In this paper we present an experiment for measuring the chromatic dierences of the tilt used a for polychromatic laser guide star, a suitable solution to overcome the monochromatic laser guide star limitation: the tilt indetermination. A comparative study between two types of data processing is done: the classical estimation of angle of arrival by the image center of gravity, and a new one: an estimation of tilts by tting a phase map in the polychromatic case. From these studies, expected precision is derived and comparison between simulations and data is done.