Tunable Polarization and Surface Relief Holographic Gratings in Azopolymer Nanocomposites with Incorporated Goethite (α-FeOOH) Nanorods

Density Functional Theory Prediction of Laser Dyes-Cucurbit[7]uril Binding Affinities

Among a variety of diverse host molecules distinguished by specific characteristics, the cucurbit[n]uril (CB) family stands out, being widely known for the attractive properties of its representatives along with their increasingly expanding area of applications. The presented herewith density functional theory (DFT)-based study is inspired by some recent studies exploring CBs as a key component in multifunctional hydrogels with applications in materials science, thus considering CB-assisted supramolecular polymeric hydrogels (CB-SPHs), a new class of 3D cross-linked polymer materials. The research systematically investigates the inclusion process between the most applied representative of the cavitand family CB[7] and a series of laser dye molecules as guests, as well as the possible encapsulation of a model side chain from the photoanisotropic polymer PAZO and its sodium-containing salt. The obtained results shed light on the most significant factors that play a key role in the recognition process, such as binding mode, charge, and dielectric constant of the solvent. The observed findings provide valuable insights at a molecular level for the design of dye-CB[7] systems in various environments, with potential applications in intriguing and prosperous fields like photonics and material science.

Structured polarized laser beams for controlled spiral-shaped mass transfer in azopolymer thin films

We present an approach for the realization of controlled spiral-shaped mass transfer in azopolymer thin films and the fabrication of spiral microreliefs. For such laser processing, we propose to use light fields with structured polarization distributions generated by a transmissive spatial light modulator. The projection lithography approach is utilized, transferring the pattern directly to the surface of azopolymer thin films. The shaped polarization distributions with different dependencies of the polarization vector orientation on the azimuthal angle allow us to drive surface waves on the sample along a spiral trajectory. Additionally, the ability to control the concavity of the formed microreliefs is demonstrated. This approach can be effectively modified for the direct laser fabrication of more complex nano-/micro-elements as well as their arrays.

Nanocomposite Photoanisotropic Materials for Applications in Polarization Holography and Photonics

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.

In-line and off-axis polarization-selective holographic lenses recorded in azopolymer thin films via polarization holography and polarization multiplexing

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.

Blending Approach Preparation of PVA-g-PMA Films with Embedded "Green" Synthesized Silver Nanoparticles for Acetone Optical Detection

The blending approach (also known as the ex-situ approach) was used for the deposition of thin composite films comprising poly(vinyl alcohol-graft-methyl acrylate) (PVA-g-PMA) and silver nanoparticles (AgNPs). Firstly, the copolymer aqueous dispersion was synthesized through the redox polymerization of methyl acrylate (MA) on poly(vinyl alcohol) (PVA) using ammonium cerium (IV) nitrate as the initiator. Then, AgNPs were synthesized through a "green" method using the water extract of lavender based on by-products of the essential oil industry, and then they were blended with the polymer. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to determine nanoparticle size, along with their stability over time in suspension, during the 30-day period. Thin films of the PVA-g-PMA copolymer, with different AgNP volume fractions varying between 0.008 and 0.260%, were deposited via the spin-coating method on Si substrates, and their optical properties were explored. UV-VIS-NIR spectroscopy and non-linear curve fitting were used for the determination of the refractive index, extinction coefficient, and thickness of the films, while photoluminescence measurements at room temperature were conducted for studying the emission of the films. The concentration dependence of film thickness was observed and showed that thickness increased linearly from 31 nm to 75 nm when the nanoparticles' weight content increased from 0.3 wt% to 2.3 wt%. The sensing properties toward acetone vapors were tested in a controlled atmosphere by measuring reflectance spectra before and during exposure to the analyte molecules in the same film spot; the swelling degree of films was calculated and compared to the corresponding undoped samples. It was shown that the concentration of AgNPs of 1.2 wt% in the films is optimal for the enhancement of the sensing response toward acetone. The influence of AgNPs on the films' properties was revealed and discussed.

Hybrid Dispersion Model Characterization of PAZO Azopolymer Thin Films over the Entire Transmittance Spectrum Measured in the UV/VIS/NIR Spectral Region

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.

Efficient Photo-Response of Azobenzene-based Compounds for Holographic Recording

One of the challenges for azobenzene-based materials in fabricating rewritable surface relief gratings is the long response time in the procedure of holographic recording, making it inefficient in real-time applications. In this study, a small molecule azobenzene compound with a facile fabrication route is presented. By a total recording intensity of 200 mW/cm2, a surface relief grating with the modulation depth of 758 nm can be formed in 5 min. The ±1st order diffraction was observed immediately after the holographic recording, and the ±2nd order diffraction was produced in two seconds. Such a short response time makes it possible for use in real-time applications.