Chapter 2 - Theoretical approach to the design of organic molecular and polymeric nonlinear optical materials

Abstract

This chapter discusses the theoretical approach to the design of organic molecular and polymeric nonlinear optical (NLO) materials. The focus of the chapter is on the determination of the second- and third-order NLO properties, β and γ, of conjugated organic molecules and polymers in the nonresonant regime. At the macroscopic level, these properties are known as the second- order (x(2)) and third-order (x(3)) susceptibilities. For increasingly large oligomers tending toward the polymeric limit, the system is finite in the transverse and perpendicular directions but effectively infinite along the longitudinal direction. In the latter case, it is convenient to define the hyperpolarizability per unit cell, β/N or γ/N, which, in the infinite chain length limit, is equivalent to the nonlinear susceptibility.