We report experimental studies of electromagnetically induced transparency
in A-type and ladder-type atomic systems realized in Rb-87 atoms cooled and
confined in a magneto-optical trap, Complete transparency is observed in t
he A-type system with a moderate coupling field. Comparison between the two
systems reveals that at the line center of a weak probe transition, destru
ctive interference occurs for the A-type system, whereas constructive inter
ference occurs for the ladder-type system. We discuss conditions of complet
e transparency in the A-type system that contains hyperfine magnetic sublev
els. Our experimental measurements for the two systems agree with theoretic
al calculations based on simple three-level A-type and ladder-type models.
(C) 2001 Optical Society of America.