Absorption and Scattering in Nonlinear Optical Polymeric Systems

Nonlinear organic systems often consist of a polymer matrix with a optical chromophore as a guest or an attached side chain. For enhanced optical nonlinearity, the chromophore absorption band should be located near the desired operating wavelength, but with no absorption. Good optical transmission is critical, and both the absorption and the scattering need to be minimized. Since the films are usually thin and weakly absorbing, it is difficult to determine either of these two material properties. By using the highly sensitive absorption technique of photothermal deflection spectroscopy (PDS), it is possible to obtain the fundamental optical spectrum of the nonlinear optical (NLO) systems over a wide energy range, and separate the absorption from the scattering. With this information, one can then select optimal polymer-chromophore systems. The absorption data indicates what the intrinsic waveguide loss should be for any given wavelength. For materials with low absorption, if there is high waveguide loss, either improved processing is necessary to lower the scattering, or insertion losses need to be reduced.