  Interaction of a strong laser pulse with matter transfers not only energy but
also linear momentum of the photons. Recent experimental advances have made it
possible to detect the small amount of linear momentum delivered to the
photoelectrons in strong-field ionization of atoms. Linear momentum transfer is
a unique signature of the laser-atom interaction beyond its dipolar limit.
Here, we present a decomposition of the subcycle time-resolved linear momentum
transfer in term of its multipolar components. We show that the magnetic dipole
contribution dominates the linear momentum transfer during the dynamical
tunneling process while the post-ionization longitudinal momentum transfer in
the field-driven motion of the electron in the continuum is primarily governed
by the electric quadrupole interaction. Alternatively, exploiting the radiation
gauge, we identify nondipole momentum transfer effects that scale either
linearly or quadratically with the coupling to the laser field. The present
results provide detailed insights into the physical mechanisms underlying the
subcycle linear momentum transfer induced by nondipole effects.
