  A theoretical model describing the Raman scattering process in atomic vapors
is constructed. The treatment investigates the low-excitation regime suitable
for modern experimental applications. Despite the incorporated decoherence
effects (possibly mode dependent) it allows for a direct separation of the time
evolution from the spatial degrees of freedom. The impact of noise on the
temporal properties of the process is examined. The model is applied in two
experimentally relevant situations of ultra-cold and room-temperature atoms.
The spatial eigenmodes of the Stokes photons and their coupling to atomic
excitations are computed. Similarly, dynamics and the waveform of the
collective atomic state are derived for quantum memory implementations.
