Shaping optical beams with non-integer orbital-angular momentum: a generalized differential operator approach.

We introduce an analytical procedure to construct an optical beam with an arbitrary value of orbital-angular momentum (OAM) by keeping the flexibility of shaping its transverse intensity distribution without changing its OAM. We apply the general theory of fractional differential operators in Fourier domain to derive general expressions for the OAM content in the beam and find the relevant parameters that determine its OAM value and those that can be freely modified without affecting it.