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The results of investigations of kinetics of photoanisotropy induction and relaxation in polarization-sensitive media with dark relaxation are presented. The model consideration of photoanisotropy in polarization-sensitive media with dark relaxation is presented. The conformation-orientation mechanism of the anisotropy induction in these media is considered. The value of “effective anisotropy” is used for the anisotropy description that allows measurements of photoanisotropy to be made in real-time. The time dependence of the value of photoanisotropy and dark relaxation on the acting radiation intensity and relaxation coefficient is shown. The experimental investigations are carried out on materials on the basis of azodye Dimethyl Yellow introduced into different polymer matrices.

Anisotropic change of the absorbtion edge of seleno-cadmium glass under the action of linearly polarized monoimpulse of a ruby laser of great power has been investigated. The spectral width of the area of anisotropic bleaching of the sample which is being radiated has been estimated. The dispersion curves of photoinduced birefringence and the anisotropy of the absorbtion on the absorbtion edge of the glass of RY-19 type have been obtained in the interval (6500-6700 A).

In this article the results of experimental investigations of photo anisotropy in organic dyes embedded in different polymer matrices are reported. All the matrices used in this work can be subdivided into those entering into a chemical reaction with dye molecules and those that are chemically inactive. The results of this investigation are suggested that the matrix is of crucial importance of the creation of photo anisotropic materials.

Dynamic polarization-holographic gratings with a different profile of anisotropy in the band are presented. Polarization-sensitive recording materials of two types are used: material possessing high dark relaxation and highly reversible material without dark relaxation in which the recorded grating is erased by a circularly polarized beam. For a grating recorded by two orthogonally circularly polarized beams a diffraction efficiency of 20% has been obtained at 3.5 W/cm2 power density during 1 ms recording/erasing time. An all-optical cross commutator based on the matrix of dynamic reprogrammable polarization-holographic microholograms is considered. The amplification of the weak beam at two-wave mixing in polarization-sensitive materials has been shown, with an obtained amplification coefficient of 4.95.

The results of investigations of kinetics of photoanisotropy induction and relaxation in polarization-sensitive media with conformation-orientation mechanism of the anisotropy induction and having significant dark relaxation are presented. It is shown that such materials can be applied for tasks of dynamic polarization holography. With the purpose of improvement dynamic characteristics of polarization-sensitive materials azodye Nitrodimethyl red (NDMR) is specially synthesized. Materials on the basis of NDMR are used for recording dynamic polarization-holographic gratings with different profile of anisotropy. The results of the investigation of kinetics of diffraction efficiency (DE) of these gratings and the analysis of polarization state of diffracted orders are given. It is shown that the time of a cycle of recording/erasing for gratings of some types is of the order of 100 ms at DE = 21%. The theoretical model of dynamic polarization-holographic recording on such materials is presented. Possible applications of the methods of dynamic polarization holography are discussed. 

The results of investigations of kinetics of photoanisotropy induction and relaxation in polarization-sensitive media with conformation-orientation mechanism of the anisotropy induction having significant dark relaxation are presented. It is shown that such materials can be applied for tasks of dynamic polarization holography. With the purpose of improvement dynamic characteristics of polarization-sensitive materials azodye Nitrodimethyl red (NDMR) is specially synthesized. Materials on the basis of NDMR are used for recording dynamic polarization-holographic gratings with different profile of anisotropy. The results of the investigation of kinetics of diffraction efficiency (DE) of these gratings and the analysis of polarization state of diffracted orders are given. It is shown that time of a cycle of recording/erasing for gratings of some types is of the order of 100 ms at DE = 21 %. The theoretical model of dynamic polarizationholographic recording on such materials is presented. Possible applications of the methods of dynamic polarization holography are discussed.

The well-known scalar photochromism phenomenon is a reversible phototransformation of chemical species between two forms having different absorption spectra. It is observed under the action of actinic light regardless of its polarization state. Unlike this in some high-efficient polarization-sensitive azopolymeric materials, we have observed a welldeveloped vector polyphotochromism which appears as a light-induced area with spectral selectivity for the linearly polarized probing beams. A sharp change in the transmission spectrum of the material have been observed when we placed an irradiated area of the sample between crossed polarizers, while the transmission spectrum of the sample remained practically unchanged in case of probing by unpolarized light. The effect has a purely vector nature, while the transmission spectrum of the exposed material essentially changes in case of observing between crossed polarizers and the change in the spectrum unambiguously depends on the energy exposure. A significant dependence of the kinetic of the vector polyphotochromism induction on the power density of linearly polarized actinic light (445 nm) is shown for probing beam of 635 nm. It is also shown that the kinetics of the effect depends on the photosensitive layer thickness and the concentration of the chromophore. The experiments were carried out for two synthesized side-chain azopolymers obtained as immobilized polar azo dyes on polymethylmethacrylate backbone. It is clearly shown a light-controlled spectral selectivity of the sample activated by the various doses of the stimulating radiation. 

This paper presents the experiments on photoanisotropic organic media films based on the composition of the azodye and polymer containing different polyelectrolytes. As a part of an experiment to strengthen the cohesion of the matrix macromolecules, we individually added to the test compositions polyelectrolytes with variations of quantity and with the different nature. The kinetic curves of the inducing photoanisotropy in the polarization-sensitive films are shown. The addition of the electrolyte to this type of materials contributes to an early manifestation of vector polyphotochromic effect at low exposures, which in turn is a sign of improved photoanisotropic properties as this effect appears exclusively in high-performance polarization-sensitive materials. 

The phenomenon of vector photochromism was observed in some high-efficient polarization-sensitive materials depending on the radiant exposure of the inducing linearly polarized actinic light. When radiant exposure exceed certain value specific to each material, a sharp change in the transmission spectrum of the probing linearly polarized nonactinic beam is observed after analyzer. While probing with unpolarized light the transmission spectrum is practically unchanged and does not depend on the magnitude of the radiant exposure. The mechanism of this phenomenon is discussed. The effect is an interference nature and depends on the path difference between the ordinary and extraordinary rays in material with photo-induced anisotropy. It is shown that the kinetics of this effect depends on the photosensitive layer thickness and the concentration of the chromophore.The beams with a wavelength away from the absorption band of the material were used as a probing. It is shown that in this case birefringence has made the main contribution in photoanisotropy. The experiments were carried out for polarization-sensitive materials with varying degrees of components integration, in particular, two synthesized side-chain azopolymers obtained by immobilization of polar azo dyes on polymethylmethacrylate backbone. It is shown that the maximum value of the birefringence Δn = 0.162 achieved in azopolymers with covalently bonded components. In this case a third order of interference of the probing beam is observed.

According to our studies of polarization-sensitive materials based on azochromophores and polymers in recent years, a factor significantly influencing their photoanisotropic properties has been revealed. The degree of molecular integration of the material components (light-absorbing centers and polymer matrix) is in direct connection with the level of achievable birefringence in media obtained on their basis. This paper considers the results of a study of the integration of polarization-sensitive materials by means of molecular electrostatic forces. Experimental data of the photoanisotropic behavior of optical media based on advisedly designed organic chromophore salts with the participation of almost all alkali metals are shown. Lithium (Li⁺), sodium (Na⁺), potassium (K⁺), cesium (Cs⁺) and hydrogen (H⁺) are used as cations for these polarized light-receiver organic salts, and as an anion, on the other hand, is a residue of functional monoazo dye. The obtained light-absorbing organic salts are doped into the hydrophilic polymer matrix having good lyophilic compatibility. To study the induction of photoanisotropy in the obtained photosensitive materials, we investigate the effect of actinic polarized light on them with wavelengths of 445 nm and 532 nm and variation of reading wavelengths (at 532 nm and 635 nm) depending on the spectral characteristics of the test samples. Optimum parameters of exposure for each composition are determined experimentally. The kinetic curves of the induction of photoanisotropy in the new comparing polarization-sensitive media are shown as light-induced effective photoanisotropy for the various illumination conditions. 

The paper presents the study of the polarization-sensitive materials developed by us. It is demonstrated the advantages of these light-recording organic media composed both via covalent bindings and through electrostatic interactions.

Shaping the intensity profile of a laser beam is desired by various industrial applications. In this paper, a new approach is presented to design and fabricate liquid crystal (LC) micro-optical elements (MOEs) with engineered Pancharatnam–Berry (PB) phases for beam shaping. By generalizing the Snell's law for spatially variant PB phases, molecular orientation patterns are designed for the liquid crystal MOEs to shape a Gaussian laser beam into flattop intensity profiles with circular and square cross-sections, with the β parameter varied from 4 to 42. It is demonstrated that such liquid crystal beam shaping MOEs can be fabricated with high throughput and high resolution by using a photopatterning technique based on plasmonic metamasks and that they produce excellent beam quality, no zero-order light leakage with a beam size from 10 to 600 µm. As the plasmonic metamasks allow for encoding arbitrary molecular orientations, i.e., arbitrary geometric phase profiles, the approaches presented here are widely applicable to large-scale manufacturing of liquid crystal MOEs for any beam shapes

It is known that polarization holography uses photoanisotropic materials to record the state of light polarization. The polarization-holographic method of storage, transformation, transmission and processing of information is one of the most promising directions not only in optical but also in general among information technologies. The potential of increasing sensitivity of certain types of materials to light polarization is not yet fully mastered. In this paper, azodyecontaining photoanisotropic polymers are represented as a result of the study of polarization-sensitive materials, which are distinguished from their predecessors by outstanding photosensitivity. The report shows results of improving the foreground photoanisotropic characteristics, such as: increasing the degree of light-inducible birefringence and the rate of acceleration of this process. Which is the main measuring criterion of photosensitivity and effectiveness of the studied materials. The efficiency of azodye based polarization-sensitive materials is based on integration of their components by forces of electrostatic interactions or covalent bonds. In our previous works we have repeatedly shown clearly all the advantages of the results achieved by the molecular electrostatic integration of the material components. The presented paper shows different advantages of photoanisotropic materials consisting of alternative, covalent bonds, from which the increased velocity of photoanisotrophy and significantly improved magnitude of photosensitivity are worth noting on the first hand. Based on the experiences accumulated as a result of the conducted recent research and the developed recommendations, the new polarization-sensitive materials have deliberately been synthesized and studied. 

Arrays of living tissue-forming cells behave as orientationally ordered active nematics and create topological defects of strength +1/2 and -1/2. These defects play an important role in compressive-dilative stresses in tissues and facilitate effects such as apoptosis and cell migration. The challenge is to design orientational patterns of cells with predetermined spatial locations of topological defects in them. We propose an approach to control the alignment of human dermal fibroblast (HDF) cells by substrates with photoaligned liquid crystal polymers (LCPs). With a plasmonic metamask alignment method, we patterned the director orientation of the LCPs with topological defects of integer (+1, -1) and semi-integer (+1/2, -1/2) strength. Combination of polarized, phase contrast and fluorescent microscopies proves that the HDF cells align along the patterned director of the LCP substrate. The patterns cause a modulation of cell density, as the cells accumulate near the cores of the defects with positive topological charge. The approach could be used to control the locations of defect formation in tissues of living cells and potentially control the extrusion of undesirable cells.

Liquid crystal elastomers (LCEs) hold a major promise as a versatile material platform for smart soft coatings since their orientational order can be predesigned to program a desired dynamic profile. In this work, we introduce temperature-responsive dynamic coatings based on LCEs with arrays of singular defects-disclinations that run parallel to the surface. The disclinations form in response to antagonistic patterns of the molecular orientation at the top and bottom surfaces, imposed by the plasmonic mask photoalignment. Upon heating, an initially flat LCE coating develops linear microchannels located above each disclination. The stimulus that causes a non-flat profile of LCE coatings upon heating is the activation force induced by the gradients of molecular orientation around disclinations. To describe the formation of microchannels and their thermal response, we adopt a Frank–Oseen model of disclinations in a patterned director field and propose a linear elasticity theory to connect the complex spatially varying molecular orientation to the displacements of the LCE. The thermo-responsive surface profiles predicted by the theory and by the finite element modeling are in good agreement with the experimental data; in particular, higher gradients of molecular orientation produce a stronger modulation of the coating profile. The elastic theory and the finite element simulations allow us to estimate the material parameter that characterizes the elastomer coating's response to the thermal activation. The disclination-containing LCEs show potential as soft dynamic coatings with a predesigned responsive surface profile

Controlled placement of microparticles is of prime importance in production of microscale superstructures. In this work we demonstrate the remote control of microparticle placement using a photo-activated surface profile of a liquid crystal elastomer (LCE) coating. We employ light-responsive LCEs with pre-imposed patterns of molecular orientation (director) in the plane of coating. Upon UV illumination, these in-plane director distortions translate into deterministic topographic change of the LCE coating. Microparticles placed at the interface between the LCE coating and water, guided by gravity, gather at the bottom of photoinduced troughs. The effect is reversible: when the substrates are irradiated with a visible light, the coatings become flat and the colloidal arrays disorganize again. The proposed non-contact manipulation of particles by a photo-activated LCEs may be useful in development of drug delivery or tissue engineering applications.

In this paper, we aim to show that liquid crystal films (LCs) with well-defined molecular orientations are an exceptional platform for flat optical devices based on the Pancharatnam-Berry (PB) phase. Especially, the development of plasmonic photopatterning technique in recent years has made it easy to align liquid crystal molecules in to designer orientation patterns with both high spatial resolution and high throughput and thus enables large scale manufacturing liquid crystal optical devices with low costs. Here we present liquid crystal laser beam shapers and microlenses as two examples to illustrate the design principles and the fabrication processes for liquid crystal flat optical elements. In comparison with flat optical devices made of plasmonic or dielectric metasurfaces, liquid crystal flat optical elements are advantageous due to the high optical efficiencies and low fabrication costs.

The paper presents the results of a study comparing polarization-sensitive media based on polar hydrophilic polymers with oppositely charged and similarly charged macromolecules.

We report the preparation of a new light-responsive side-chain terpolymer containing azobenzenes, as chromophoric components, sulfonic groups, as polar components, and methacrylate groups, as film forming components, and we provide a detailed characterisation of its thermal parameters, photoanisotropic character, dielectric response and optoelectronic properties. The poly[(4-methoxyazobenzene -4′-oxy) methacrylate]-co-poly[2-acrylamido-2-methyl-1-propanesulfonic acid]-co-poly[methyl methacrylate], MeOAzB/AMPS/MMA, was prepared by radical copolymerisation, possesses high thermal stability and is amorphous. Its high glass transition (T_g = 151 °C) is explained by steric effects (induced by the bulky azobenzenes) and hydrogen bonding (promoted by the polar sulfonic groups) near the polymeric backbone, which may also reduce the photoanisotropic efficiency. The transition between the energy levels of the azobenzenes (MeOAzB) in the terpolymer is controlled by p-type conductivity, and can be associated to motions in the side-chains containing the sulfonic groups (AMPS), which are locally activated below the MeOAzB/AMPS/MMA glass transition.

Active systems composed of self-propelled units show fascinating transitions from Brownian-like dynamics to collective coherent motion. Swirling of swimming bacteria is a spectacular example. This study demonstrates that a nematic liquid crystal environment patterned as a spiral vortex controls individual-to-collective transition in bacterial swirls and defines whether they expand or shrink. In dilute dispersions, the bacteria swim along open spiral trajectories, following the preimposed molecular orientation. The trajectories are nonpolar. As their concentration exceeds some threshold, the bacteria condense into unipolar circular swirls resembling stable limit cycles. This collective circular motion is controlled by the spiral angle that defines the splay-to-bend ratio of the background director. Vortices with dominating splay shrink the swirls toward the center, while vortices with dominating bend expand them to the periphery. Spiraling vortices of 45∘ with splay-bend parity produce the most stable swirls. All the dynamic scenarios are explained by hydrodynamic interactions of bacteria mediated by the patterned passive nematic environment and by the coupling between the concentration and orientation. The acquired knowledge of how to control individual and collective motion of microswimmers by a nematic environment can help in the development of microscopic mechanical systems.

The phenomenon of vector polyphotochromism was found earlier in some high-efficient polarization-sensitive materials depending on the radiant exposure of the inducing linearly polarized actinic light. This effect was observed at high radiant exposures. In this paper the vector polyphotochromic effect is considered when azimuthally dependent exposure is used. The principal difference in these two approaches is that, in exposure-dependent technique, the transmission spectrum of the material depends on the magnitude of the inducing light exposure and this dependence is non-linear. Therefore, certain tunable spectral profiles of the material are very difficult to be fixed, in particular, in the blue spectral region. In the use of the azimuthally dependent technique, the changes in the transmission spectrum are occurred depending on the polarization azimuth of the inducing light. It is shown that the advantage of this approach is the possibility of inducing this effect at much lower exposures of the exciting radiation and obtaining approximately linear dependence of the spectral characteristics of the material on illumination conditions. It should be noted the material used exhibits photochromic behavior of an unusual nature, which is based not on a slight change in the spectral characteristics of the pigment under the light action, but there are changes in the so-called interference color of the medium as a result of selective quenching the corresponding regions of the transmission spectrum of the given material. The polarizationsensitive materials based on biopolymer matrix and organic azo dyes have been used. The obtained results can be used for creating spectral-selective polarization element with high-speed.

The paper outlines the capabilities of color recording of monochromatic polarized light using the phenomenon of vector polyphotochromism. This effect was revealed within the framework of research and development of organic polarization-sensitive media conducted by us.

Polarization-sensitive media based on polymers and functional chromophores have deservedly occupied their niche among photonic materials that are increasingly contributing to the possibilities of richer light sensing, in the field of optical communications, information transfer, its storage, display, etc. within a wide range of applications. The media considered here are represented by multiple highly polar compositions based on functional azo dyes doped in a compatible biopolymer as a matrix. This paper presents our specific studies on the influence of molecular-structural factors on the photoanisotropic properties of polarization-sensitive compositions. The illustrative examples show evidence of the finding of one of the factors that work out the light sensitivity of the materials for multiple times. This factor was the molecular aggregation of the chromophoric component. Quite accurate comparisons are shown of the improvement in photoresponsibility of various compositions with the mutual combination of their chromophoric molecules, in particular as a result of their component dimerization. In the overwhelming majority of azochromophoric dimers demonstrate greater sensitivity to actinic polarized light rather than their predecessor versions. The paper also demonstrates an example of going beyond the framework of dimerization towards the further development of the aggregation of molecules with the formation of azopolymers. The latter turned out to be promising in the case of the correct implementation of increasing integration of the components of the studied materials.