  Light-matter interaction is one of the key routes to understanding and
manipulating geometric and electronic behaviors of materials, especially
two-dimensional materials which are optically accessible owing to their high
surface to volume ratio. In the current work we focus on the recently
discovered two-dimensional sliding ferroelectric materials, in which the
out-of-plane electric polarization can be switched with a small horizontal
translation in one layer. Combining symmetry analysis and first-principles
calculations, we predict that light illumination could inject non-equilibrium
magnetic moments into the sliding ferroelectrics. Such magnetic moment is
composed of both spin and orbital degrees of freedom contributions. We use
$\mathrm{ZrI}_2$, $\mathrm{WTe}_2$, and $\mathrm{MoS}_2$ bilayer ferroelectrics
to illustrate our theory. Under intermediate light illumination, one can yield
non-equilibrium magnetic moments on the order of $0.1-1$ $\mu_B$ in these
systems, which also depends on the polarization nature of incident light.
Furthermore, we show that such photo-injected magnetism changes its sign when
the sliding dipole moment switches. This photo-magnetization can be detected by
magneto-optical methods (such as Kerr or Faraday effect), which serves as an
indicator of sliding ferroelectricity. Hence, one can use an all-optical pump
and probe setup to measure and detect the subtle sliding ferroelectric phase.
