An analysis of a non-Gaussian, Gaussian laser beam

摘要

It is possible to construct summations of Laguerre-Gaussian modes which have the appearance of a zero order fundamental Gaussian but which, in fact, have no zero order content. These examples have circulated informally as a warning against trusting a single beam profile measurement as to the indication of the modal content of a given beam. These 'non-Gaussian' Gaussian beams also turn out to be extremely revealing of the fundamental assumptions upon which all modal decompositions and modal-based beam quality measures are based upon. Due to the contrived nature of these beams, they are also subject to some very subtle but important theoretical errors. This paper will rigorously examine a 'non-Gaussian', Gaussian beam in terms of its amplitude and phase characteristics, propagation behavior, M~2 and what it reveals about modal decompositions and modal beam quality measures in general.