  We study the harmonic entanglement and squeezing in a two-mode radiation
produced in a degenerate parametric down conversion process coupled to a
two-mode vacuum reservoir employing the linearization procedure. It is found
that there is a quadrature entanglement between the harmonically related
fundamental and second-harmonic modes and the superimposed radiation exhibits a
significant two-mode squeezing. The entanglement exits even when there is no
two-mode squeezing, since the correlation leading to these phenomena are
essentially different. In addition, the more the external coherent light is
down converted, the more stronger the entanglement and mean photon number of
the two-mode radiation would be which is not generally true for squeezing.
