  The OSQAR photon regeneration experiment searches for pseudoscalar and scalar
axion-like particles by the method of "Light Shining Through a Wall", based on
the assumption that these weakly interacting sub-eV particles couple to two
photons to give rise to quantum oscillations with optical photons in strong
magnetic field. No excess of events has been observed, which constrains the
di-photon coupling strength of both pseudoscalar and scalar particles down to
$5.7 \cdot 10^{-8}$ GeV$^{-1}$ in the massless limit. This result is the most
stringent constraint on the di-photon coupling strength ever achieved in
laboratory experiments.
