# Rayleigh length (range)

## Description

In optics and especially laser science, the Rayleigh length or Rayleigh range is the distance along the propagation direction of a beam from the waist to the place where the area of the cross section is doubled.

Rayleigh length is particularly important when beams are modeled as Gaussian beams. For a Gaussian beam propagating in free space along the z-axis, the Rayleigh length is depended on the wavelength and the radial size of the beam at its narrowest point.

## Variables

z_{R} | Rayleigh length (m) |

π | pi |

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

λ | The wavelength (m) |