We study narrow-band biphoton generation from spontaneous four-wave mixing
with electromagnetically induced transparency in a laser cooled atomic
ensemble. We compare two formalisms in the interaction and Heisenberg pictures,
and find that they agree in the low gain regime but disagree in the high gain
regime. We extend both formalisms accounting the non-uniformity in atomic
density and the driving laser fields. We find that for a fixed optical depth
and a weak and far-detuned pump laser beam, the two-photon waveform is
independent of the atomic density distribution. However, the spatial profiles
of the two driving laser beams have significant effects on the biphoton
temporal waveform. We predict that waveform shaping in time domain can be
achieved by controlling the spatial profiles of the driving laser fields
