Large Third Order Nonlinear Optical Susceptibilities in Organic Materials

Abstract

In order to realize certain ultrafast optical signal processing and logic concepts, materials are needed with both a large and fast responding (in times less than a picosecond) third-order nonlinear optical susceptibility x⁽³⁾ [1,2]. The speed of the nonlinear process is typically attained by using non-resonant excitation [1]. Further. one must be able to obtain the material in the form required for the anticipated application, e.g. waveguides [2,3] or etalons [1] with acceptable linear optical losses. Organic materials may be well suited for such signal processing schemes for several reasons. Firstly, the concept of declocalized electronic wavefunctions for one-dimensional organic systems has lead to the realization of extremely large nonresonant values of the molecular third — order hyperpolarizability [4]. This concept was extended to the solid state resulting in a large nonresonant x⁽³⁾ for the organic polymeric family the polydiacetylenes (PDAs) [5]. Secondly, a large number of polydiacetylenes can be synthesized, and a wide variety of material forms(e.g. single crystals, liquid crystals, and multilayers) are available. In the following we will describe recent progress in the interdisciplinary research being carried out in our laboratory aimed at ultilizing the PDA’s for these signal processing applications.