We analyze the steady-state population inversion in a two-level atom driven
by three laser fields of unequal frequencies. The dependence of the popula
tion inversion on initial relative phases between the driving lasers and ca
ncellation of subharmonic resonances are predicted and explained in terms o
f quantum interference between dressed states of the system. (C) 2000 Elsev
ier Science B.V. All rights reserved.