  Semi-classical calculation of an oscillating dipole induced in a two-level
atom indicates that spherical radiation from the dipole under coherent
interaction, i.e., Rayleigh scattering, has a power level comparable to that of
spontaneous emission resulting from an incoherent process. Whereas spontaneous
emission is nearly isotropic and has random polarization generally, Rayleigh
scattering is strongly anisotropic and polarized in association with incident
light. In the case where Rabi frequency is much larger than frequency detuning
and spontaneous emission rate, while the power of spontaneous emission varies
with time at the Rabi frequency, the power of Rayleigh scattering oscillates at
twice the Rabi frequency. Moreover, the radiation pressure force acting on an
atom due to Rayleigh scattering exceeds that caused by spontaneous emission
when frequency detuning is large.
