  We analyze quantum entanglement of Stokes light and atomic electronic
polarization excited during single-pass, linear-regime, stimulated Raman
scattering in terms of optical wave-packet modes and atomic-ensemble spatial
modes. The output of this process is confirmed to be decomposable into multiple
discrete, bosonic mode pairs, each pair undergoing independent evolution into a
two-mode squeezed state. For this we extend the Bloch-Messiah reduction
theorem, previously known for discrete linear systems (S. L. Braunstein, Phys.
Rev. A, vol. 71, 055801 (2005)). We present typical mode functions in the case
of one-dimensional scattering in an atomic vapor. We find that in the absence
of dispersion, one mode pair dominates the process, leading to a simple
interpretation of entanglement in this continuous-variable system. However,
many mode pairs are excited in the presence of dispersion-induced temporal
walkoff of the Stokes, as witnessed by the photon-count statistics. We also
consider the readout of the stored atomic polarization using the anti-Stokes
scattering process. We prove that the readout process can also be decomposed
into multiple mode pairs, each pair undergoing independent evolution analogous
to a beam-splitter transformation. We show that this process can have unit
efficiency under realistic experimental conditions. The shape of the output
light wave packet can be predicted. In case of unit readout efficiency it
contains only excitations originating from a specified atomic excitation mode.
