Topic
Fresnel zone
About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.
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TL;DR: Two different methods thatuse Twin-CGHs for absolute testing of aspheric surfaces are described, and a mutual comparison of the two results and a comparison with the established N-position rotation test are given.
Abstract: A complete absolute interferometric test of axially symmetric aspheres is presented. The method is based on a specially designed computer-generated hologram (CGH) that reconstructs an aspherical wave as well as a spherical auxiliary wave. Since both phase functions have the same symmetry and their pattern is simultaneously encoded, we call this type of multiplex hologram a Twin-CGH. The spherical wave is used for calibration. The aberrations of the spherical auxiliary wave are measured absolutely with either a spherical mirror or an absolute test for Fresnel zone plates. Thus the two types of aberration inherent in the CGH can be identified and separated from each other. The errors of the spherical wave can be transferred to those of the aspherical wave. Two different methods that use Twin-CGHs for absolute testing of aspheric surfaces are described. Test procedures are explained, equations are derived, and experimental results are presented. A mutual comparison of the two results and a comparison with the established N-position rotation test are given.
64 citations
TL;DR: An analytical model of the aperture is developed and used to analyze the diffracted order characteristics of the holographic metasurface aperture, showing high-fidelity focusing patterns even for difficult focusing scenarios across the entire investigated field-of-view.
Abstract: We present numerical simulations of the near-field focusing capabilities of a dynamically reconfigurable holographic metasurface aperture. The aperture consists of a parallel-plate waveguide in which the upper plate is patterned with a number of metamaterial irises that can be dynamically switched between radiating (ON) and non-radiating (OFF) states. A cylindrically symmetric waveguide mode, excited by a coaxial probe in the center of the lower plate, serves to excite the radiating irises, forming a focused spot in the radiating near-field (or Fresnel zone). The layout of the metamaterial elements and their tuning states is determined using holographic design principles, in which the interference pattern of the waveguide (or reference) mode and the desired radiated field pattern leads to the required phase distribution over the surface of the aperture. We also develop an analytical model of the aperture to confirm the numerical simulations, and to illustrate the advantage of the guided-mode as the reference wave versus a plane-wave. We further leverage this analytical model to analyze the diffracted order characteristics of the holographic metasurface aperture, showing high-fidelity focusing patterns even for difficult focusing scenarios across the entire investigated field-of-view.
63 citations
TL;DR: It is shown that an on-chip microscope system capable of fluorescence microscopy imaging of samples in fluid media can be used to image the cell nuclei stained by Acridine Orange and cytoplasm labeled by Qtracker(®).
Abstract: We report the implementation of an on-chip microscope system, termed fluorescence optofluidic microscope (FOFM), which is capable of fluorescence microscopy imaging of samples in fluid media. The FOFM employs an array of Fresnel zone plates (FZP) to generate an array of focused light spots within a microfluidic channel. As a sample flows through the channel and across the array of focused light spots, the fluorescence emissions are collected by a filter-coated CMOS sensor, which serves as the channel's floor. The collected data can then be processed to render fluorescence microscopy images at a resolution determined by the focused light spot size (experimentally measured as 0.65 μm FWHM). In our experiments, our established resolution was 1.0 μm due to Nyquist criterion consideration. As a demonstration, we show that such a system can be used to image the cell nuclei stained by Acridine Orange and cytoplasm labeled by Qtracker®.
63 citations
TL;DR: In this article, a numerical study of elastic wave propagation in weakly anisotropic het- erogeneous media was conducted to investigate the validity of different assumptions made in the derivation of these kernels.
Abstract: SUMMARY Splitting intensity, a new seismic observable that characterizes seismic anisotropy, can be ex- pressed as linear combinations of elastic perturbations involving 3-D sensitivity (or Frechet) kernels. We conduct a numerical study of elastic wave propagation in weakly anisotropic het- erogeneous media in order to investigate the validity of the different assumptions made in the derivation of these kernels. For characteristic periods larger than 6 s, the splitting parame- ters obtained from the analysis of synthetic seismograms calculated using a spectral-element method (SEM) are in excellent agreement with predictions based upon the 3-D kernels. This suggests that the kernels fully capture the complexity of shear wave splitting in heterogeneous anisotropic media and can be used for tomography. In addition, they can be used to calculate synthetic splitting parameters in 3-D anisotropic media, which represents a very small amount of computation compared with finite-difference or finite-element modelling. 3-D kernels dis- tribute sensitivity off of the reference ray given by the laws of geometrical optics. This has important consequences for the interpretation of apparent splitting parameters, which usually relies on ray theory. Apparent splitting parameters estimated at the surface can differ signif- icantly from the anisotropic properties in the underlying medium wherever heterogeneities occur with a characteristic wavelength smaller than approximately 0.75 times the width of the first Fresnel zone √ λz, with λ the wavelength and z the depth.
63 citations
TL;DR: In this paper, the authors reported the successful computational determination of structural detail in a simple transparent object through holographic measurement of scattered monochromatic light, where the complex disturbance of the scattered light was measured along a line transverse to the illumination in the Fresnel zone of the object.
Abstract: This paper reports the successful computational determination of structural detail in a simple transparent object through holographic measurement of scattered monochromatic light. The complex disturbance of the scattered light is measured in amplitude and phase, along a line transverse to the illumination in the Fresnel zone of the object. The scattering potential of the object is then calculated along a parallel line using the field data and a new inverse scattering theory. The results agree well with the known parameters of the two test objects, a high-quality and a low-quality right parallelepiped aligned with two faces normal to the illumination. This experiment is believed to be the first which includes the quantitative reconstruction of structure in a physical object from measurement of scattered light. The technique is somewhat similar to that employed in connection with reconstruction of crystal structures from x-ray diffraction experiments.
63 citations