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.
© 1996 Optical Society of America
F. Gori, S. Vicalvi, M. Santarsiero, and R. Borghi, "Shape-invariance range of a light beam," Opt. Lett. 21, 1205-1207 (1996)