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 <i>β</i> resulting in large nonlinear optical susceptibilities <i><sub>X</sub></i><sup>(2)</sup> are enumerated. These chromophores could be oriented in high-density, highly ordered structures due to the absence of dipolar interactions resulting in exceptionally large <i><sub>X</sub></i><sup>(2)</sup> values. The alignment of chromophores that have <i>C</i><sub>2<i>v</i></sub> or <i>D<sub>n</sub></i> (<i>n</i> greater than 2) symmetry in two chiral nonpolar symmetry groups for the medium, <i>D</i><sub>∞</sub> and <i>D</i><sub>2</sub>, 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 <i>D</i><sub>2</sub>, also admit Kleinman-allowed octupolar susceptibilities for which the optimum chromophore alignment is discussed.
© 2001 Optical Society of America