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See also: étendue


Alternative forms[edit]



Borrowing from French étendue


etendue (uncountable)

  1. (physics) A conserved property of the light in an optical system; the product of its cross-sectional area (normal to the direction of propagation) and the solid angle it subtends.
    • 1966, “Advanced Infrared Technology”, in University of Michigan Official Publication[1], volume 67:
      The topics include [] carefully outlining the concepts of etendue, finesse, and their theoretical implications; methods of spectral, spatial, temporal, and polarization discrimination; and application of these topics to search and track systems.
    • 2002, Wolfgang Demtröder, Laser Spectroscopy: Basic Concepts and Instrumentation, page 149:
      The light power transmitted to the detector is proportional to the product of the solid angle Ω and area A in the central plane, which is imaged by the lens onto the aperture (often called the étendue U).
    • 2006, Vivek Bakshi, EUV Sources for Lithography, page 37:
      Entendue is an optical invariant and is called by many different names. One of the names if "light-gathering power." As implied by this terminology, when light enters an optical system with smaller entendue from another optical system with larger entendue, the former optical system fails to transmit some part of the light.

Further reading[edit]