# Gaussian beam (Beam width or spot size)

## Description

In optics, a Gaussian beam is a beam of electromagnetic radiation whose transverse electric field and intensity (irradiance) distributions are well approximated by Gaussian functions. For a Gaussian beam propagating in free space, the spot size (radius) will be at a minimum value at one place along the beam axis, known as the beam waist. For a beam of wavelength λ at a distance z along the beam from the beam waist, where the origin of the z-axis is defined, the variation of the spot size can be calculated by the waist size and the Rayleigh range.

Related formulas## Variables

w_{z} | The spot size (m) |

w_{0} | The waist size (m) |

z | The distance along the beam from the beam waist (m) |

z_{R} | The Rayleigh range (m) |