Enhanced multiwave mixing processes due to atomic coherence have been experimentally reported in several multilevel atomic systems.[1-3] The keys in such enhanced nonlinear optical processes include greatly reduced linear absorption of the generated optical fields due to electromagnetically induced transparency (EIT).A great deal of attention has been paid to observation and understanding of EIT and related effects in multilevel atomic systems interacting with electromagnetic fields.[4-9] Therein,the AutlerTownes (AT) splitting in multilevel atomic system has been investigated.[10] Theoretical and experimental studies indicate that the AT-split Rydberg population can lead to an antiblockade effect.[11,12] Such an AT splitting effect has also been investigated by detecting fluorescence in lithium molecules using cw triple-resonant spectroscopy.