  We calculate the radiation spectrum off a qq-bar pair of a fixed opening
angle theta_qq-bar traversing a medium of length L. Multiple interactions with
the medium are handled in the harmonic oscillator approximation, valid for soft
gluon emissions. We discuss the time-scales relevant to the decoherence of
correlated partons traversing the medium and demonstrate how this relates to
the hard scale that govern medium-induced radiation. For large angle radiation,
the hard scale is given by Qhard = max(r_perp^{-1}, Qs), where r_perp =
theta_qq-bar L is the probed transverse size and Qs is the maximal transverse
momentum accumulated by the emitted gluon in the medium. These situations
define in turn two distinct regimes, which we call "dipole" and "decoherence"
regimes, respectively, and which are discussed in detail. A feature common to
both cases is that coherence of the radiation is restored at large transverse
momenta, k_\perp > Qhard.
