  We have detected and analyzed narrow, high contrast coherent population
trapping resonances, which appear in transmission of the probe monochromatic
light beam under action of the counterpropagating two-frequency laser
radiation, on example of the nonclosed three level {\Lambda}-system formed by
spectral components of the Doppler broadened D2 line of cesium atoms (in the
cell with the rarefied Cs vapor). These nontrivial resonances are determined
directly by the trapped atomic population on the definite lower level of the
{\Lambda}-system and may be used in atomic frequency standards, sensitive
magnetometers and in ultrahigh resolution laser spectroscopy of atoms and
molecules.
