Abstract
Dynamic near-field scanning optical microscopy (NSOM) and asymmetric two-beam coupling experiments are performed on thin films of photorefractive polymer-dispersed liquid crystals (PDLCs). Results obtained from films doped with perylene (serving as the photoexcitable electron donor) and N,N‘-dioctyl-1,4,5,8-naphthalene diimide (NDI) (the electron acceptor) are compared to those obtained from films that have also been doped with tetrabutylammonium tetrafluoroborate (TBATFB). Both the dynamic NSOM and two-beam coupling results provide clear evidence for enhanced photorefractivity in films doped with permanent ions such as TBATFB. Computer simulations of the NSOM results lend supporting evidence and also provide valuable information on the origins of this enhancement. It is concluded that the enhanced optical response arises from the nonlinear dependence of the liquid crystal orientation state on the electric fields within individual liquid crystal droplets and, hence, the concentrations of both permanent and photogenerated ions. These observations suggest a possible alternative means for enhancing the response of photorefractive devices employing dye-doped polymer-dispersed liquid crystals.
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