  We propose a procedure to achieve a complete energy conversion between laser
pulses carrying orbital angular momentum (OAM) in a cloud of cold atoms
characterized by a double-\Lambda atom-light coupling scheme. A pair of
resonant spatially dependent control fields prepare atoms in a
position-dependent coherent population trapping state, while a pair of much
weaker vortex probe beams propagate in the coherently driven atomic medium.
Using the adiabatic approximation we derive the propagation equations for the
probe beams. We consider a situation where the second control field is absent
at the entrance to the atomic cloud and the first control field goes to zero at
the end of the atomic medium. In that case the incident vortex probe beam can
transfer its OAM to a generated probe beam. We show that the efficiency of such
an energy conversion approaches the unity under the adiabatic condition. On the
other hand, by using spatially independent profiles of the control fields, the
maximum conversion efficiency is only 1/2.
