A light beam or beam of light is a narrow cone of light energy
radiating from a small source. In optics, a ray is an idealized
narrow beam of light.
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A light beam or beam of light is a narrow cone of light energy
radiating from a small source. In optics, a ray is an idealized
narrow beam of light.
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David C. Carey has written:
'The optics of charged particle beams' -- subject(s): Beam
optics, Particle beams
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An aperature OS size a illluminated by a parallel beam sends diffracted light into a angle of approximately ~y/a. This is the angular size of the bright central maximum. In trevelling a distance z, the diffracted beam therefore acquires a width zy/a due to diffraction. this gives distance beyond which divergence of the beam of width a becomes significant. Therefore, z ~ a2/y we define a quantity ZF called the Fresenls distance by the following equation ZF= a2/y
For distance greater than ZF the spreading due to diffraction over that due to ray optics. The above equation shows that ray optics is valid in the limit of wavelength tending to zero.