Incoherent-to-coherent image converter based on hybrid liquid crystal - photoconducting polymer structure

It has been shown that the layer of nematic liquid crystal, when situated between a pair of transparent electrodes and a polymeric photoconducting layer, can serve as an efficient real-time holographic recording medium. The mutual action of DC biasing field and a space charge field generated by a spatially modulated incoming light in a photoconducting polymer is able to produce respective refractive index modulation in the liquid crystal due to molecular reorientation process. In this work, we demonstrate how, using a non-degenerate three-wave mixing technique, an optical image superimposed on one laser beam (Argon ion laser, lambda = 514 nm) can be transferred to another laser beam (frequency doubled Nd:YAG, lambda = 532 nm). The two laser light sources are mutually incoherent. Such a transfer is possible when both excitation light wavelengths are capable of charge carrier photogeneration process in photoconducting polymer (here, we used a 100-nm thick layer of copolymer of 3-octylthiophene and DR1-substituted thiophene). We report measurements of diffraction efficiency for the system studied in a function of an applied voltage and a light intensity of the incident beams. (C) 2000 Elsevier Science S.A. All rights reserved.