Second-harmonic generation in nonpolar chiral materials: relationship between molecular and macroscopic properties

Abstract

An oriented gas model for the second-order nonlinear optical response for optical second-harmonic generation in axially aligned nonlinear optical chromophores in chiral media is presented. Design criteria for the alignment of chromophores possessing Kleinman-disallowed traceless symmetric second-rank tensor hyperpolarizabilities β resulting in large nonlinear optical susceptibilities χ(2) are enumerated. These chromophores could be oriented in high-density, highly ordered structures due to the absence of dipolar interactions resulting in exceptionally large χ(2) values. The alignment of chromophores that have C2v or Dn(n>2) symmetry in two chiral nonpolar symmetry groups for the medium, D∞ and D2, are considered. Criteria for response optimization and several physical examples are described. Additionally, certain nonpolar symmetry groups for the medium, of which the most easily realizable is probably D2, also admit Kleinman-allowed octupolar susceptibilities for which the optimum chromophore alignment is discussed.