  In light-pulsed atom interferometry, the phase accumulated by atoms depends
on the effective wave vector of the absorbed photons. In this work, we proposed
a theory model to analyses the effective wave vector of photons in structured
light. As for monochromatic optical field, a transverse confinement could lead
to diffraction. We put forward that in light-atom interaction, the atom wave
function could also provide a transverse confinement thus affect the effective
wave vector of the absorbed photons. We calculated the relative shift of the
photon effective wave vector when an atom with a Gaussian wave function absorbs
one photon at the waist in a Gaussian beam. This shift could lead to a
systematic effect related to atom spatial distribution in high precision
experiment based on light-pulsed atom interferometry.
