Quasi-degenerate four-wave mixing optical phase conjugation was investigate
d in cold cesium atoms confined in a magneto-optical trap. Broad and narrow
resonances were observed in the corresponding spectrum. The broad resonanc
es reveal directly the dressed levels structure of the composite system for
med by atoms and trapping laser field. However, the observed narrow resonan
ces can only be qualitatively understood in terms of Raman processes involv
ing nearly degenerate ground-state levels, indicating the important role pl
ayed by the level degeneracy. (C) 2000 Published by Elsevier Science B.V.