Calculation of the dispersion of the third-order optical nonlinearity in C₆₀ films

Abstract

Using wave functions determined from ground-state local-density calculations, we have calculated the wave-dispersed free response of the optical nonlinear polarizabilityγ ⁽³⁾(−3ω;ω,ω,ω), for the C₆₀ molecule andχ ⁽³⁾(−3ω;ω,ω,ω) i.e. Third-Harmonic Generation (THG) for films using a sum-over-states approach. The influence of screening was determined by applying an external static electric field in separate selfconsistent calculations to evaluate induced dipole moments which was used to determine the static linear and nonlinear polarizabilities. The polarizabilities calculated in the static limit were used to determine an effective screening parameter which was, in turn, used together with an RPA approach to calculate screened wave-dispersed, third-order nonlinear optical properties such asγ ⁽³⁾(−3ω;ω,ω,ω) andχ ⁽³⁾(−3ω;ω,ω,ω). Comparing evaluated polarizabilities with experimental values we found that the non-resonant free polarizability compares well in absolute magnitude with experimental results. Inclusion of screening results in a polarizability about two orders of magnitude below the experimental values.