  We show that the phase information contained in coherent phonon oscillations
generated by a laser pulse in a multi- orbital superconductor can be used as an
experimental tool to probe super- conductivity and pairing symmetries. The
phase difference between the normal and superconducting states is proportional
to the superconducting order parameter just below the superconducting
transition temperature, Tc. It also exhibits different behaviors for
superconducting states with different pairing symmetries. In particular, if
there is an orbital-dependent internal sign change state, the phase difference
can have a discontinuous jump below Tc.
