  Based on a multi-particle-state stimulated Raman adiabatic passage approach,
a comprehensive theoretical study on the ultrafast optical manipulation of
electron spins in quantum wells is presented. In addition to corroborating the
experimental findings [Science {\bf 292}, 2458 (2001)], we improve the
expression of the optical-pulse-induced effective magnetic field, in comparison
with the one obtained via the conventional single-particle ac-Stark shift.
Further study of the effect of hole spin relaxation reveals that while the
coherent optical manipulation of electron spin in undoped quantum wells would
deteriorate in the presence of relatively fast hole-spin relaxation, the
coherent control in doped systems can be quite robust against the decoherence.
The implications of present results on quantum dots will also be discussed.
