It is shown that the homogeneous scalar wave equation under a generalized paraxial approximation admits of Gaussian beam solutions that can propagate with an arbitrary speed, either subluminal or superluminal, in free-space. In suitable moving inertial reference frames, such solutions correspond either to standard stationary Gaussian beams or to "temporal" diffracting Gaussian fields.
No takes yet. Share an insight, caveat, or question.
Stefano Longhi (2004) studied this question.
Synapse has enriched 3 closely related papers on similar clinical questions. Consider them for comparative context: