  We propose and analyze theoretically a resonant acousto-optic Stark effect
for microcavity (MC) polaritons parametrically driven by a surface acoustic
wave. For GaAs-based microcavities our scheme ``acoustic pumping - optical
probing'' deals with surface acoustic waves of frequency $\nu_{\rm SAW} \simeq
0.5 - 3$ GHz and intensity $I_{\rm SAW} \simeq 0.1 - 10$ mW/mm. The
acoustically-induced stop gaps in the MC polariton spectrum drastically change
the optical response of MC polaritons. Because an acoustically pumped intrinsic
semiconductor microcavity remains in its ground electronic state, no many-body
effects screen and weaken the resonant acousto-optic Stark effect. In the
meantime, this allows us to work out an exactly-solvable model for resonant
acousto-optics of MC polaritons which deals with giant acousto-optical
nonlinearities. Finally, we discuss possible applications of the proposed
resonant acoustic Stark effect for optical modulation and switching and
describe an acousto-optic device based on a (GaAs) microcavity driven by a
surface acoustic wave.
