International audience; Meson photoproduction with polarized photons has proved to be a powerful tool to identify contributions of baryon resonances that are not evident in the differential cross-sections. It provides information that are complementary to those extracted using pion-nucleon scattering data. Extensive results have been produced in the past on beam asymmetries by the Graal collaboration for η and $\pi ^0$ on the proton. New results are now available for the same reactions on the quasi-free neutron and for the K+ photoproduction on the proton. Contributions from hitherto undetected baryon resonances may be important to understand the results.