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Second order nonlinear optical properties of organic molecules and polymeric thin films for photonics applications
Abstract
Aspects related to the magnitude and stability of the nonlinear response of organic nonlinear optical materials are examined. The first hyperpolarizabilities, $\beta,$ of donor-acceptor substituted heterocyclic compounds are measured by second-order, hyper-Rayleigh scattering using an excitation wavelength of 1064 nm. The use of an external standard in the determinations is compared with the use of an internal standard. The effects of molecular interactions on the concentration dependence of the hyper-Rayleigh scattering signal is discussed. Hyper-Rayleigh scattering measurements are also performed on a series of heterocyclic compounds using an excitation wavelength of 1907 nm. This wavelength is the longest that has yet been reported for the hyper-Rayleigh scattering experiment and allows measurements of the first hyperpolarizability of chromophores that are free of contributions from two-photon absorption induced fluorescence and reduces one and two photon resonance enhancement to a minimum. The equipment and procedures used to make measurements at this wavelength is described in detail. The behavior of surface and trapped charge that originate during contact electric-field poling of a model guest-host nonlinearly active polymer is investigated in three different systems. The poling current present in a fresh sample is found to differ in both magnitude and temporal dependence to that observed in the sample during subsequent polings. The magnitude of the steady-state current eventually reached during the poling process is found to depend on temperature and is related to the mobility of charge. A sharp drop-off in SHG signal intensity that occurs when the poling electrodes are grounded is shown to result from the removal of surface charge that orients chromophore dipoles near the surface of the film. The build-up of trapped charge explains a memory effect in which the SHG signal relaxation time gradually increases as the film is subjected to multiple polings until a steady-state value is reached. Finally, it is demonstrated that the charges trapped in the polymer matrix are released only after the polymer is heated to high above its glass transition temperature.
Subject Area
Chemistry|Optics
Recommended Citation
Pauley, Mark Allan, "Second order nonlinear optical properties of organic molecules and polymeric thin films for photonics applications" (1998). ETD collection for University of Nebraska-Lincoln. AAI9838601.
https://digitalcommons.unl.edu/dissertations/AAI9838601