We demonstrate efficient nonlinear frequency conversion in atomic Pb v
apor under conditions where the linear susceptibility and the effectiv
e nonlinear susceptibility are of the same order. This is accomplished
by using electromagnetically induced transparency to prepare a near-m
aximal atomic coherence on a Raman transition. This strongly driven tr
ansition is used to convert an intense laser beam from 425 to 293 nm w
ith an efficiency of similar to 40%.