Intensity Distribution Of Diffraction Pattern Research Articles

Development of the Correction Algorithm to Limit the Deformation of Bacterial Colonies Diffraction Patterns Caused by Misalignment and Its Impact on the Bacteria Identification in the Proposed Optical Biosensor.

Recently proposed methods of bacteria identification in optical biosensors based on the phenomenon of light diffraction on macro-colonies offer over 98% classification accuracy. However, such high accuracy relies on the comparable and repeatable spatial intensity distribution of diffraction patterns. Therefore, it is essential to eliminate all non-species/strain-dependent factors affecting the diffraction patterns. In this study, the impact of the bacterial colony and illuminating beam misalignment on the variation of classification features extracted from diffraction patterns was examined. It was demonstrated that misalignment introduced by the scanning module significantly affected diffraction patterns and extracted classification features used for bacteria identification. Therefore, it is a crucial system-dependent factor limiting the identification accuracy. The acceptable misalignment level, when the accuracy and quality of the classification features are not affected, was determined as no greater than 50 µm. Obtained results led to development of image-processing algorithms for determination of the direction of misalignment and concurrent alignment of the bacterial colonies’ diffraction patterns. The proposed algorithms enable the rigorous monitoring and controlling of the measurement’s conditions in order to preserve the high accuracy of bacteria identification.

Mapping inelastic intensities in diffraction patterns of magnetic samples using the energy spectrum imaging technique

We present the quantitative measurement of inelastic intensity distributions in diffraction patterns with the aim of studying magnetic materials. The relevant theory based on the mixed dynamic form factor (MDFF) is outlined. Experimentally, the challenge is to obtain sufficient signal for core losses of 3d magnetic materials (in the 700–900 eV energy-loss range). We compare two experimental settings in diffraction mode, i.e. the parallel diffraction and the large-angle convergent-beam electron diffraction configurations, and demonstrate the interest of using a spherical aberration corrector. We show how the energy spectrum imaging (ESI) technique can be used to map the inelastic signal in a data cube of scattering angle and energy loss. The magnetic chiral dichroic signal is measured for a magnetite sample and compared with theory.

Magnetic Chiral Dichroism Studies using Energy Filtered Images

AbstractWe present the quantitative measurement of inelastic intensity distributions in diffraction patterns with the aim of studying magnetic materials. The original idea of using inelastic signal in a transmission electron microscope to measure magnetic information has been proposed recently by Schattschneider et al [1] and various experimental set-ups can be imagined [2,3]. We focus on a new experimental configuration which we use to acquire and collect a map of the signal with a high signal-to-noise ratio. We will also present the numerical treatments that need to be performed to get spatially accurate information and energy resolution. We will illustrate our method studying iron single crystal and discuss the effects of the drift and non-isochromaticity corrections.

AFM, SEM andin situRHEED study of Cu texture evolution on amorphous carbon by oblique angle vapor deposition

The evolution of the crystal orientation of a Cu film grown on an amorphous carbon substrate without intentional heating under 75±6° oblique angle vapor deposition was investigated ex-situ by atomic force microscopy AFM and scanning electron microscopy SEM, and in-situ by reflection high-energy electron diffraction RHEED. At the initial stage of growth 12 nm thick the diffraction patterns showed uniform rings indicating random nucleations of crystals. With more Cu depositions 100 nm thick the diffraction pattern started to break symmetrically from the middle of the 111 and 200 rings representing the absence of 111 and 200 planes parallel to the substrate. However, after this transition stage, at the thickness of 410 nm, the intensity distribution of diffraction patterns appeared asymmetric about the middle of the rings, which is interpreted as the appearance of a tilted 111 texture. Finally the diffraction patterns developed into separated short arcs and showed only a 1111 ¯10 II-O two-orientation texture. By comparing RHEED patterns with the SEM and AFM images of the final film, we argue that the tilted columns having tilted 111 top faces dominate in the later stage of growth. Furthermore, considering the geometry of crystals and shadowing effects, we argue that the vertices of columns having the highest growth velocity normal to the substrate and therefore receiving the maximum flux will dominate the film growth and determine the tilt angle of the texture and the preference of the azimuthal angle orientation.

Translation symmetry of Fraunhofer diffraction patterns of plane apertures with generalized right angles

A class of apertures of the simplest shape possessing generalized right angles is considered. Based on the geometrical theory of diffraction, the formation of Fraunhofer diffraction patterns for apertures of this class is analyzed. Conditions of the possibility of observing translation symmetry in the intensity distributions in diffraction patterns are formulated.

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This paper describes that the Fraunhofer diffraction patterns, which are generated by the slit aperture formed between a reference knife edge and a polished metal cylinder, are influenced by light reflected from the cylinder surface. An incident and diffracted light is partly reflected at the cylinder surface. To analyze the influence of reflected light, the diffraction patterns are simulated by using a personal computer. The intensity distribution of diffraction pattern used the turned cylinder is measured with a phto-detector. The experimental results agree well with the simulated patterns. When the slit aperture width is reduced, the position of the zeroth diffraction light maximum intensity moves from the center of slit aperture to the direction of the knife edge on the observation plane. The Fraunhofer patterns are mainly influenced by the reflection of the diffracted light.

Evidence for a trimer in the [formula omitted] structure on the Si(111) surface by X-ray diffraction under the nearly normal incidence condition

The structure of the 3 x 3 structure on the Si(111) clean surface has been studied using X-ray diffraction under the nearly normal incidence condition. A thin substrate crystal, about 5 μm in thickness, was used to reduce the background scattering. From the analysis of the intensity distribution of diffraction patterns, evidence for a trimer of Bi atoms was obtained and the distance between Bi atoms forming the trimer was found to be 3.10±0.1 A.

Evidence for a trimer in the √3 × √3 -Bi structure on the Si(111) surface by X-ray diffraction under the nearly normal incidence condition

The structure of the √3 × √3 -Bi structure on the Si(111) clean surface has been studied using X-ray diffraction under the nearly normal incidence condition. A thin substrate crystal, about 5 μ m in thickness, was used to reduce the background scattering. From the analysis of the intensity distribution of diffraction patterns, evidence for a trimer of Bi atoms was obtained and the distance between Bi atoms forming the trimer was found to be 3.10±0.1 Å.

An Experimental Investigation of Diffraction Patterns in Low-fresnel-number Focusing Systems

The intensity distribution of diffraction patterns has been measured for focusing systems of Fresnel numbers near unity. Results, presented in intensity charts and in photographs, are compared with theoretical predictions along the axis and in various planes parallel to the geometric focal plane. Close agreement between them has been obtained.

Diffraction patterns of off-axis gaussian beams in the presence of third-order spherical aberration in the optical system

The intensity distribution of diffraction patterns for off-axis gaussian beams at the image plane of an optical system with third-order spherical aberration is calculated by using the concept of the beam aberration function previously introduced by the present authors. The results show how the peak intensity of the diffraction patterns diminishes and how the transversel focal shift occurs as a function of the incident position of the beams at the pupil plane and their beam size.

Diffraction of partially coherent light by an apodized slit aperture

Fraunhofer diffraction of partially spatially coherent light by an apodized aperture is studied theoretically. The apodized slit aperture takes an amplitude distribution which minimizes the second moment of the intensity diffraction pattern on the condition that the total energy passing through the aperture be constant. For partially coherent light, the sinc, exponential, and gaussian forms of correlation in two points over the diffracting aperture are employed. Results are presented for the intensity distribution of diffraction patterns as functions of amplitude and coherence parameters.

The scattering of electrons by atoms and crystals. II. The effects of finite source size

The new formulation of physical optics developed by Cowley & Moodie (1958) is applied to determine to what extent the intensity distributions in electron diffraction patterns, calculated on the assumption of perfectly coherent incident radiations should be modified to take into account the finite size and incoherence of practical electron sources. A model of an ideally incoherent source is set up. Expressions are derived for the intensity distribution in diffraction patterns obtained under various experimental conditions, including cases where partial coherence is introduced in the illumination of the specimen by the presence of an aperture. Numerical calculations for representative cases indicate that coherence considerations may become important with any extension of present-day high-resolution techniques. (auth)