Search Results (18)

Polymer systems induced by the reaction between monomers and photo-initiators play a crucial role in the formation of volume-phase gratings. In this paper, we fabricated a dual-photo-initiator photopolymer by doping EY (Eosin Yellow) molecules into a TI (Titanocene, Irgacure 784@BASF) dispersed PMMA (poly-[methyl methacrylate]) substrate system, with the aim of promoting the diffusion and polymerization processes in volume holographic storage. The two-wave interference system is adopted to record a permanent grating structure in our materials. The temporal diffraction variations of photopolymerization (during the interference exposure) and dark diffusion (after the interference exposure) processes have been investigated and analyzed. Aiming to analyze the influence of EY doping ratios on holographic performances, some key parameters were examined in the experiment. We first measured the temporal evolution of diffraction efficiency, then an exponential fitting was adopted to obtain the response time. Finally, the angular selectivity was evaluated by the Bragg condition after holographic recording. Also, the temporal evolution of each component is described by the nonlocal polymerization-driven diffusion model with a dual-photo-initiator composition, theoretically. Furthermore, we experimentally achieved the holographic grating enhancement in both the dark diffusion and photopolymerization processes by doping appropriate EY concentrations, respectively. This work provides a foundation for the acceptability of TI&EY/PMMA polymers in further holographic storage research. Full article

The behavioral responses of autochthonous organisms have recently been used for a system to monitor the state of fresh and sea waters for bioindication. The advantage of using the behavioral responses of mesozooplankton is determined by the higher sensitivity of such responses compared with changes in the composition of biota or the death of organisms. Earlier, we developed and tested in laboratory conditions and in freshwater reservoirs a submersible digital holographic camera as part of a hydrobiological probe, which allows one to determine the dimensions, shape and recognition of plankters in situ, as well as define the concentration of plankters in the working volume and perform photostimulation with attractive radiation with different levels of illuminance. This paper presents the data obtained during the expedition to the Barents Sea. The variability with regard to the immersion depth of the phototropic response and the interspecific and intraspecific diversity was determined. It was shown that within the framework of natural variability in natural factors (temperature, salinity, hydrostatic pressure, oxygen content, illumination) there are no reliable changes in the indicator response, unlike changes in the concentration of plankton associated with tidal currents. The anthropogenic distortion of water quality was modeled by introducing a saturated salt solution dropwise. There were no significant changes in the intraspecific and interspecific diversity index during the external impact, and the rhythms of tidal changes in the concentration of plankters were suppressed. The fact of increased phototropic sensitivity in crustaceans with a size of less than 120 μm was found. It was established that the most essential marker of the alternating factor was the suppression of the phototropic response. The identified patterns of behavioral responses of autochthonous zooplankton make it possible to create a network of continuous control over the environmental health of water bodies subject to increased anthropogenic impact (oil production zones beyond the Arctic Circle, estuaries and deltas of rivers carrying industrial waste). Full article

Earlier, we showed that the registration of the behavioral responses of autochthonous mesozooplankton communities in situ is a more dynamic methodological approach in the biological assessment of the environmental well-being of aquatic ecosystems, as well as an alternative method to generally accepted tests on mortality and immobilization. The change in behavioral responses, including phototropic responses, may occur at lower concentrations of pollutants, leading to the inhibition of the risk-avoidance response of predatory fish attack and, ultimately, to the change in zooplankton abundance and biodiversity. The biological significance of such changes is quite high since zooplankters form the basis of food chains. This work studies the possibility of biomonitoring the quality of fresh water in Lake Baikal according to the state of the autochthonous mesozooplankton community in summer and winter using a digital holographic camera developed and tested by us in laboratory conditions. This method makes it possible to determine the concentration of plankters in the controlled volume of the DHC and perform photostimulation with different levels of illuminance. The depth profilometry of the phototropic response was compared with the profilometry of plankton concentration, intraspecific diversity of crustaceans according to the Pielou index, and the results of catching using the Juday net in the natural environment of the lake and during the modeling of the anthropogenic impact (introduction of table salt solution into the local area close to the registration probe). The circadian rhythm parameters were determined by the spectral analysis of the long-term registration of the phototropic response dynamics. It was noted that the inhibition of the phototropic response was the most adequate marker of the exogenous impact and the appearance of an alternating factor among the studied indicators of the state of the plankton community, namely, intraspecific diversity, synchronism of circadian rhythms, and response to paired photostimulation. The revealed patterns of behavioral responses of autochthonous zooplankton in natural and artificially modified conditions will allow for the implementation of long-term continuous control over the environmental well-being of water areas, including the collection ponds of treatment facilities, cooling ponds of nuclear power plants, and other water areas in contact with potentially hazardous facilities. The comparison of the identified patterns with the behavioral responses of euryhaline mesozooplankton will expand this method to assess the well-being of salt-water and marine reservoirs under the anthropogenic impact and will make it possible to create a continuous monitoring system. Full article

Our earlier studies showed that paired photostimulation allows the detection of pollutants in an aqueous medium according to the behavioral responses of freshwater Crustacea. The first stimulus initiated and stabilized the behavioral response. The increase in response to the second stimulus made it possible to assess the responsiveness of the zooplankton community. This paper studies the validity of this method for the detection of micro- and nanoplastic contamination of saltwater reservoirs according to the behavioral response of Artemia salina and Moina salina crustaceans. The studies were conducted in laboratory conditions using a submersible holographic camera developed by us, which ensures the in situ detection of the concentration and speed of crustaceans in a volume of up to 1 dm³, as well as makes it possible to change the intensity and duration of the attracting light. It was established that the phototropic response of crustaceans decreases in seawater at the cumulative dose of exposure to microplastics—0.15 mg∙dm⁻³∙h and nanoplastics—0.3 mg∙dm⁻³∙h. The paired photostimulation reveals the altering effect of micro- and nanoplastics in the saltwater medium no later than 3 h after their appearance, which indicates the promising potential of this method for the alarm response in monitoring the environmental well-being of water bodies. Full article

The paper presents the results of in situ studies of marine particles of different nature using a submersible digital holographic camera (DHC) during the Arctic expedition. It also describes the features, performance specifications, and possibilities of the DHC and the DHC technology. The DHC technology can be used for noninvasive automatic evaluation of spatial and temporal characteristics of plankton, including the distribution of plankton concentrations. The comparison of quantitative analysis of zooplankton net samples and classification results using the DHC revealed that the error of the DHC classification of mesoplankton at the level of the main systematic orders was about 30%. The results of determining the data on the medium, such as water turbidity, according to the radiation shielding factor (degree) by the particles of the Suspension taxon using the DHC technology are presented; the prospects for studying the size of gas bubbles and their volume content according to the Bubble taxon data are shown. The use of holographic data for in situ point estimates is considered. Full article

Sc:Ru:Fe:LiNbO₃ crystals were grown from congruent melt by using the Czochralski method. A series of LiNbO₃ crystals (Li/Nb = 48.6/51.4) with 0.1 wt% RuO₂, 0.06 wt% Fe₂O₃ and various concentrations of Sc₂0₃ were prepared. RF1 and RF4 refers to the samples containing 0 mol% Sc₂0₃ and 3 mol% Sc₂0₃, respectively. The photorefractive properties of RF4 were measured by ${\mathrm{Kr}}^{+}$ laser (λ = 476 nm blue light): η_s = 75.7%, τ_w = 11 s, M/# = 19.52, S = 2.85 cmJ⁻¹, Γ = 31.8 cm⁻¹ and ∆n_max = 6.66 × 10⁻⁵. The photorefractive properties of five systems (η_s, M/#, S, Γ and ∆n_max) under 476 nm wavelength from RF1 to RF4 continually increased the response time, while τ_w was continually shortened. Comparing the photorefractive properties of Sc (1 mol%):Ru (0.1 wt%):Fe (0.06 wt%): LiNbO₃ measured by ${\mathrm{Kr}}^{+}$ laser (λ = 476 nm blue light) with Sc (1 mol%):Fe (0.06 wt%):LiNbO₃ measured by He-Ne laser (633 nm red light), η_s increased by a factor of 1.9, V_w (response rate) increased by a factor of 13.9, M/# increased by a factor of 1.8 and S increased by a factor of 32. The ∆n_max improved by a factor of 1.4. A strong blue photorefraction was created by the two-center effect and the remarkable characteristic of being in phase between the two gratings recorded in shallow and deep trap centers. The photorefractive properties (η_S, τ_w, M/#, S, ∆n_max) were increased with an increase in Sc³⁺ ion concentration. Damage-resistant dopants such as Sc³⁺ ions were no longer resistant to damage, but they enhanced the photorefractive properties at the 476 nm wavelength. The experimental results clearly show that Sc-doped two-center Ru:Fe:LiNbO₃ crystal is a promising candidate blue photorefraction material for volume holographic storage. Sc-doped LiNbO₃ crystal can significantly enhance the blue photorefractive properties according to the experimental parameters. Therefore, the Sc:Ru:Fe:LiNbO₃ crystal has better photorefractive properties than the Ru:Fe:LiNbO₃ crystal. Full article

Cloud droplets size distribution (DSD) is one of the significant characteristics for liquid clouds. It plays an important role for the aerosol–droplet–cloud mechanism and variation in cloud microphysics. However, the minuscule sampling space is insufficient for the observation of whole DSD when using high-magnification optical systems. In this paper, we propose an observation method for cloud droplets ranging from 2 to 16 μm, by which the balance relationship between sampling space and optical magnification is realized. The method combines an in-line digital holographic interferometer (DHI) with the optical magnification of 5.89× and spatial stitching technique. The minimum size in DSD is extended to 2 μm, which improves the integrity of size distribution. Simultaneously, the stability of DSD is enhanced by increasing the tenfold sampling volume of cloud droplets. The comparative experiment between the in-line DHI and fog monitor demonstrates that the DSD obtained by this method is reliable, which can be used for the analysis of microphysical parameters. In the Beijing Aerosol and Cloud Interaction Chamber (BACIC), the observation results show that the size of cloud droplets follows the Gamma distribution, which is consistent with the theoretical DSD. The results of cloud microphysical parameters indicate that each pair of parameters has a positive correlation, and then the validity of observation method is confirmed. Additionally, the high-concentration aerosol condition significantly mitigates the effect of random turbulence and enhances the robustness of the microphysical parameter data. Full article

Global warming is a very topical issue, therefore the search for new renewable energy sources is considered of fundamental importance. Among these, solar energy offers great possibilities considering that the amount of sunlight hitting the Earth ‘s surface in an hour and a half is enough to meet the world’s electricity consumption for a complete year. Generally, solar concentrators are used to collect the solar radiation and to concentrate it at a single focal point. These devices consist in a set of mirrors or mechanical structures to reduce the area of a photovoltaic cell, which is typically very expensive. Volume transmission phase holographic optical elements could be opportunely designed and realized to obtain a simple, lightweight, compact and inexpensive planar solar concentrator. With the aim of bringing scientific attention to this still developing topic, in this work we critically report a complete investigation on a new photopolymeric material obtained by sol-gel reactions used as possible recording material for volume holographic solar concentrators; as a proof of concept, both terrestrial and extreme environments, such as space, are considered as potential applications. Full article

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. Full article

We demonstrate a blood analysis routine by observing red blood cells through light and digital holographic microscopy in a microfluidic channel. With this setup a determination of red blood cell (RBC) concentration, the mean corpuscular volume (MCV), and corpuscular hemoglobin concentration mean (CHCM) is feasible. Cell count variations in between measurements differed by 2.47% with a deviation of $-0.26\times {10}^6$ μL to the reference value obtained from the Siemens ADVIA 2120i. Measured MCV values varied by 2.25% and CHCM values by 3.78% compared to the reference ADVIA measurement. Our results suggest that the combination of optical analysis with microfluidics handling provides a promising new approach to red blood cell counts. Full article

A new double-layer sunlight concentration system, where each layer is divided into two regions, is proposed, and the system has four volume holograms. Since the four holograms convert light in different directions, the interlayer crosstalk is reduced, and the system has a high concentration ratio. The simulation results show that the concentration system can achieve a 30° operation angle range. The holograms are fabricated on photopolymer substrates, and the left half of the system is implemented using two holograms. The characteristics of the left half of the system are assessed. The agreement of the simulation and experimental results on diffraction efficiency validates the proposed method. The tested monochromatic concentration ratio can achieve a record of 418.8, and the concentration ratio under sunlight is 5.38. The experiment results of light use efficiency are close to the simulation with non-crosstalk, which indicates that the interlayer crosstalk is small. Full article

Efficient and low-cost solar-energy collection has become the focus of many research works. This paper proposes a recording method and an experimental verification of a wide-band, large-angle, and high concentration-ratio volume-holographic grating for solar concentration. We applied the Kogelnik coupled-wave theory and photopolymer diffusion model to analyse the formation mechanism and influencing factors on the diffraction efficiency of monochromatic volume-holographic gratings. We design and construct a three-color laser-interference system to record three monochromatic volume-holographic gratings. The best recording conditions are determined by experiment and simulation. A trichromatic volume-holographic grating is obtained by gluing the three monochromatic gratings together. The experimental results show that the trichromatic volume-holographic grating with a working angle of 6.7° and a working band of visible light has a light concentration ratio of 149.2 under an illumination of the combined recorded three-color beams, and that under sunlight is 27.2. We find that the proposed trichromatic volume-holographic grating for light concentration offers the advantages of wide band and high light concentration ratio, which provide a reference for solar concentration. Full article

Digital Inline Holography (DIH) is used in many fields of Three-Dimensional (3D) imaging to locate micro or nano-particles in a volume and determine their size, shape or trajectories. A variety of different wavefront reconstruction approaches have been developed for 3D profiling and tracking to study particles’ morphology or visualize flow fields. The novel application of Holographic Particle Counters (HPCs) requires observing particle densities in a given sampling volume which does not strictly necessitate the reconstruction of particles. Such typically spherical objects yield circular intereference patterns—also referred to as fringe patterns—at the hologram plane which can be detected by simpler Two-Dimensional (2D) image processing means. The determination of particle number concentrations (number of particles/unit volume [#/cm ${}^3$ ]) may therefore be based on the counting of fringe patterns at the hologram plane. In this work, we explain the nature of fringe patterns and extract the most relevant features provided at the hologram plane. The features aid the identification and selection of suitable pattern recognition techniques and its parameterization. We then present three different techniques which are customized for the detection and counting of fringe patterns and compare them in terms of detection performance and computational speed. Full article

The use of Holographic Optical Elements (HOEs) in applications, such as in light shaping and redirection, requires certain characteristics such as a high Diffraction Efficiency, low angular selectivity and stability against UV damage. In order to maximize the performance of the HOEs, photosensitive materials are needed that have been optimised for the characteristics that are of particular importance in that application. At the core of the performance of these devices is the refractive index modulation created during holographic recording. Typically, a higher refractive index modulation will enable greater light Diffraction Efficiency and also operation with thinner devices, which in turn decreases the angular selectivity and the stability of the refractive index modulation introduced during recording, which is key to the longevity of the device. Solar concentrators based on volume HOEs can particularly benefit from thinner devices, because, for a solar concentrator to have a high angular working range, thinner photopolymer layers with a smaller angular selectivity are required. This paper presents an optimisation of an acrylamide-based photopolymer formulation for an improved refractive index modulation and recording speed. This was achieved by studying the effect of the concentration of acrylamide and the influence of different initiators in the photopolymer composition on the diffraction efficiency of holographic gratings. Two initiators of different molecular weights were compared: triethanolamine (TEA) and methyldiethanolamine (MDEA). A fivefold increase in the rate of grating formation was achieved through the modification of the acrylamide concentration alone, and it was also found that holograms recorded with MDEA as the initiator performed the best and recorded up to 25% faster than a TEA-based photopolymer. Finally, tests were carried out on the stability of the protected and unprotected photopolymer layers when subjected to UV light. The properties exhibited by this photopolymer composition make it a promising material for the production of optical elements and suitable for use in applications requiring prolonged exposure to UV light when protected by a thin melinex cover. Full article

The possibility of the application of acrylate compositions and Bayfol HX photopolymers in holographic technologies is considered. The holographic characteristics of materials, their advantages, and limitations in relation to the tasks of obtaining holographic elements based on periodic structures are given. The conditions for obtaining controlled two and multichannel diffraction beam splitters are determined with advantages in terms of the simplicity of the fabrication process. The diffraction and selective properties of volume and hybrid periodic structures by radiation incidence in a wide range of angles in three-dimensional space are investigated, and new properties are identified that are of interest for the development of elements of holographic solar concentrators with advantages in the material used and the range of incidence angles. A new application of polymer materials in a new method of holographic 3D printing for polymer objects with arbitrary shape fabrication based on the projection of a holographic image of the object into the volume of photopolymerizable material is proposed, the advantage of which, relative to additive 3D printing technologies, is the elimination of the sequential synthesis of a three-dimensional object. The factors determining the requirements for the material, fabrication conditions, and properties of three-dimensional objects are identified and investigated. Full article