Irakli Chaganava

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.

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.

The phenomenon of vector polyphotochromism was found earlier in some high-efficient polymeric polarization-sensitive materials depending on the radiant exposure of the inducing linearly polarized light. This effect have been considered when the changes in the material transmission spectrum are occurred depending on the polarization azimuth of the inducing light [1-6]. The effect exhibits a clear selective transmitance that can be tuned by an external optical signal. It is shown the possibility of obtaining approximately linear dependence of the spectral characteristics of the material on exposure conditions. It is assumed that the changes in so-called interference color of the medium occurs as a result of selective quenching in the corresponding regions of the transmission spectrum. ABSTRACT Keywords: vector polyphotochromism, interference color, nature of photoanisotropy, azo dye, biopolymer, organic photonic material, polarization spectroscopy, polarization sensiti+W10ve media, light transmission control

Microswimmers exhibit collective behavior that can be controlled by an anisotropic environment such as a lyotropic chromonic liquid crystal. We explore the effect of splay and bend of the director field on the individual and collective behavior of motile Bacilli subtilis. The director field, imposed through photoalignment, is designed in the form of vortices of topological charge +1. Their geometry changes from pure radial to spiral and to the circular, representing thus deformations of a pure splay, splay-bend mix, and pure bend, respectively. In dilute dispersions, the bacteria follow the pre-imposed director field, but after their concentration reaches some threshold, they engage in a collective unipolar circulation. This collective behavior is controlled by the splay-to-bend ratio: vortices with dominating splay condense the bacterial swarms towards the center, while vortices with dominating bend push them away to the periphery. Vortices with splay-bend parity formed by 45-degree spiraling director produce the most stable swarming with a time-independent radius as long as the bacterial activity is constant. The change in swimming scenario as a function of splay-to-bend ratio is reminiscent of an unstable limit cycle.

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

In the process of research of polarization-sensitive media the photoanisotropic materials based on polar components showed to very good advantage. Among which the most effective were hydrophilic compositions [1]. Most often, water-soluble compounds are represented by molecules with an extreme degree of polarization (organic salts of azo dyes, polyelectrolytes) [2-3] while they generally demonstrate the greatest efficiency in comparison with their hydrophobic analogues and among those listed above the use of a collagen-based matrix was particularly beneficial.

As known, collagen structures are polyampholyte. For these practical tasks we use gelatin. This biogenic substance (GEL) is known for the simultaneous presence of unlike charges in the composition of its macromolecules. In contrast to them, we also investigate the application of a synthetic hydrophilic polymer with only like charges. Among the data on the applications of polarization-sensitive media involved in this study, it should be noted that we use them to create optical elements that are the main part of the device developed by us on optical pattern recognition [4].

In our laboratory, we thoroughly study the photoanisotropic properties of polarization-sensitive media based on organic materials. This paper presents the result of the observation of separately taken two materials that have a great similarity, but which also have isolated substantial differences, due to which the materials under study exhibit different properties. In this way, we obtain valuable information in the cause-effect relationship of the effect induction. This work carries the fundamental value of identifying the influence of structural factors on the photoanisotropic properties of organic polarization-sensitive media obtained on the basis of polymers and functional azo-dyes.

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 study of the mechanism of the phenomenon of vector polyphotochromism led to the opinion that it has an interference nature. This paper presents the first experimental data on the correspondence of this effect with the manifestation of the photoelasticity of the polymer component of the material. We verified the accordance of the transmission spectra of polarized light on the one hand of a photoactivated polarization-sensitive material and on the other hand under the influence of a mechanical stress. The profiles of the obtained polarization spectra match each other.

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.

Topological defects in liquid crystal elastomers (LCE) drive complex stimuli-responsive deformation. Previous studies examined short disclinations oriented parallel to the surface normal of a thin film or coating [1-3]. Here we examine an array of parallel extended disclinations oriented in-plane in an LCE coating on a rigid substrate, produced by forming the LCE between substrates with prescribed anchoring [4]. On heating, the coating morphs to form an array of parallel microchannels, each located above a disclination. To understand this shape evolution, we model formation of disclinations via numerical minimization of the Frank free energy, then use finite element simulation to calculate thermo-responsive deformation. Results are compared with experiments and with analytical calculations in the small-strain limit. We demonstrate use of thermo-responsive microchannels to perform particle sorting. Future uses may include applications in microfluidics and tissue engineering. [1] McConney et al, Adv Mater 25, 5880 (2013); [2] Babakhanova et al Nat Commun 9, 456 (2018); [3] Konya et al, Front Mater 3, 24 (2016); [4] Wang et al Nat Commun 8, 388 (2017).

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.

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

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.

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 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.

Phenomenon of vector polyphotochromism was observed in some high-efficient polarization-sensitive materials dependent on the radiant exposure when material was illuminated with linearly polarized actinic light. The phenomenon has purely vector nature.                                                         

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 Dn = 0.162 achieved in azopolymers with covalently bonded components. In this case a third order of interference of the probing beam is observed

The phenomenon of vector polyphotochromism within a wide spectral range is revealed in organic polarization-sensitive materials when material is illuminated with linearly polarized actinic 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 degree of integration of the component molecules of the material by the cohesion of both ways the electrostatic forces (by use mineral electrolytes and polyelectrolytes) and the covalent bonds (azopolymers based on different chromophores), as well as on the photosensitive layer thickness and the concentration of the chromophore. The mechanism of the phenomenon is discussed. Considering the fact that the change in the spectral characteristics occurs throughout the full visible range, this effect may be used for creating the spectrally selective dynamic polarization holographic gratings, displays based on new physical principles, and also for creating modulators and dynamic polarization spectral filters controlled by light.

At the time of research study of the azochromophore-containing polymer materials properties in some high-efficient media, we have observed the anomalous dispersion of photoanisotropy, depending on the energy exposure of linearly polarized actinic radiation. Later, the phenomenon has been called light induced vector polyphotochromism. Spectral Selectivity of Azochromophore-containing Polymer Films in Polarized Light is presented.

Phenomenon of vector polyphotochromism was observed in some high-efficient polarization-sensitive materials dependent on the radiant exposure when material was illuminated with linearly polarized actinic light. The phenomenon has purely vector nature, since under probing by unpolarized light, the transmission spectra of the irradiated and unirradiated area of the material are practically identical. However, an essential change in the transmission spectrum of the material was observed by placing the irradiated area between crossed polarizers when the orientation of the axis of induced anisotropy was of 45 degrees relative to the axes of the polarizers. The dispersion of photoanisotropy was studied at different exposure values. Kinetic curves of the photoanisotropy were obtained for wavelength of 532 nm and 635 nm of probing beam for different values of exposure (30, 60 and 250 J/cm2) with linearly polarized actinic light (457 nm). The dispersion curves of the photoanisotropy were obtained for these values of exposure showing an anomalous behavior for exposures above of 30 J/cm2. This phenomenon was observed in specially synthesized organic materials based on azo dyes introduced in a polymer matrix. The difference between optical densities was obtained for polarized light with a wavelength of 532 nm and 635 nm at different exposures, which makes the prospect the dynamic polarization spectral filters controlled by light and the spectrally selective dynamic polarization holographic gratings to be created.

New stable polarization-sensitive materials are developed on the hydrophobic components basis which doesn't require an additional moisture protection. Bisazodye ortho-tolidinebisazophenol chromophoric component was synthesized which is liposoluble analogue of water-soluble azodye Mordant Pure Yellow M. This bisazodye were used to develop the hydrophobic materials films which can be applied as a protective layer themselves. To increase the thermal stability we have synthesized material by introducing bisazodye into the main-chain of macromolecule of thermally stable polymer. The different types of polarization-holographic gratings with high diffraction efficiency of 30-50% were recorded on the obtained materials by laser beams (441 - 488 nm).

n order to obtain a polarization sensitive materials with improved characteristics, there was conducted intensify interaction between the components of recording media through the interaction between the molecular electrostatic forces. For creating materials there were used various organic dyes capable of photochemical geometric isomerization under the influence of actinic polarized light with a wavelength closed to the maximum of the absorption spectrum of each dye. Various polarization sensitive materials have been synthesized based on the polar water-soluble components. Substantial improvement photoanisotropic characteristics of these materials are revealed due to previously added ionizing functional groups in the chromophoric components. It is shown particular exemplary embodiment of synthesis the materials composed of dyes which communicate with certain polymers via dipole-ionic bonds. The research data of medium properties on their base have been brought up for the consideration. In the same way photoanisotropic materials are created on basis of various polar polymer matrixes which separate macromolecules are capable of establishing dipole-dipole bonds with each other. Thanks to this circumstance a supplementary number of polymer fragments which cannot afford direct connection with dye molecules are also able to get drawing into the photoanisotropy inducting processes. It is displayed the influence of such interactions on material kinetics and value of attainable photoanisotropy. A capability of achievement extremely high values of photoanisotropy is produced on the material samples based on the dyes with expanded number of ionized substituent.

Photoanisotropic properties enhancement by means of introducing ionogenic functional groups into the material azodye component molecules is 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.

The results of the investigation of recording of dynamic polarization-holographic diffraction gratings are presented. Dynamic polarization-sensitive materials with conformation-orientation mechanism of anisotropy induction were used as a recording media. Such media were created on the basis of specially synthesized azodyes introduced into polymer matrices with special physico-chemical properties.

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.

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.

The possibility of applying the photoinduced anisotropy in dynamic polarizationsensitive media for the correction and amplifications of the laser radiation with a complex distribution of the polarization state over the wavefront is tested experimentally

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