title: Shape-invariance range of a light beam.
abstract: A typical axially symmetric light beam on paraxial free propagation maintains the same transverse shape as at the waist plane for a certain range along its axis. We discuss a general procedure for estimating this range.
authors.forename: F
authors.initials: F
authors.lastname: Gori
authors.forename: S
authors.initials: S
authors.lastname: Vicalvi
authors.forename: M
authors.initials: M
authors.lastname: Santarsiero
authors.forename: R
authors.initials: R
authors.lastname: Borghi