Search results for "Names"
showing 10 items of 6843 documents
Three-dimensional behavior of apodized nontelecentric focusing systems.
2002
The scalar field in the focal volume of nontelecentric apodized focusing systems cannot be accurately described by the Debye integral representation. By use of the Fresnel–Kirchhoff diffraction formula it is found that, if the aperture stop is axially displaced, the focal-volume structure is tuned. We analyze the influence of the apodizing function and find that, whereas axially superresolving pupil filters are highly sensitive to the focal-volume reshaping effect, axially apodizing filters are more inclined to the focal-shift effect.
Structure of Liquids
2014
An Introduction to the description of the static structure of simple liquids is given. The principle quantity, which describes this structure is the structure factor, which can be measured with neutron and X-ray diffraction. The structure factor is the Fourier transform of the radial pair distribution function, which describes the statistics of the atoms around a given one. Several theories are introduced for calculating this quantities. It is shown that the structure of liquid metals is dominated by their hardcore repulsion. In the low-wavenumber limit the structure factor is related to the compressibility of the liquid. In this limit deviations from the hard-core model become importent, w…
Undergraduate experiment with fractal diffraction gratings
2011
We present a simple diffraction experiment with fractal gratings based on the triadic Cantor set. Diffraction by fractals is proposed as a motivating strategy for students of optics in the potential applications of optical processing. Fraunhofer diffraction patterns are obtained using standard equipment present in most undergraduate physics laboratories and compared with those obtained with conventional periodic gratings. It is shown that fractal gratings produce self-similar diffraction patterns which can be evaluated analytically. Good agreement is obtained between experimental and numerical results. © 2011 IOP Publishing Ltd.
High-pressure theoretical and experimental study of HgWO4
2011
HgWO 4 at ambient pressure is characterized using a combination of ab initio calculations, X-ray diffraction and Raman scattering measurements. The effect of low pressure and temperature on the structural stability is analysed. Extending our ab initio study to the range of higher pressures, a sequence of stable phases up to 30GPa is proposed. © 2011 Taylor & Francis.
Investigation of Silicon Carbide Polytypes by Raman Spectroscopy
2014
Abstract Polytypes of colourless and coloured single crystals of silicon carbide (SiC) grown on SiC substrates by chemical vapour deposition are studied using Raman spectroscopy supplemented by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The SEM analysis of the defect stacking faults, inclusions of defects and their distribution has shown that they correlate with the peak positions of the obtained Raman spectra and with the XRD data on the crystal structure
Fourier optical approach to the extraction of morphological parameters from the diffraction pattern of biological cells.
1978
A new procedure for fast quantitative extraction of cell parameters from diffraction patterns was deduced from model calculations and applied to cervical gynecological material. Based on radial scans of the diffraction pattern, the technique permits simultaneous determination of the nuclear and cytoplasmic diameters by Fourier analysis of the radial scanning signals after compensation for the intensity falloff by an amplification proportional to the third power of the radial position in the diffraction plane. Illustrative examples of measurements on exfoliated cells of different types are presented.
Non-Conventional Tunable Spatial Filtering
1987
A virtual display of the Fraunhofer diffraction pattern of any object is formed in the transverse source plane by theyirtual diffracted rays extqn0ing in the region to the left of the screen containing the transparencyl),2). Except for a few cases '')"°), the concept of virtual Fourier transform appears not to have been made use of. The main idea of this paper is, bearing in mind the property referred to in the above paragraph, to describe a novel spatial filtering technique. In this way, one can obtain different filtered images, by simply moving the point source along the optical axis. The basic theory is described below.
Fast and robust phase-shift estimation in two-dimensional structured illumination microscopy.
2019
A method of determining unknown phase-shifts between elementary images in two-dimensional Structured Illumination Microscopy (2D-SIM) is presented. The proposed method is based on the comparison of the peak intensity of spectral components. These components correspond to the inherent structured illumination spectral content and the residual compo- nent that appears from wrongly estimated phase-shifts. The estimation of the phase-shifts is carried out by finding the absolute maximum of a function defined as the normalized peak intensity difference in the Fourier domain. This task is performed by an optimization method providing a fast estimation of the phase-shift. The algorithm stability an…
Superresolved Holographic Microscopy
2008
Superresolution methods in digital holographic microscopy provide a useful tool to overcome the Abbe's diffraction limit when using modest microscope lenses. The process improves the cutoff frequency of the microscope lens by means of the generation of a synthetic aperture based on time multiplexing and using 3 main stages: optical coding, optical decoding, and digital postprocessing. After the whole process, a superresolved image is obtained by Fourier transformation of the synthetic aperture.
A multi-step mechanism and integrity of titanate nanoribbons.
2014
A one-step hydrothermal treatment of TiO2 powders under strongly basic conditions has been used to synthesize titanate nanoribbons. The nanoparticles were thoroughly characterized using several methods including transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectrometry (XPS) to determine their morphological, structural and chemical characteristics. The influence of the nature and size of the TiO2 precursor and of the reaction duration on the formation of the nanoribbons was investigated. The conditions required to obtain only titanate nanoribbons with a width ranging from 100 to 200 nm and several tens of micrometers in length w…