Features of Free Polarization Decay in Ultrathin Gas Cells

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.