Gaussian Beam

In optics, a Gaussian beam is a beam of electromagnetic radiation whose transverse electric field and intensity (irradiance) distributions are described by Gaussian functions. Many lasers emit beams with a Gaussian profile, in which case the laser is said to be operating on the fundamental transverse mode, or "TEM00 mode" of the laser's optical resonator. When refracted by a lens, a Gaussian beam is transformed into another Gaussian beam (characterized by a different set of parameters), which explains why it is a convenient, widespread model in laser optics.
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A beam of light whose electric field intensity distribution is gaussian. Note: When such a beam is circular in cross section the intensity at distance r from the center, E (r ), is given by where E (0) is the electrical field strength at the beam center, i.e. , at r = 0; and w is the value of r at which the intensity is 1/e of its value on the axis.