  When a light beam is strongly laterally confined, its field vector spins in a
plane not perpendicular to the propagation direction, leading to the presence
of transverse spin angular momentum, which plays a crucial role in the field of
chiral quantum optics. The existing techniques to measure the transverse spin
density require complex setups and sophisticated time-consuming procedures.
Here, we propose a scheme to measure the transverse spin density of an optical
field in real time using a multi-level atomic medium. The susceptibility of the
medium is spatially modulated by the transverse spin via electromagnetically
induced transparency. The distribution of the transverse spin is then extracted
by measuring the distributions of the Stokes parameters of another collimated
probe field.
