Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
Photorefractive polymeric materials
Abstract
This thesis describes the experimental investigation of photorefractive gratings in polymers. The polymer mixture studied most extensively is a mixture of Bisphenol A 4,4$\sp\prime$-nitroaminostilbene with 29 wt.% benzaldehyde-diphenylhydrazone. We characterized this compound by determining its electrical, optical and electro-optical properties. Two-beam coupling experiments measured the steady state photorefractive grating strength as a function of a number of externally controllable parameters, e.g. applied electric field strength or wavelength. Degenerate four-wave mixing experiments determined the transient photorefractive properties. We found that this photorefractive polymer exhibits much improved grating strength and writing speed compared to earlier polymer mixtures. The two-beam coupling gain coefficient at 650 nm wavelength was as high as 56 cm$\sp{-1}$ and the speed of cm grating erasure was as fast as 0.1 s$\sp{-1}$ at 1 W/cm$\sp2$ intensity. I also investigated the effect of the charge transport agent on grating strength and writing/erasing speed by using different charge transport agents in an otherwise unchanged photorefractive polymer. A modified AC-phase-modulation technique permitted high precision measurements of the photorefractive phase shift. The accuracy of the phase shift was better than 0.5$\sp\circ$ at phase shifts near 90$\sp\circ$. Measurements of the phase shift as a function of applied electric field strength are in good agreement with standard photorefractive theory. I investigated the influence of attenuation on the speed of erasure of photorefractive gratings by solving the coupled-wave equations in the undepleted pump approximation and taking into account the attenuation and the Gaussian intensity profile of all the beams. The extrinsic grating decay rate is significantly lower than the intrinsic photorefractive decay rate in samples with overall attenuation as low as 10%. The Gaussian beam profiles of the readout and erasing beams result in a further reduction of the extrinsic decay rate. The results of these calculations are used to determine the spectrum of intrinsic decay rates in a photorefractive polymer.
Subject Area
Optics|Condensation
Recommended Citation
Liphardt, Martin M, "Photorefractive polymeric materials" (1997). ETD collection for University of Nebraska-Lincoln. AAI9804332.
https://digitalcommons.unl.edu/dissertations/AAI9804332