  The existence of Weyl nodes in the momentum space is a hallmark of a Weyl
semimetal (WSM). A WSM can be confirmed by observing its Fermi arcs with
separated Weyl nodes. In this paper, we study the spin- orbit interaction of
light on the surface of WSM in the limit that the thickness is ultra-thin and
the incident surface does not support Fermi arc. Our results show that the
spin-dependent splitting induced by the spin-orbit interaction is related to
the separation of Weyl nodes. By proposing an amplification technique called
weak measurements, the distance of the nodes can be precisely determined. This
system may have application in characterizing other parameters of WSM.
