  Cavity-free lasing of N$_2^+$ induced by a femtosecond laser pulse at 800~nm
is nearly totally suppressed by a delayed twin pump pulse. We explain this
surprising effect within the V-scheme of lasing without population inversion. A
fast transfer of population between nitrogen ionic states X$^2\Sigma_g^+$ and
A$^2\Pi_u$, induced by the second pulse, terminates the conditions for
amplification in the system. Appearance of short lasing bursts at delays
corresponding to revivals of rotational wave packets are explained along the
same lines.
