  The diffusion of photo-generated holes is studied in a high-mobility
mesoscopic GaAs\ channel where electrons exhibit hydrodynamic properties. It is
shown that the injection of holes into such an electron system leads to the
formation of a hydrodynamic three-component mixture consisted of electrons and
photo-generated heavy and light holes. The obtained results are analyzed within
the framework of ambipolar diffusion, which reveals characteristics of a
viscous flow. Both hole types exhibit similar hydrodynamic characteristics. In
such a way the diffusion lengths, ambipolar diffusion coefficient and the
effective viscosity of the electron-hole system are determined.
