  We have studied the temporal behavior of the atomic absorption signal under
resonant excitation with a continuous-wave laser radiation. Measurements done
for D2 line of 85Rb with ~ 1 ns temporal resolution have shown irregular
oscillatory behavior of the transmission signal, which becomes well pronounced
for high laser power, and disappears when the laser is tuned off-resonance.
Application of the fast Fourier transform analysis of the transmission signal
reveals power-dependent frequency peaks, which are shown to be associated with
Rabi frequency. Possible linkage of the observed results with the
phase-to-amplitude noise conversion caused by the the phase fluctuations of
laser field is discussed.
