  The tomographic imaging of arbitrary molecular orbitals via high-order
harmonic generation requires that electrons recollide from one direction only.
Within a semi-classical model, we show that extremely short phase-stabilized
laser pulses offer control over the momentum distribution of the returning
electrons. By adjusting the carrier-envelope phase, recollisions can be forced
to occur from mainly one side, while retaining a broad energy spectrum. The
signatures of the semi-classical distributions are observed in harmonic spectra
obtained by numerical solution of the time-dependent Schr\"{o}dinger equation.
