Seventh and ninth order nonlinear susceptibility measurement in alkali metal vapour

We report the first experimental measurement and theoretical estimation of seventh _eff ⁽⁷⁾ and ninth _eff ⁽⁹⁾ order effective nonlinear susceptibilities. The correlation of ninth, seventh and fifth harmonic signal efficiencies in various phase-matched mixtures of Ar (or Xe) and sodium atoms, is experimentally investigated. Using direct and cascade processes of harmonic generation, the modulus ratio is measured for the higher nonlinearities, which allows an estimation of _eff ⁽⁷⁾ and _eff ⁽⁹⁾ from the lower order optical susceptibilities. Results from numerical calculations of atomic nonlinear susceptibilities up to the ninth order, accounting for the discrete spectrum and the continuum, are presented.