  We investigate the dynamics of a single two-level atom, which interacts with
pulses propagating in two spatial-modes (right and left) and
frequency-continuum. Using Heisenberg equations of motion, we present the
explicit analytical derivations and general formalisms for atomic excitation
with two spatial-mode multi-photon pulses in both Fock state and coherent
state. Based on those formalisms, we show that perfect atomic excitation by
single photon Fock state pulse can only be realized when it is
rising-exponentially shaped in the even-mode---a balanced superposition of the
two spatial-modes. Single photon from single spatial-mode can only give half of
the maximal atomic excitation probability. We also show that the maximum atomic
excitation probability with multi-photon pulses in the even-mode is a monotonic
function of the average photon number for coherent state, but not for Fock
states. Furthermore, we demonstrate that the atomic dynamics can be controlled
by the relative phase between the two counter-propagating coherent state pulses
incident on the atom, which is not the case with two Fock state pulses.
