  We consider birefringent (i.e., polarization changing) scattering of x-ray
photons at the superposition of two optical laser beams of ultra-high intensity
and study the resonant contributions of axions or axion-like particles, which
could also be short-lived. Applying the specifications of the Helmholtz
International Beamline for Extreme Fields (HIBEF), we find that this set-up can
be more sensitive than previous light-by-light scattering (birefringence) or
light-shining-through-wall experiments in a certain domain of parameter space.
By changing the pump and probe laser orientations and frequencies, one can even
scan different axion masses.
