  We study the cubic- (focusing-)quintic (defocusing) nonlinear Schr\"odinger
equation in two transverse dimensions. We discuss a family of stationary
traveling waves, including rarefaction pulses and vortexantivortex pairs, in a
background of critical amplitude. We show that these rarefaction pulses can be
generated inside a flattop soliton when a smaller bright soliton collides with
it. The fate of the evolution strongly depends on the relative phase of the
solitons. Among several possibilities, we find that the dark pulse can reemerge
as a bright soliton.
