  We present experimental observations of a non-resonant dynamic Stark shift in
strongly coupled microcavity quantum well exciton-polaritons - a system which
provides a rich variety of solid-state collective phenomena. The Stark effect
is demonstrated in a GaAs/AlGaAs system at 10K by femtosecond pump-probe
measurements, with the blue shift approaching the meV scale for a pump fluence
of 2 mJcm^-2 and 50 meV red detuning, in good agreement with theory. The energy
level structure of the strongly coupled polariton Rabi-doublet remains
unaffected by the blue shift. The demonstrated effect should allow generation
of ultrafast density-independent potentials and imprinting well-defined phase
profiles on polariton condensates, providing a powerful tool for manipulation
of these condensates, similar to dipole potentials in cold atom systems.
