  The photon splitting gamma -> gamma gamma in a time-independent and
inhomogeneous magnetized background is considered when neutral and ultralight
spin-0 particles are coupled to two-photons. Depending on the inhomogeneity
scale of the external field, resonant photon splitting can occur. If an optical
laser crosses a magnetic field of few Tesla with typical inhomogeneity scale of
the order of the meter, a potentially observable rate of photon splittings is
expected for the PVLAS range of couplings and masses.
