortions in dry depth profiling with confocal Raman microspectroscopy

We present a generalized approach to obtain improved Raman intensity profiles from in‐depth studies performed by confocal Raman microspectroscopy (CRM) with dry objectives. The approach is based on regularized deconvolution of the as‐measured confocal profile, through a kernel that simulates optical distortions due to diffraction, refraction and collection efficiency on the depth response. No specific shape or restrictions for the recovered profile are imposed. The strategy was tested by probing, under different instrumental conditions, a series of model planar interfaces, generated by the contact of polymeric films of well‐defined thickness with a substrate. Because of the aforementioned optical distortions, the as‐measured confocal response of the films appeared highly distorted and featureless. The signal computed after deconvolution recovers all the films features, matching very closely with the response expected. Copyright © 2011 John Wiley & Sons, Ltd.