Optimizing the second-order nonlinear optical response in some indoline-based chromophores at the molecular and macroscopic levels

ABSTRACT The effect of extending the conjugation length, the deployment of various substituents and configurational locking of the polyene backbone on the second-order nonlinear optical (NLO) response of a series of indoline based compounds has been investigated. The compounds were examined using Hyper-Rayleigh scattering (HRS) and relative second-harmonic generation (SHG) techniques with a femtosecond operating system with a 1300 nm fundamental wavelength. All of the compounds were found to have high molecular hyperpolarizabilities with  values of up to 1230 x 10 -30 esu. At the macroscopic level - for poled polymer thin films - a stro ng second-order NLO signal has been detected and d 33 values of up to 217 pm/V are found – a response of some ten times greater than that found for the well known azo dye Disperse Red 1. Keywords: Second-order nonlinear optics, hyper-Rayleigh scattering, hyperpolarizability, corona poling, indoline and dipolar chromophore 1. INTRODUCTION Among the many known nonlinear optical (NLO) processes, the phenomenon of second-order optical nonlinearity is one of the most well studied. This is because materials with high second-order nonlinearities are expected to underpin applications in areas such as electro-optic switching for telecommunications