  We present an experimental method allowing to quantify slip at the wall in
viscous polymer fluids, based on the observation of the evolution under simple
shear flow of a photobleached pattern within a fluorescent labeled polymer
melt. This straightforward method provides access to slip length at top and
bottom interfaces in the 1 $\mu$m to 1 mm range and to the actual shear rate
experienced by the fluid. Based on simple optical imaging and image analysis
techniques, this method affords an improvement compared to previously reported
methods in which the photobleached fluorescence intensity profiles before and
after shear were compared and measured by scanning a photomultiplier. The
present method relies on a direct determination of the displacement profile
inside the polymer fluid from an analysis of the 3D evolution of the whole
photobleached pattern. We demonstrate the potential of this method with
measurements of the slip length for an entangled PDMS melt, as a function of
the shear rate, in contact with several weakly surfaces i.e. end-tethered PDMS
or polystyrene (PS) chains, a self-assembled monolayer (SAM) of
trimethoxy(octadecyl)silane (OTS), and a glassy PS thin-film.
