The dependence of complex refractive index for four-level atom on radiation frequencies

The spectral analysis of refractive index for four-level configuration is done for dye molecules with a Gaussian form of coincident mirror-symmetric absorption and emission bands in both principal singlet⿿singlet and excited triplet⿿triplet channels. The optimum values of extinction coefficient in both channels are achieved at frequency tuning near the center of absorption band for each channel. The radiation frequencies in principal η12 ⿿ ±2 and in excited ⿿1 < η34 < 1 channels are required to achieve the extreme values of refractive index in principal channel. The extreme values of refractive index in excited channel occur at frequencies ⿿1 < η12 < 1 and η34 ⿿ ±1.4.