  The second-order nonlinear optical coefficients associated with chirality
differ in sign for the two mirror-image forms (enantiomers) of a chiral
material. Structures comprised of alternating stacks of the enantiomers can
therefore be used for quasi-phase-matched frequency conversion, as we
demonstrate here by second-harmonic generation from Langmuir-Blodgett films of
a helicenebisquinone. Such structures could lead to new types of frequency
converters in which both the second-order nonlinear response and
quasi-phase-matching arise from the chirality of a material rather than its
polar order. PACS numbers: 42.65.Ky, 42.70.Nq, 78.66.Qn
