Abstract

The large, ultrafast, nonresonant nonlinear optical responses of conjugated organic molecular structures are now well understood as a result of model calculations¹ and key experiments.² For second-order optical materials, both positive and negative β_ijk (−ω₃;ω₁ω₂) responses in the zero-frequency limit are common. In contrast, for third-order optical materials, negative γ_ijkl (−ω₄;ω₁, ω₂, ω₃) responses in the zero-frequency limit are rare. In this study we report our theoretical results of quantum many-body calculations on a novel type of conjugated structure, squaraines. We show that indeed squaraines possess negative third-order optical properties in the zero- frequency limit, a result that has experimentally been observed by Dirk and his co-workers.³

© 1993 Optical Society of America