  We demonstrate both theoretically and experimentally beam-dependent photonic
spin-orbit coupling in a two-wave mixing process described by an equivalent of
the Pauli equation in quantum mechanics. The considered structured light in the
system is comprising a superposition of two orthogonal spin-orbit-coupled
states defined as spin up and spin down equivalents. The spin-orbit coupling is
manifested by prominent pseudo spin precession as well as
spin-transport-induced orbital angular momentum generation in a photonic
crystal film of wavelength thickness. The coupling effect is significantly
enhanced by using a deep-subwavelength carrier envelope, different from
previous studies which depend on materials. The beam-dependent coupling effect
can find intriguing applications; for instance, it is used in precisely
measuring variation of light with spatial resolution up to 15 nm.
