Inversionless light amplification in sodium

Abstract Light amplification without population inversion in sodium vapor is reported. The result of this work is the amplification of a weak probe beam at a wavelength of 589.0 nm when the atoms are driven coherently by a long pulse at 589.6 nm, and the amplification of a weak probe beam at 589.6 nm when the atoms are driven coherently at 589.0 nm. The population contributions in the upper and lower lasing levels are calculated through the absorption spectra.