Three-Photon Magnetoabsorption of Excitons in Alkali Halides

Three-photon magnetoabsorption measurements in fields up to 9 T are presented for the first time. A narrow exciton line of ${\Gamma }_5^{-}$ symmetry is resolved in CsI at 5.8076 eV. A $g$ value of 1.17 is deduced from the Zeeman splitting of this exciton. At high magnetic fields an exciton of ${\Gamma }_3^{-}$ symmetry is detected. The analysis of the field-dependent mixing of the ${\Gamma }_3^{-}$ and ${\Gamma }_5^{-}$ excitons yields a zero-field shift of the ${\Gamma }_3^{-}$ exciton to lower energies of 0.54 meV and an effective $g$ value for the admixture of 1.20.