  We observed electromagnetically-induced-transparency-based four-wave mixing
(FWM) in the pulsed regime at low light levels. The FWM conversion efficiency
of 3.8(9)% was observed in a four-level system of cold 87Rb atoms using a
driving laser pulse with a peak intensity of approximately 80 {\mu}W/cm^2,
corresponding to an energy of approximately 60 photons per atomic cross
section. Comparison between the experimental data and the theoretical
predictions proposed by Harris and Hau [Phys. Rev. Lett. 82, 4611 (1999)]
showed good agreement. Additionally, a high conversion efficiency of 46(2)% was
demonstrated when applying this scheme using a driving laser intensity of
approximately 1.8 mW/cm^2. According to our theoretical predictions, this FWM
scheme can achieve a conversion efficiency of nearly 100% when using a dense
medium with an optical depth of 500.
