[new term] convergent beam
Terms to be defined here:
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Disc of least confusion -
Airy disc -
Monochromatic beam -
Coherent beam -
Convergent beam -
Focused beam -
Convergence angle
move to new issue:
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electron diffraction -
convergent beam diffraction -
large-angle convergent-beam electron diffraction
current set of definitions:
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Disc of least confusion:
- def. A cross section of a beam which has the smallest spatial extend.
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Airy disc:
- def. A disc of least confusion which has the theoretically smallest possible extend considering diffraction limits.
- comment. This term is predominantly used in laser and light microscopy. It depends on the optical system used to manipulate a beam as well as the properties of the beam that is being manipulated.
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Monochromatic beam:
- def. A beam which consists of particles of the same energy.
- comment. According to the wave particle dualism the here given definition translates also to a beam which consists of waves having the same wavelength.
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Coherent beam:
- def. A monochromatic beam which consists of waves that have a defined phase relationship.
- comment. The term waves in this definition refers to partial waves.
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Convergent beam:
- def. A beam which is conically shaped such that it's cross section is decreased to form a disc of least confusion.
- comment. To manipulate the direction and intensity of beam particles a lens is required. Using an aperture may decrease the cross section of a beam but will not serve to create a convergent beam.
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Focused beam:
- def. A convergent beam which originates from a coherent beam and which cross section is decreased to the practically smallest possible disc of least confusion.
- comment. The terms focused beam and convergent beam are colloquially often used almost interchangeably. Here we differentiate these terms by pointing to focused beams being used with the intention to direct the beam to the physically smallest possible extend.
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Convergence angle
- def. The angle which is present in a convergent beam and given by the semi-opening angle of the cone.