Basic concepts of modern quantum optics as of Ramsey-Raman-Rabi spectroscopy through pulses rather than by using a broad single light excitation of two-level atomic/molecular system towards atomic pumping, selection, and interferometer are exposed in an analytical and phenomenological manner.
Top8.2. The Ramsey Effect
One like going beyond the effect of the saturated absorption, evaluated not by soaking in external fields continuously applied, but sequentially, at intervals of time. As long as the amplitude and the phase of the applied external field varies along the direction of investigation, an experimental arrangement in terms of the uniformity of the properties of the applied external field is more advantageous while having applications in narrow regions of the absorption cell.
The Ramsey effect investigates the temporal successive variation (the sequence 
) of the Fourier coefficients that characterize the evolution of an atomic/ molecular assembly between two areas in which has applied the external potential, with a free evolution between them, but causally fixed by the impulses of the fields of the crossed areas.
Considering an atomic/molecular System which at the moment t1 entering in an area subject to a periodic disturbance, inducing a transition between the own molecular states 
& 
.
We allow the extra-diagonal perturbation potential such as (Ramsey 1950):
(8.1) and kinetic energy for the free evolution (free fall):
(8.2)The wave function for molecular assembly for the two levels in cause will be:
(8.3) and Schrodinger equation for the Fourier coefficients will be:
(8.4)Hence, the system:
(8.5)