STIRAP in sodium vapor with picosecond laser pulses

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.