  A procedure is proposed to control the average and width of the velocity
distribution of ultra-cold atoms. The atoms are set initially in a bound state
of an optical trap formed by an inner red detuned laser and an outer blue
detuned laser. The bound state is later converted into a resonance by a
suitable change of the laser intensities. An optimal time dependence of the
switching process, between the sudden and adiabatic limits, adjusts the final
translational energies to the Lorentzian shape of the resonance state.
