Abstract The optical effect of free polarization decay in an ultrathin gas cell the inner thickness of which is less than or of the order of the wavelength of the exciting monochromatic laser pulse transmitted orthogonally to plane-parallel walls of this cell is studied theoretically. A new mechanism of the studied effect is established; it is caused by the specificity of phase mismatch of light-induced atomic dipole moments due to transit-time relaxation of atoms in such a cell. As a result, the dynamics of free polarization decay in the considered situation radically differs from the known case in a usual (macroscopic) gas cell. Nontrivial oscillatory dependences of free polarization decay signals on the ratio of the thickness of such ultrathin cell to the radiation wavelength of the exciting pulse are revealed and analyzed.
The interaction of elliptically polarized radiation with a resonant medium consisting of atoms with an excited state split into a doublet was studied theoretically. Interference terms associated with the coherent interaction of the field with the excited sublevels of the doublet were found to appear in the refractive index. The dispersion dependence of the refractive index was studied. It was shown that the decay constants for the multipole moments of the current of a dipole-forbidden atomic transition can be determined by the choice of the wave polarization.