Axion production by electromagnetic fields

By consideration of the conversion of photons into axions in the presence of a classical background magnetic field, the possibility of creating artificial sources of ‘‘invisible’’ axions with a laboratory experiment is stressed. With, in particular, a high-power laser, the attainable axion current density seems to be as high as that expected from the natural astrophysical sources, provided that the axion mass is not much larger than ${10}^{\mathrm{-}5}$ eV.