First observation of magneto-electric directional anisotropy in a gas
Résumé
We report the first observation of the anisotropy of the velocity of light, induced in a gas by electric and magnetic fields. This bilinear magneto-electro-optical phenomenon appears in the presence of crossed electric and magnetic fields perpendicular to the light wavevector, as a refractive index difference between two counterpropagating directions. Using a high finesse ring cavity, we have measured the magneto-electric directional anisotropy of molecular Nitrogen at ambient temperature and atmospheric pressure to be $2\eta_{\parallel \;{\mathrm{exp}}}(\mathrm{N_2})= (4.7\pm 1)\times 10^{-23}\;\mbox{T}^{-1}\mbox{.V}^{-1}\mbox{.m}$ for $\lambda =1064\;$nm, in agreement with the expected order of magnitude. Our measurement opens the way to a deeper insight into light-matter interaction, since bilinear magneto-electric effects correspond to a coupling beyond the electric dipole approximation. Moreover, the same effect is expected in quantum vacuum.
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