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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.

The photoinduced birefringence of two 4-substituted phthalimide 2-hydroxy Schif bases, containing salicylic (4) and 2-hydroxy-1-naphthyl (5) moieties has been investigated in PMMA matrix. Their optical behaviour as nanocomposite flms was revealed by combined use of DFT quantum chemical calculations (in ground and excited state) and experimental optical spectroscopy (UV–Vis and fuorescence). The results have shown that solid-state reversible switching takes place by enol/keto tautomerization and Z/E isomerization. Birefringence study was performed in the PMMA nanocomposite flms using pump lasers at λrec = 355 nm and λrec = 442 nm. Fast response time and high stability of anisotropy up to 58% for (4) and 95% for (5) after turning of the excitation laser, was observed, which makes these materials appropriate candidates for cutting-edge optical information technology materials. The possibility for multiple cycles of recording, reading and optical erasure of the photoinduced birefringence at λrec = 442 nm in 5 has been demonstrated. The obtained results have shown that the maximum value of the measured birefringence is close to the anisotropic characteristics of the most frequently used azo materials.

Statistical processing of speckle data enables observation of the speed of processes. In intensity-based pointwise dynamic speckle analysis, a map related to speed’s spatial distribution is extracted from a sequence of speckle patterns formed on an object under coherent light. Monitoring of time evolution of a process needs storage, transfer, and processing of a large number of images. We have proposed lossy compression of these images using JPEG and JPEG2000 formats. We have compared the maps computed from noncompressed and decompressed synthetic and experimental images, and we have proven that both compression formats can be applied in the dynamic speckle analysis.

A polarization-sensitive diffractive optical element was recorded in an azopolymer thin film using polarization holography. It acts as a converging lens for left circularly polarized light and as diverging lens for right circularly polarized light.

The dynamic speckle method (DSM) is an effective tool for the estimation of speed of processes. The speed distribution is encoded in a map built by statistical pointwise processing of time-correlated speckle patterns. For industrial inspection, the outdoor noisy measurement is required. The paper analyzes the efficiency of the DSM in the presence of environmental noise as phase fluctuations due to the lack of vibration isolation and shot noise due to ambient light. The usage of normalized estimates for the case of non-uniform laser illumination is studied. The feasibility of the outdoor measurement has been proven by numerical simulations of noisy image capture and real experiments with test objects. Good agreement has been demonstrated in both the simulation and experiment between the ground truth map and the maps extracted from noisy data.

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.

Photoinduced supramolecular chiral structures in azo materials have been extensively studied for the development of all-optical switches and because of their influence on the properties of certain types of polarization holographic gratings. Here, we investigate chiral structures induced by irradiation with elliptically polarized light in thin films of four azopolymers denoted as PAZO, P 1 , P 1 − 2 , which are amorphous, and P 2 , which is liquid crystalline. Their formation is characterized in real time by the kinetics of azimuth rotation. The influence of the irradiation wavelength and intensity is also analyzed. The largest azimuth rotation per unit thickness is achieved in PAZO (33°/µm) and P 1 − 2 (25°/µm). Reversibility of the chiral structures is demonstrated by a tenfold change in the direction of rotation. Our results also indicate that chiral structures formation occurs significantly faster than the induction of linear birefringence.

Azopolymers are highly efficient materials, able to register the polarization state of light. They have broad range of applications from diffractive optical elements with unique polarization properties to biophysics. We present a study of birefringence kinetics, induced with five different pump lasers with wavelengths 355, 442, 491, 514 and 532 nm in thin films of widely used amorphous azopolymer PAZO – poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzene sulfon amido]-1,2-ethanediyl, sodium salt]. During the real-time measurement, the value of the photoinduced birefringence (Δn) is determined at 635 nm, using a DPSS laser. When saturation is reached, the spectrum of the birefringence is measured. Our results indicate that the investigated azopolymer can be used for applications in a wide wavelength range.

Raw data compression is mandatory for monitoring of processes by dynamic speckle analysis when two-dimensional activity maps are built by pointwise statistical processing of correlated speckle patterns formed on the surface of diffusely reflecting objects under laser illumination. Coarse quantization of speckle patterns enables storage and transfer of a huge amount of images, but it may be inefficient at spatially varying speckle statistics, such as for patterns recorded at non-uniform illumination or reflectivity. We prove efficacy of coarse quantization of the raw speckle data with varying statistics for a normalized algorithm by simulation and a polymer drop drying experiment. Both uniform and non-uniform quantization are proposed for treating such data. Decreasing the bit depth from 8 to 3 is possible without worsening the quality of the activity map.

The paper presents a study of the diffraction efficiency of polarization holographic gratings recorded in thin films of the azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]) doped with Cu(II) 3-amino-5,5′-dimethylhydantoin (CLP) and Ni(II) 3-amino-5,5′-dimethylhydantoin (NLP) at three different concentrations, namely 1, 2 and 5 wt.%. The influence of the dopants composition and concentration on the parameters of the polarization holographic gratings recorded in the thin composite films has been discussed. The gratings are recorded with a He-Cd gas laser with wavelength 442 nm. The polarization of the recording beams was left and right circular and the recording angle was 20°. Along with the anisotropic grating in the volume of the media, surface relief is also formed. The diffraction efficiency kinetics is probed at 635 nm and the height of the relief gratings is determined by AFM. Diffraction efficiency (η) higher than 30 % was achieved for the hybrid samples, as well as 585 nm surface relief height.

After its discovery, photoinduced chirality in azopolymer materials has been studied with growing interest because of its potential applications. According to our previous investigations, it is possible to induce chirality in an amorphous azopolymer with a high linear photoanisotropy by illumination with elliptically polarized light. In the present work, we studied the photoinduced chirality in thin nanocomposite films based on the azopolymer poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt], shortly PAZO, doped with TiO2 nanoparticles with a size of about 20 nm. The thickness of the prepared films was approximately 550 nm and the concentration of the nanoparticles varied from 0 to 3 wt. %. A He-Cd laser beam (λ = 442 nm) was used, with the input ellipticity varying from –1 (left circularly polarized) to +1 (right circularly polarized). The ellipticity was set using a quarter-wave and a half-wave plates. We studied the dependences of the output ellipticity and the angle of self-rotation of the polarization azimuth on the input ellipticity. Based on the experimental data obtained, we could analyze the dependence of the self-rotation of the polarization azimuth on the concentration of the nanoparticles. The results show that small concentrations of nanoparticles lead to an enhancement of the self-rotation, hence, the chirality.

We employ two approaches to tune the properties of concurrently inscribed volume polarization and surface relief gratings in nanocomposite thin films containing the azopolymer PAZO (poly[1-4-(3-carboxy-4-hydrophenylazo) benzensulfonamido]-1,2-ethanediyl, sodium salt]) and goethite (α-FeOOH) nanorods. The first one is applied on the stage of sample preparation by varying the concentration of the goethite nanorods from 0% to 15%. Then, different angles between the recording beams are set in the holographic scheme, which allow us to obtain gratings with spatial periods in the range from 0.86 to 2.51 µm. Surface relief modulation close to 300 nm is achieved as well as total diffraction efficiency in the ±1 diffracted orders of more than 50%. The influence of the incorporated goethite nanorods on the properties of both volume birefringence and the surface relief grating are discussed. Xunta de Galicia | Ref. ED431C 2020-06 Bulgarian Ministry of Education and Science | Ref. DCM 353/2020

Industrial inspection of processes by capture of speckle patterns often requires detection of a small activity area buried in a background. This work presents analysis of sensitivity of the dynamic speckle method by processing simulated and experimental correlated in time 8 bit encoded speckle patterns. Simulation of the patterns was done for an exponentially decreasing temporal correlation function of intensity fluctuations by Fresnel propagation of a monochromatic wave reflected from a delta-correlated in time phase screen and captured at different diameters and focal distances of the optical sensor objective lens. For the experiment, we used a 3D printed flat object with hollow sections that was covered with a transparent film and a droplet of a polymer solution and monitored the process of their drying. Both normalized and non-normalized processing algorithms were used.

A conventional Fizeau wedge (FW) is built of two flat reflecting surfaces inclined at a small angle. They form a gap with linearly increasing thickness normally to the wedge ridge. Such FWs with apex angles of 5–100 microradians and 5– 1000 micrometers thickness find application in optical metrology, spectroscopy and laser spectral control. The apex angle, the reflection coefficients and the refractive index in the gap form a unique interference pattern on both FW’s sides. To benefit from a large free spectral range of thin wedges and high spectral resolution of thick wedges, recently we proposed a stack of two FWs with matched parameters. Matching provides the same change of the resonant wavelength at the same lateral displacement of both wedges. The aim of this study is to develop a technique for calculation of the resultant transmission of the stack of two matched wedges at plane wave illumination that is based on determination of the number and optical path differences of the rays leaving the stack at a given point on its rear surface. Only rays with non-negligible contribution as an amplitude are taken into account. Numerical simulation and experimental verification are provided.

Application of the JPEG compression scheme to dynamic speckle patterns captured for visualization of faster or slower changes in 3D objects is analyzed. Compression efficiency is proven by simulation and experiment.

The paper presents preparation of nanocomposite thin films of three newly synthesized perylene bis azo-imides in polyimide matrix by vapour deposition, results of DFT quantum chemical calculations on the optimized molecular geometry of trans (E) and cis (Z) isomers of the studied dyes as well as photoinduced birefringence measurements to explore potential optical application of these novel materials. Vapour deposited single films of the dyes were studied by reflectance UV-VIS and fluorescence spectroscopy in order to investigate the nature of electron transitions and donor-acceptor interactions between phenylazo fragments and perylene core. The nanocomposite films were prepared through vapour deposition of ODA (4,4′-oxydianiline) and PMDA (pyromellitic dianhydride) as the host polymer matrix and of corresponding perylene bis azo-imide dyes as “guest” at two various concentrations 5 % and 10 % w/w. It was found that nanocomposite films have improved photoresponsivness by applying visible light at λ = 532 nm compared to the single deposited films of dyes. This study shows the applicability of the synthesized dyes embedded in the polyimide matrix as visible-light activated molecular switches.

We present a study of the photoinduced birefringence in nanocomposite films of the azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfon amido]-1,2-ethanediyl, sodium salt]) doped with TiO2 nanoparticles (NP) with different concentrations before and after thermal annealing. The NP represent nanopowder with primary particle size 21 nm. The concentration of the NP was varied from 0% (non-doped azopolymer film) to 5 wt%. The thermal process, applied to the nanocomposite films, includes 1 h heating at 200°C. Previous studies of PAZO show that the polymer is stable up to 270°C. We study the dependence of the maximal birefringence induced with He-Cd laser (λ= 442 nm) on the concentration of the TiO2 NP in the azopolymer thin films as well as thermal effect on the absorbance spectra of the thin films. As indicated by our results, the birefringence is higher for the thermally annealed samples. An increase of the photoinduced birefringence is also observed for the nanocomposite layers with 1% NP for the non-annealed films, and with 2% NP for the annealed films.

We present a study of the diffraction efficiencies of polarization holographic gratings recorded in thin films of the azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]). Two series of layers have been prepared using two different solvents – distilled water and methanol. The gratings are inscribed by two plain waves with orthogonal circular polarizations (left and right circular) from a He-Cd gas laser (442 nm) at recording angle 20°, corresponding to grating period 1.3 μm. Higher diffraction efficiency is obtained for the thin film samples spin-coated from the methanol solution for thicknesses below 600 nm. Diffraction efficiency higher than 27% was achieved, as well as surface relief height more than 500 nm.

Pointwise intensity-based statistical processing of dynamic laser speckle patterns formed on the surface of a diffusely reflecting object is perspective for monitoring of ingoing processes of physical or biological activity within the object. The output of the measurement is a two-dimensional map, which shows qualitatively regions of higher or lower activity on the object surface. In the paper, we have proposed transforming the captured 8-bit encoded speckle patterns into binary patterns by applying a pointwise threshold. Motivation behind this study is the need for an algorithm, which is robust to non-uniform illumination and offers lowered computational complexity as time and memory consumption. We showed by simulation and experiment that quality of the map obtained by processing of correlated binary patterns approached that achieved with 8-bit encoded patterns. We analyzed statistical behavior of the estimates built from binary patterns and proved applicability of a non-stochastic threshold as e.g. a constant intensity level at uniform illumination. The proposed algorithm was applied for processing polymer drop drying experimental data.

Undoped and co-doped zinc oxide thin films were deposited on glass substrates using a chemical spray technique. The experimental Lorentz profiles of co-doped ZnO thin films were measured in the spectral region 720–1750 nm. A single oscillator model of the resulted materials is constructed by calculation of: zero-frequency refractive index (no), average interband oscillator wavelength (λo), oscillator strength (So), dispersion energy (Ed), single-effective oscillator energy (Eo), plasma oscillation frequency (ωp) and interband transition strength moments (M−1, M−3).

Pointwise intensity-based algorithms are the most popular algorithms in dynamic laser speckle measurement of physical or biological activity. The output of this measurement is a two-dimensional map which qualitatively separates regions of higher or lower activity. In the paper, we have proposed filtering of activity maps to enhance visualization and to enable quantitative determination of activity time scales. As a first step, we have proved that the severe spatial fluctuations within the map resemble a signal-dependent noise. As a second step, we have illustrated implementation of the proposed idea by applying filters to non-normalized and normalized activity estimates derived from synthetic and experimental data. Statistical behavior of the estimates has been analyzed to choose the filter parameters, and substantial narrowing of the probability density functions of the estimates has been achieved after the filtering. The filtered maps exhibit an improved contrast and allowed for quantitative description of activity. publishedVersion

Here we present two techniques using polarized light for detection of abnormal morphological changes in tissue samples. A Zeta-20 polarized optical microscope has been used to visualize human lung histologic specimens with pathological changes caused by anthracosis, tuberculosis, influenzal pneumonia, pulmonary infarction and malignant tumour formation as well as tissue sample of normal lung. The images have been taken and reconstructed in accordance to the method reported by Jacques and Lee (Lasers in surgery: advanced characterization, therapeutics, and systems VIII: polarized video imaging of skin. In: SPIE. BiOS ’98 international biomedical optics symposium, vol 3245, San Jose, CA, USA, 1998. https://doi.org/10.1117/12.312307). Tissue polarimetry has been also used to study the above-mentioned biological samples. The experimental set-up working in reflectance geometry consisted of a DPSS LASER with wavelength of 635 nm, which passes through linear polarizer, quarter wave-plate and focusing lens before reaching the biological sample at illumination angle of 45°. Basic polarimetric parameters such as azimuth, angle of ellipticity, degree of polarization and illuminating power were measured and used to evaluate the change in the polarisation state of the incident light after interaction with the biological samples.

Characteristics of polarization holographic gratings (PHG) in non-covered azopolymer thin films and azopolymer films covered with glass slide are compared. An improvement of the polarization properties of the PHG in the covered films is established.

Analysis of dynamic speckle patterns enables visualization of faster or slower changes for 3D objects. Compression of data in this type of metrology by coarse quantization at nonuniform illumination is studied by simulation and experiment.

Dynamic speckle analysis is a promising tool for inspection of speed of processes. It relies on highly sensitive of speckle phenomenon to micro-changes in the optical paths. The same phenomenon is a source of severe noise, which contaminates substantially the outcome of analysis when a pointwise processing is applied to correlated in time speckle patterns. We obtained improvement of quality of the two-dimensional activity map produced by the pointwise processing by illumination at two wavelengths in the red and green part of the spectrum and separate processing of the raw data acquired in the red and the green channels of a color camera used to capture the speckle patterns. Summation of the activity maps corresponding to the two channels results in narrower spread of fluctuations of the estimate chosen to describe the activity.

Dynamic speckle analysis is a highly sensitive approach for monitoring speed of processes, which cause change in micro-topography of the surface of 3D objects. The raw data are speckle patterns formed on the surface under laser light illumination. Statistical pointwise processing of correlated in time speckle patterns yields a 2D map of the ongoing activity, that shows regions of faster or slower fluctuations of laser light intensity. The map is a distribution of a given estimate, which is contaminated by signal-dependent noise due to averaging over a finite number of speckle patterns. For this reason, efficiency of processing is frequently addressed topic. This paper studies the impact of the speckle contrast on quality of the activity map characterized by the spread of the probability density function of the activity estimate. It has been shown by simulation and experiment that retrieval of different activity regions is effective at low contrast of the speckle patterns.

Upon polarimetry the polarization state of light can be obtained for different depolarizing or non-depolarizing medias such as biological specimens. Tissue polarimetry can facilitate a differentiation between healthy and (pre)cancerous tissues, without using any contrast agents and ionizing radiation. Early cancer detection is vital to increase the life expectancy of patients. Turbid medias like biological tissues can change the state and/or decrease the initial polarization of light. Circularly polarized light is preferred as found to possess better ability to detect abnormal changes in tissues, compared to linearly polarized light. In this paper we analyse polarimetric parameters, measured with Thorlabs Stokes meter included in tissue polarimetric experimental set- up in reflection geometry and multiple ex vivo colon samples. The polarimetric device operates in the spectral range between 400 nm and 700 nm, where all experiments had been conducted with wavelength of 635 nm. By reaching reference values for the polarimetric parameters we can propose a theoretical Mueller matrix, that can be used to describe the depolarization properties of the colon samples used in the experiments. The proposed Mueller matrix is to be modelled and experimentally validated to find out if it matches the theory and can be further decomposed to three matrices of depolarization, diattenuation and retardance. All of the aforementioned experimental approaches are a step closer to a pre-clinical trial, which is a bridge to the final and the most challenging goal - tissue polarimetric set-up for in vivo diagnostics.

The work presents preparation, structural investigation and optical properties determination of composite films based on the azopolymer (poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt]), shortly PAZO, doped with 1 wt.% particles of the previously synthesized by us new tellurium containing chalcogenide system (GeTe4)100-xCux, where x = 5, 10, 15 and 20 mol.%. X-Ray diffraction (XRD) was applied to analyze the structure of the chalcogenide bulk material. Transmission electron microscopy (TEM) has been used to study the particles and the composite films morphology. The transmittance coefficient (T), the reflectance coefficient (R), the refractive index (n), the extinction coefficient (k), the optical absorption coefficient (α) and the optical band gap (Egopt) of the composite films were determined. Birefringence was induced by a He-Cd laser with a wavelength 442 nm and measured with probe Diode Pumped Solid State (DPSS) laser at 635 nm. The influence of the dopants concentration on the optical performance of the composite films has been discussed.

Recently, a birefringence enhancement effect was observed in azopolymers doped with various nanoparticles. The paper presents comparison between the parameters of polarization holographic gratings recorded in a pure azopolymer PAZO (Poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]) and in a hybrid PAZO-based organic/inorganic material with incorporated ZnO nanoparticles of size less than 50 nm. Laser emitting at 491 nm is used for the holographic recording. Along with the anisotropic grating in the volume of the media, surface relief is also formed. Gratings with different spatial frequencies are obtained by varying the recording angle. The time dependence of the diffraction efficiency is probed at 635 nm and the height of the relief gratings is determined by AFM. Our results indicate that both the diffraction efficiency and the height of the surface relief for the hybrid samples are enhanced with respect to the pure azopolymer films.

An important goal in the development of diffractive optical elements is to achieve high diffraction efficiency. One class of these elements are the surface relief gratings recorded by polarization holography. For recording media, we used azopolymer (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]), shortly denoted as PAZO. The aim of the present work is to simulate a highly efficient surface relief grating formed in the azopolymer PAZO. The model is based on experimental results already obtained by our group. The tasks of the research are related to the analysis of the diffraction efficiency in the spectral range from 300 nm to 800 nm and for: 1) range of grating spatial frequencies from 1200 ln/mm to 1800 ln/mm, 2) surface relief height varying from 100 nm to 400 nm and 3) different shapes of the formed relief.

We present study of the parameters of polarization holographic gratings recorded in thin films of the azopolymer PAZO (Poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]) and in a composite PAZO-based organic/inorganic material with incorporated TiO2 nanoparticles with size 21 nm and different concentrations. The gratings are inscribed by two plane waves with left and right circular polarization from a He-Cd gas laser (442 nm) at recording angle 20°. Along with the anisotropic grating in the volume of the media, surface relief is also formed. Gratings with different spatial frequencies are obtained by varying the recording angle. The diffraction efficiency kinetics is probed at 635 nm and the height of the relief gratings is determined by AFM. Our results indicate that the diffraction efficiency for the hybrid samples is enhanced with respect to the pure azopolymer films. Comparison is also made between polarization response of samples deposited from water and from methanol solution.

Tissue polarimetry provides a non-invasive, fast and relatively cheap differentiation of healthy from tumor tissues. This approach uses the different manner in which healthy tissues depolarize light, compared to the tumor ones. In extremely scattering optical media, such as biological tissues, light undergoes multiples scattering events, leading to changes in the two orthogonal components of the electric field Ex, Ey and a phase shift between them, which partially or fully depolarizes the initial polarization. When the size of the scattering particles is less than the wavelength of light (d < λ), then the linear polarization is preserved better. On the contrary, when the size of the scattering particles is greater than the wavelength of light (d > λ), then the circular polarization is preserved better. Measuring the Stokes parameters of light with linear and circular polarization and wavelength λ = 635 nm, diagnostic conclusions might be obtained for the histological condition of the samples, which are in agreement with the analysis of the pathologists. Moreover, this approach optimizes the differentiation based on polarization properties for the investigated soft tissues samples.

The implementation of tissue polarimetry in medicine arises mainly for the need of non-invasive and highly sensitive discrimination between healthy and tumor tissues. This fast, relatively cheap method may be useful for better histological diagnostics by the physicians. Although, the most challenging goal is to apply tissue polarimetric optical system for in vivo measurements, initially one have to optimize the optical system using ex vivo histological samples, phantoms and etc. This paper is focused on the polarimetric parameters from lower gastrointestinal tract histological samples, by using polarized light with several wavelengths, namely 444 nm, 488 nm, 514 nm, 594 nm and 635 nm, detected and processed by commercially available polarimeter. Our experimental results reveal the best wavelength choice in favor of 635 nm for all colon samples used. Light with circular polarization was used in the experiments, as found to survive more scattering events, compared to linearly polarized light. Furthermore, circularly polarized light carries additional information about the phase difference between the two orthogonal components of the electric field (Ex and Ey) and in the case of reflection, the incident state of polarization undergoes a ip of its helicity. By this way, a better detection of histological changes in tissues, related to abnormal tissue structure can be made. Furthermore, the multiwavelength, polarimetric analysis may provide better insight for future in vivo implementation and the results from the ex vivo biological samples presented in this study, contribute to better discrimination based on optical measurements, applicable for tumor detection.

We present a study of the birefringence photoinduced in thin nanocomposite films of an azopolymer (PAZO) doped with different concentrations of nanoparticles (NPs) of ZnO with spherical shape and size in the range 40 – 100 nm. The nanocomposite thin films were prepared by electrospray deposition of ZnO over a thin azopolymer film with a thickness below 200 nm. The different NPs concentrations were obtained through different electrospray deposition times varied from 0 to 10 minutes. Birefringence was induced by a He-Cd laser at a wavelength of 442 nm and measured by a probe diode pumped solid state (DPSS) laser at 635 nm. The birefringence dependence on the ZnO NP deposition time reached its maximum for a deposition time of 90 s.

Polarization holography offers the possibility to register not only the intensity and phase of light, but also its polarization. When the interfering beams are with orthogonal linear polarizations, in addition to the photoinduced linear birefringence in the media, chiral structures are formed. They strongly influence the properties of the recorded polarization diffraction gratings. In the present work, we study photoinduced chirality in thin films, based on the azopolymer poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt], shortly PAZO. Nanocomposite samples are also studied, prepared from the same azopolymer, doped with TiO2 nanoparticles with size 21 nm. Exciting light from a He-Cd laser ( λ = 442 nm) has been used, with input ellipticity varying from –1 (left circularly polarized light) to +1 (right circularly polarized light). The dependences of the output ellipticity and the angle of self-rotation of the polarization azimuth on the input ellipticity are presented. This allows us to estimate the effective value of the photoinduced circular birefringence and to evaluate the diffraction efficiency of a polarization holographic grating recorded with two plane waves with orthogonal linear polarizations.

Herein, we report the synthesis and E→Z photoswitching behavior of two 4-substituted azomethine phthalimides containing anthracenyl and 4-(dimethylamino)phenyl moieties (EAMP1 and EAMP2). These compounds represent newly synthesized and unstudied photoswitches with dual fluorescence properties as E-isomers and at photostationary state (PSS) depending on the solvent polarity. Steady-state fluorescence measurements were performed in various solvents and the results show strong sensitivity on the environmental polarity. The kinetics of E→Z photoswitching to PSS was studied in AcCN by visible light activation at 410 nm (EAMP1) and long wavelength UV-light activation at 350 nm (EAMP2). The quantitative and qualitative performance of the switching behavior was evaluated by the degree of photoisomerization (R) and the rate constant (k). It was found for EAMP1 R = 6.95 %, k = 8.87 × 10−4 s−1 and EAMP2 R = 88.72 %, k = 4.00 × 10−4 s−1, respectively. The reason for the lower photoconversion of EAMP1 compared to the EAMP2 was analyzed through optimization of the molecular geometry of E- and Z-isomers in the ground state (S0) and first excited state (S1) by DFT/TD-DFT calculations with B3LYP/6-31+G(d,p) level of theory using IEFPCM in AcCN. It was found that E-isomers in the S0 have nonplanar conformation, while the Z-isomer of EAMP1 prefers twisted conformation and the Z-isomer of EAMP2 T-shaped conformation is energetically advantageous compared to the twisted one. The reason is the weak H…..π noncovalent interaction (NCI) between 4-(dimethylamino)phenyl moiety and phthalimide ring. Moreover, the Z-isomer of EAMP2 is unusual stable up to 600 min at room temperature in dark compared to the EAMP1, which undergoes full Z→E relaxation for less than 60 min at the same conditions. The Z→E relaxation of EAMP2 is achieved for 90 min at 60 °C. The fluorescence E→Z switching behavior was studied by emission measurements in AcCN and 1,4-DOX as E-isomers and at PSS in room and liquid nitrogen (77 K) temperatures. In the polar and nonpolar solvents, red-shifted emissions with increased fluorescence quantum (Φfl) yields have been observed at PSS compared to the E-isomers. The molecular rotor behavior was studied in the binary mixture of glycerol:ethanol and the results show a sensitivity of the emission bands depending on the environmental viscosity. Time-resolved fluorescence decay measurements were performed in AcCN and 1,4-DOX as E-isomers and at PSS to estimate the mechanism of fundamental fluorescence bands. We found that dyes at PSS have longer lifetime (τ) compared to the E-isomers, especially in less polar 1,4-DOX.

Azopolymers are one of the most efficient materials able to record the polarization state of light. They have numerous applications, such as data storage and diffractive optical elements with unique polarization properties. An essential parameter for each diffractive element is its diffraction efficiency η. In order to optimize the recording conditions and obtain high-efficient polarization holographic gratings, in the present work we study the dependence of the diffraction efficiency on the recording angle and thickness of a series of azopolymer layers. Three recording angles are used − 10°, 20° and 30° and three series of thin films with thicknesses 470, 850 and 2400 nm from the water-soluble azopolymer PAZO. The gratings are inscribed by two plain waves with left and right circular polarization from a He-Cd gas laser (442 nm). The diffraction efficiency of the gratings is probed with a right hand circularly polarized beam from a probe laser with wavelength 635 nm. The kinetics of diffraction efficiency η(t) in the + 1 diffraction order are presented and compared. Our experimental results indicate that highest diffraction efficiency (more than 40%) is obtained for the sample with thickness 2400 nm and for recording angle 10°. As the holographic recording in azopolymers is usually accompanied by formation of surface relief gratings, the surface topography of the recorded samples is also investigated by atomic force microscopy.

A variety of biomedical and food quality assessment tasks have been solved by statistical processing of speckle patterns formed on the surface of diffusely reflecting objects. The output of pointwise processing of a temporal sequence of correlated speckle images is a two-dimensional spatial contour map which characterizes the time scales of the ongoing physical or biological activity within the studied objects. In this work, we check efficiency of the dynamic speckle analysis for temporal characterization of migration of cosmetic ingredients from the skin surface to the lower skin layers. At illumination with a He–Ne laser, formation of speckle patterns on the skin surface is governed by the diffusely reflected photons which have undergone a lot of scattering events in the bulk of the tissue. This entails low time-correlation of the formed speckle patterns. Activity maps have been built for sections of treated and non-treated skin on the arm of a volunteer. We found out that a bare skin exhibited high activity which decreased for a skin treated by a cream or cosmetic oil. We proved that the observed difference between the activity maps for a bare skin and a treated skin would allow for monitoring of the time scales of penetration of various cosmetic products into the skin to perform their quality assessment.

Azobenzene containing polymers are a class of optical materials extensively investigated in the past decade. Due to their possibility to undergo reversible trans-cis-trans photoisomerization cycles and through their attractive photophysical properties, the azopolymers could be used as storage medium in optical devices, as optical switches and sensors, as responsive surfaces for biomedical applications, in polarization holography, and in photonics. The aim of this paper is to summarize the information available in the scientific literature about the possibility to use these materials not only for optical application but also as sensing platforms for the detection of biological agents listed as category A biological weapons. Furthermore, this review attempts to give the readers insights into the difficulties concerning the detection of biological agents within environmental samples as well as to outline the progress and the weaknesses in the development of sensors based on nanostructured materials to help to combat terrorisms.