CHROMOPHORES FOR 2ND-ORDER NONLINEAR OPTIC MATERIALS

The theory of the electro-optic effect and second harmonic generation is developed in the context of the linear Stark effect. This leads to an emphasis both on the optical bandwidth of the charge-transfer trans itions responsible for the hyperpolarisability, and on the relationshi p between the transition energies and optical frequency of an electro- optic device. A simple treatment of vibronic coupling illustrates the connection between the bond-length alternation in conjugated polyenes and the sign and magnitude of the non-linearity. A brief survey is mad e of current chemical strategies for optimising the non-linearity.