The beam divergence of an electromagnetic
beam is the increase in
beam diameter with distance from the
aperture from which the beam emerges in any plane that intersects the beam axis. Beam divergence is usually used to characterize electromagnetic beams in the optical regime, in other words cases in which the aperture from which the beam emerges is very large with respect to the
wavelength. Beam divergence usually refers to a beam of circular cross section, but not necessarily so. A beam may, for example, have an elliptical cross section, in which case the orientation of the beam divergence must be specified, for example with respect to the major or minor axis of the elliptical cross section.
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Of an electromagnetic
beam , in any plane that intersects the beam axis, the increase in
beam diameter with distance from the
aperture from which the beam emerges. Note 1: Beam divergence is usually used to characterize electromagnetic beams in the optical regime, i.e., cases in which the aperture from which the beam emerges is very large with respect to the
wavelength . Note 2: Beam divergence usually refers to a beam of circular cross section, but not necessarily so. A beam may, for example, have an elliptical cross section, in which case the orientation of the beam divergence must be specified, e.g., with respect to the major or minor axis of the elliptical cross section.