Re: Gouy phase shift, in addition to Gaussian beams, for waves in general is the sign of a converging spherical wave inverted as the converging wave passes through its focus and becomes an expanding spherical wave? If so, if it was a continuous sine wave then it would undergo a 180 degree phase shift. Also, if it was a short pulse, $f$, it would seem that the converging spherical wave, $[1/r]f(t+r/c)$, would become an expanding spherical wave, $[-1/r]f(t-r/c)$, of opposite sign after passing through the focus.
My question: Is this true? If no, why not?
References: http://www.azooptics.com/Article.aspx?ArticleID=880 "The Guoy phase shift is a popular axial phase shift that occurs in a converging light wave when it passes through its focus in propagating from -∞ to +∞ . The Guoy phase shift is an additional phase shift that occurs in the propagation of a Gaussian Beam. The overall Guoy phase shift of a Gaussian beam for going through a focus is π."
update edit 3/19/18, see also:
Huygens' principle and Young's experiment in the propagation of light beams
https://www.researchgate.net/publication/243492626
first page of this reference implies that this is true.
What is an intuitive explanation of Gouy phase? physics.stackexchange question
