  Experimental measurements and calculations of STIRAP transfer efficiencies
were made on a sodium gas starting from the $3^2{\rm S}_{1/2}$ electronic
ground state, passing through the $3^2{\rm P}_{1/2}$ and/or the $3^2{\rm
P}_{3/2}$ to the $5^2{\rm S}_{1/2}$ state. The lasers used in the experiments
had a pulse width of several picoseconds and were close to the Fourier
transform limit. Although the linewidth of the laser was much smaller than the
spin orbit splitting between the $3^2{\rm P}_{1/2}$ and $3^2{\rm P}_{3/2}$
states, Experiments and calculations reveal that both 3p states play a role in
the transfer efficiency when the lasers are tuned to resonance through the
$3^2{\rm P}_{1/2}$ state, revealing evidence for quantum interference between
the competing pathways.
