Transverse correlation vanishing due to phase aberrations

The concept of transverse correlation vanishing, between the fraction of power contained in the centre and wings of a probe beam, recently introduced [Opt. Commun. 282 (2009) 3854-3858] is important to be considered when measuring the effective focal length of any refractive index profile. When the latter is not parabolic it is shown that the transverse correlation could vanish, and this represents a potential source of error when measuring any lensing effect. We propose a low cost set-up (two photodiodes, a pinhole and a stop) able to reveal if the probe beam has monitored a pure or an aberrated lensing effect especially when it is time-dependent.