The relationship between the mode content and the fractional Fourier and fractional Hankel transforms of a function is established. It is shown that the Laguerre-Gauss spectrum of a rotationally symmetric wavefront can be determined from its fractional Hankel transforms taken at the optical axis.
PDF version of the full paper
http://www.opticsinfobase.org/abstract.cfm?URI=ol-24-17-1206