ABSTRACT
Photoanisotropic materials, in particular azodyes and azopolymers, have attracted significant research interest in the last decades. This is due to their applications in polarization holography and 4G optics, enabling polarization-selective diffractive optical elements with unique properties, including circular polarization beam-splitters, polarization-selective bifocal lenses, and many others. Numerous methods have been applied to increase the photoinduced birefringence of these materials, and as a result, to obtain polarization holographic elements with a high diffraction efficiency. Recently, a new approach has emerged that has been extensively studied by many research groups, namely doping azobenzene-containing materials with nanoparticles with various compositions, sizes, and morphologies. The resulting nanocomposites have shown significant enhancement in their photoanisotropic response, including increased photoinduced birefringence, leading to a higher diffraction efficiency and a larger surface relief modulation in the case of polarization holographic recordings. This review aims to cover the most important achievements in this new but fast-growing field of research and to present an extensive comparative analysis of the result, reported by many research groups during the last two decades. Different hypotheses to explain the mechanism of photoanisotropy enhancement in these nanocomposites are also discussed. Finally, we present our vision for the future development of this scientific field and outline its potential applications in advanced photonics technologies.
ABSTRACT
Polarization-selective diffractive in-line and off-axis lenses are recorded in azopolymer thin films using polarization holography. A simple, yet efficient, and to the best of our knowledge, new method is used to suppress the surface relief grating formation and to improve the polarization properties of the lenses. The in-line lenses are converging for right circularly polarized (RCP) light and diverging for left circularly polarized (LCP) light. Bifocal off-axis lenses are recorded by polarization multiplexing. By rotating the sample at 90° between the exposures, the two focal points of these lenses are located in orthogonal directions O x and O y, so we can refer to these novel lenses as 2D bifocal polarization holographic lenses. The light intensity in their focuses depends on the reconstructing light polarization. According to the recording scheme, they can either reach maximum intensities simultaneously (for LCP or RCP), or alternatively, one of them can be at maximum for LCP, while the other for RCP. These lenses may be used as polarization controllable optical switches, in the field of self-interference incoherent digital holography or for other photonics applications.
ABSTRACT
Notwithstanding the significant optical applicability of PAZO polymer films, there are no accurate data about their optical characteristics. To remedy this shortcoming, in this study three PAZO polymer thin films are characterized, with dissimilar thicknesses, on glass substrates using only one UV/VIS/NIR transmittance spectrum T(λ) per sample and an original hybrid dispersion model (HDM). HDM is based on the Tauc-Lorentz model, the new amorphous dispersion formula, the Tauc-Lorentz-Urbach model of Foldyna and the Tauc-Lorentz-Urbach model of Rodriguez. HDM with two oscillators is employed in characterizations of the PAZO polymer films in the range [300, 2500] nm, whereby the root-mean-square deviation (RMSD) of the fitted transmittance spectrum with respect to T(λ) does not exceed 1.6 × 10-3. Decreasing RMSD by 2.3% to 94.4% is demonstrated by employing HDM compared with the above mentioned four popular dispersion models, for each one of the studied films. HDM is applicable to amorphous films independent of their thickness as well as to cases of non-transparent substrate.
