  We present an extension of the two-point optical microrheology technique
introduced by Crocker \textit{et al.} [Phys. Rev. Lett. \textbf{85}, 888
(2000)] to high frequencies. The correlated fluctuations of two probe spheres
held by a pair of optical tweezers within a viscoelastic medium are determined
using optical interferometry. A theoretical model is developed to yield the
frequency-dependent one- and two-particle response functions from the
correlated motion. We demonstrate the validity of this method by determining
the one- and two-particle correlations in a semi-dilute solution of polystyrene
in decalin. We find that the ratio of the one- and two-particle response
functions is anomalous which we interpret as evidence for a slip boundary
condition caused by depletion of polymer from the surface of the particle.
