  Usually, it's difficult for us to observe the Compton Scattering in an atom.
One way to overcome this difficult is using multi-photon collide with an atom,
which will come into being multi-photon Compton Scattering (MCS) phenomenon.
Thus, we can investigate the MCS process in visible light region. During the
MCS process, the cluster atoms moving as a whole, namely atomic Dicke states,
the multi-photon interacting with cluster atoms. We can observe a significant
Doppler shift of resonant fluorescence spectrum(RFS)in a room-temperature
two-levelatomic system. In this paper, we present a detail analysis of the
physics mechanism of the Doppler shift and propose a method to measure the
component of the Dicke states (the atomic polymers with different masses)by
using the Doppler shift of the RFS.
