| diffraction | When a wave train passes an obstacle secondary waves are set up that interfere with the primary wave and give rise to bands of constructive and destructive interference. Around a point source of light, in consequence, is a series of concentric light and dark bands (coloured bands with white light), a diffraction pattern. (18 Nov 1997) |
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| diffraction grating | <microscopy> An artificially produced periodic array of scattering centres capable of producing a pattern of diffracted energy, such as accurately ruled lines on a plane surface. (05 Aug 1998) |
| grating, diffraction | <microscopy> A series of narrow, close, equally spaced, diffracting slits or grooves capable of dispersing light into its spectrum. Diffraction gratings and their replicas are also used as standards in micrometry, especially in electron microscopy. (05 Aug 1998) |
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| Convergent Beam Electron Diffraction | <microscopy> An electron probe is tightly focused on a transmission electron microscopy specimen and the resulting pattern of diffracted electrons is observed. The patterns contains information on the crystal symmetry and atomic and electronic structure of the sample. Regions as small as 0.2 nm may be examined. Acronym: CBED (05 Aug 1998) |
| X-ray diffraction | <investigation> Basis of powerful technique for determining the three dimensional structure of molecules, including complex biological macromolecules such as proteins and nucleic acids, that form crystals or regular fibres. Low angle X-ray diffraction is also used to investigate higher levels of ordered structure, as found in muscle fibres. (18 Nov 1997) |
| Selected Area Electron Diffraction | <technique> In this diffraction mode an aperture is used to define the area from which a diffraction pattern is to be recorded from a thin sample. This aperture is typically located in an image plane below the sample. Selected Area Electron Diffraction patterns are simple spot patterns and are of use in phase determination (lattice spacing measurement) and defect analysis (sample orientation). Acronym: SAED (05 Aug 1998) |
| interference diffraction patterns | The patterns arising from the recombination of beams of light or other waves after they have been split and one set of rays have undergone a phase retardation relative to the other. Such patterns formed by simple objects give information on the correctness of the focus and the presence or absence of optical defects. (18 Nov 1997) |
| optical diffraction | A technique used to obtain information about repeating patterns. Diffraction of visible light can be used to calculate spacings in the object. (18 Nov 1997) |
| three-dimensional diffraction pattern | <optics> The diffraction pattern (of a point source) that appears in the three-dimensional space in and near the focal plane. For an aberration-free, diffraction- limited system, the slice of the diffraction pattern in the focal plane is the Airy disk and its surrounding diffraction rings. Above and below focus, the pattern changes periodically along the axis of the light beam so that bright and dark Airy-disk-like patterns appear alternately. The axial period of repeat is spaced twice as far apart as the radial period of repeat in the Airy disk and its diffraction rings (05 Aug 1998) |
| electron diffraction | <technique> The phenomenon, or technique of producing diffraction patterns through the incidence of electrons upon matter. (05 Aug 1998) |