Radiation from Polarized Atoms. Quantum Beats
In this chapter we will consider the decay of an ensemble of excited atoms by photon emission. We will discuss the following case. We assume that an ensemble of atoms has been excited “instantaneously” at time t = 0. As usual, “instantaneous” implies that the excitation time is short compared to the mean lifetime of the excited states and any characteristic precession frequency (see Sects. 3.5 and 4.7.1).