  The interference pattern of a Laguerre Gaussian beam in a double slit
experiment is reported. Whereas a typical laser beam phase front is planar, a
Laguerre Gaussian beam exhibits a wave front that is twisting along the
direction of propagation. This leads to a distorted interference pattern. The
topological charge also called the order of the twisted beam can be then
readily and simply determined. More precisely, the naked eye resolution of the
distortion shift of the interference pattern directly informs about the number
of twists made as well as on the sign of the twist. These results are in very
good agreement with theoretical calculations that offer a general description
of the double slit interference with twisted beams.
