We applied our pictorial approach using the fundamental concept of the Huck
el molecular orbital theory to the population inversion in the multilevel s
ystems by the straddling-STIRAP (S-STIRAP). We showed that the mechanism of
the population inversion in the multilevel system may be easily understood
by our approach. It is also shown that our approach is useful to understan
d that the condition required for the laser frequency in the delayed pulse
sequence is different for the even- and odd-level systems. (C) 2000 John Wi
ley & Sons, Inc.