Higher diffraction order images in photorefractive liquid crystal polymer composite

About forty years ago, Ashkin found that the refractive index was changed when laser transmits some materials¹, then photorefractive(PR) phenomenon was found. During the past four decades, photorefractive nonlinear optics has received great attention due to its real-time operation, high sensitivity, and high holographic storage capacity^2,3. The interbeam angle between signal and reference beam usually is large than ten degrees when people storage information, so we can use fundamental photorefractive grating and avoid the influence of higher-order diffraction. However, higher-order diffraction can be used to realize image processing. It has not been well studied because higher-order diffraction images are usually blurry for crystal. With research expanding, photorefractive polymer materials are being paid much attention because of the properties of easy processing, fast response and material flexibility⁴. In this paper, we firstly report some novel photorefractive higher-order diffraction phenomena of polymer material (PVK:5CB:C₆₀ )at small interbeam angle. The photorefractive composite consists of polymer poly[N-vinylcarbazole](PVK)doped with 4, 4 - n - pentylcyanobiphenyl (5CB) and C₆₀. The weight ratio is 55.45%:44.45%:0.10%(PVK:5CB:C₆₀). The higher-order diffraction images are clear. The experiments testify the feasibility of optical image processing. In two-wave coupling experiments, signal beam is interfered with a mutually coherent reference beam within composites. Results are given respectively when signal beam was focused behind the composites, in front of the composites, in the composites. Higher diffraction order images are amplificatory or inverse. A theory of higher diffraction order images properties in photorefractive liquid crystal polymer composites has been developed. The theory is in good agreement with experimental work.