Transparent Media Research Articles

Filamentation‐Induced Volume Plasma Grating: Dynamics, Possibilities, and Advantages

AbstractStable propagation of laser filamentation arrays paves new ways for cross‐scale manufacturing. Although a single filament or multiple filaments can be used for laser processing in transparent media, sustainable developments of higher throughput and lower energy consumption are always the pursuit. Here, a proof‐of‐concept approach is proposed in which cross‐scale manufacturing of 3D microstructures is realized via an ionization‐induced volume plasma grating. The volume plasma grating is generated by the noncollinear interaction of two batches of arrays of multiple filaments. The volume plasma grating cannot only regulate the distribution of multiple filamentation but also promote the intensity inside the filaments. By this approach, 3D microstructures are written by 1D sample translation. In addition, rapid fabrications of volume gratings and terahertz wire grid polarizers (THz WGPs) are demonstrated by laser modification using volume plasma grating. The characteristics of the fabricated THz WGPs are comparable to those of commercial ones. The limitations and future implementations of this approach are discussed.

Comparison of temporal cavity indicators when firing “FORT 12R” and “AE 790G1” into a non-biological body simulator

Gunshot injuries are extremely dangerous due to the extremely unpredictable compliance of ammunition after contact with the body. One of the key elements that takes place in this case is the formation due to high kinetic energy of a temporary cavity, which, despite its existence for a fraction of a second, causes severe damage to the tissues of the human body. The study of this phenomenon is one of the central elements of ballistics and requires an experiment on optically transparent media. The purpose of the study is to compare the parameters of the temporal cavity when fired from the “FORT 12R” and “AE 790G1” pistols into a non-biological simulator of the human body. To achieve the goal, 120 gelatin blocks were produced according to the generally accepted method, which were to be shot at close range, 25 and 50 cm. The blocks were left bare before shooting, or covered with cotton fabric, denim fabric or leatherette. After firing, transverse sections of the blocks were made in order to further measure the parameters of the temporary cavity formed as a result of the firing, according to generally accepted methods. The results of the analysis of the received data regarding the indicators characterizing the dimensions of the temporary cavity at different depths of the wound channel revealed a number of significant differences (p<0.05-0.01) between the studied pistols (in almost all cases, “AE 790G1” had larger values), groups of blocks covered with different types of fabrics, bare blocks (in almost all cases, the clothing had protective properties and reduced the size of the temporary cavity) and allowed to establish that during shots from the “FORT 12R” there was a sharp increase in the size of the temporary cavity with its sharp decrease at the end of the wound channel, while with shots from the “AE 790G1” the temporary cavity gradually increases, reaching a maximum at half the depth and then just as gradually decreases. Thus, when comparing the “FORT 12R” and “AE 790G1” pistols, differences in the features of the formation of the temporary cavity were revealed, which in turn is of interest not only for forensics, ballistics and forensic medicine, but also for clinical medicine.

4D Optical Information Storage from LiGa5O8:Cr3+ Nanocrystal in Glass

AbstractWith the fast‐growing amount of data, the state‐of‐the‐art optical data storage has become a front‐runner in the competing data storage technologies. However, two‐dimensional (2D) spatial resolution in the conventional optical data storage media has almost reached the limit. Herein, LiGa5O8:Cr3+ nanoparticles (NCs) precipitated in situ from a transparent medium are prepared. The transparent LiGa5O8:Cr3+ glass ceramics show excellent deep‐trap carriers storage ability under blue light irradiation and can realize the bit‐by‐bit optical data in 3D space for write‐in and read‐out in a photon trapping/detrapping mode. Moreover, this optical storage mechanism is also extended to 4D by realizing temperature optical encryption. Notably, the written information can still be clearly displayed even after being recorded for 200 days. This work enables 4D high‐precision storage of information and provides new insights into the design and fabrication of next‐generation storage materials.

Effectiveness of Snedds (Self-Nanoemulsifying Drug Delivery System) Etil Acetate Fraction of Kadara Fruit (Caesalpinia bonduc) Seed Extract on Bacteria Diabetic Gangreen

High glucose level conditions cause many fatal complications, such as the increased risk of developing gangrene. The incidences of amputation worldwide have happened of 25% and 14.3% mortality after amputation. Patients with diabetic gangrene are often treated with a broad-spectrum antibiotic. However, nowadays antibiotic-resistant bacteria are emerging problems to cure the infection in diabetic gangrene. Scientists are looking for natural compounds to develop new medication as an alternative antibacterial. Kadara (Caesalpinia bonduc) is a plant from Dompu, West Nusa Tenggara. Flavonoids, the primary constituent of Caesalpinia bonduc seeds, are responsible for broad-spectrum antibacterial action. Flavonoids are poorly soluble in water, so as the solution for increasing the stability of flavonoids, it needs development of dosage form in the self-nanoemulsion drug delivery system (SNEDDS). This study aims to determine the effectiveness of the Snedds ethyl acetate fraction of the extract of the seeds of the fruit (Caesalpinia bonduc) against diabetic gangrene bacteria. This research begins with maceration to obtain a thick extract followed by fractionation, then make the SNEDDS formula using the trial-error method. Characterization is carried out, and the antibacterial activity test is carried out. The results showed that the SNEDDS formula that met the criteria was obtained from a comparison of tween 80 and PEG 400 (7:2) with an emulsification time of 29.67±0.58 seconds, a transparent emulsion formation medium, and a particle size of 16.8nm. The results of the bacterial inhibition test showed that the SNEEDS formula was not significantly different from the tetracycline positive control (*p>0.05), with the inhibitory diameter values of 15.67±2.31mm and 15.67±1.15mm.

Cold Sintering of Highly Transparent Calcium Fluoride Nanoceramic as a Universal Platform for High‐Power Lighting

AbstractA thermally robust all‐inorganic color converter is imperative to high‐power light‐emitting diode (LED) lighting. However, it remains challenging to find a universal inorganic matrix for encapsulating multicolor phosphors due to the hurdle of achieving a highly transparent medium at a moderate temperature. Here, the densification of calcium fluoride (CaF2) nanoceramic with visible transmittance up to 75% at merely 350 °C, benefiting from an acid‐mediated cold sintering process of oxygen‐segregated CaF2 nanoparticles is reported. Using the optically isotropic CaF2 as a transparent platform, a Y3Al5O12:Ce3+ (YAG: Ce) phosphor‐based phosphor‐in‐ceramics (PiC) converter with luminous efficacy as high as 190 lm W−1 is fabricated. The ultralow temperature enables the PiC converter to be further combined with red‐emitting CaAlSiN3:Eu2+ (CASN:Eu), delivering a color‐rendering index of 92. The cold‐sintered CaF2 nanoceramic demonstrates great potential as a general solution for next‐generation high‐power LED lighting.

Generation and Controllability of High-Dimensional Rogue Waves in an Electromagnetically Induced Transparent Medium

We propose a scheme to generate and control high-dimensional rogue waves in a coherent three-level Λ-type atomic system via electromagnetically induced transparency (EIT). Under EIT conditions, the probe field envelopes obey the non-integrable nonlinear Schrödinger equations (NLSE) with or without the external potential, which result from the stark (Zeeman) effect contributed by an electric (magnetic) field. By adjusting the amplitude and width of the initial pulse, we can generate the high-dimensional rogue waves and obtain the phase-transition curves of high-dimensional rogue waves. In the system, the far-detuned electric field, the random weak magnetic field, and the Gauss weak magnetic field are not conducive to the excitation of high-dimensional rogue waves. The results not only provide a theoretical basis for the experimental realization or prevention of the high-dimensional rogue waves, but also prove the possibility of generating and controlling the rogue waves in other high-dimensional non-integrable systems.

Stratification of Heterogeneity in the Lithosphere of Mars From Envelope Modeling of Event S1222a and Near Impacts: Interpretation and Implications for Very‐High‐Frequency Events

AbstractWe have modeled the high‐frequency seismogram envelopes of the large event S1222a and four recently identified near impacts recorded by the InSight mission by introducing a stratification of velocity and attenuation into a multiple‐scattering approach. We show that a simple conceptual model composed of a strongly diffusive, weakly attenuating layer overlying a transparent medium captures the essential features of the observed envelopes. The attenuation profiles reveal that the minimal extension of heterogeneities at depth is of the order of 20 km in the vicinity of InSight and 60 km on the path to S1222a. We interpret this result as an indication that the Martian crust as a whole is at the origin of the strong scattering. Our heterogeneity model suggests that the sources of a number of distant Very‐high‐Frequency seismic events are shallow and located to the south or in close vicinity of the Martian dichotomy.

Soliton trains induced by femtosecond laser filamentations in transparent materials with saturable nonlinearity

Femtosecond laser inscriptions in optical media current offer the most reliable optical technology for processing of transparent materials, among which is the laser micromachining technology. In this process, the nonlinearity of the transparent medium can be either intrinsic or induced by multiphoton ionization processes. In this work, a generic model is proposed to describe the dynamics of femtosecond laser inscription in transparent materials characterized by a saturable nonlinearity. The model takes into account multiphoton ionization processes that can induce an electron plasma of inhomogeneous density and electron diffusions. The mathematical model is represented by a one-dimensional complex Ginzburg–Landau equation with a generalized saturable nonlinearity term in addition to the residual nonlinearity related to multiphoton ionization processes, coupled to a rate equation for time evolution of the electron plasma density. Dynamical properties of the model are investigated focusing on the nonlinear regime, where the model equations are transformed into a set of coupled first-order nonlinear ordinary differential equations, which are solved numerically with the help of a sixth-order Runge–Kutta algorithm with a fixed time step. Simulations reveal that upon propagation, spatiotemporal profiles of the optical field and of the plasma density are periodic pulse trains, the repetition rates and amplitudes of which are increased with an increase of both the multiphoton ionization order and the saturable nonlinearity. When electron diffusions are taken into account, the system dynamics remains qualitatively unchanged; however, the electron plasma density gets strongly depleted, leaving almost unchanged the amplitude of pulses composing the femtosecond laser soliton crystals.

MATHEMATICAL MODEL OF DETECTION OF SMALL UNMANNED AERIAL VEHICLES USING ACTIVE OPTICAL SYSTEMS

The work is devoted to the solution of an actual scientific task in the field of civil protection, namely, the development of a new model for the prevention of emergency situations of a terrorist nature at the objects of the critical infrastructure of Ukraine, which are protected, by means of timely detection and identification of small unmanned aerial vehicles by active optoelectronic means. Based on the analysis, it was established that one of the trends in the development of terrorist scenarios at protected critical infrastructure facilities is the use of various small manned and unmanned aerial vehicles to carry out terrorist acts. This work is a continuation of the cycle of previous works on the development of a structural and logical model for managing an emergency situation of a terrorist nature at an object of critical infrastructure of Ukraine, which is protected, caused by the appearance of small-sized aerial targets, intended for the development and constant implementation of procedures of an organizational and technical nature to ensure the safety of the object to the guarded object, when small air targets appear. A mathematical model for the detection of signals reflected from small aerial targets using active optical systems using the phenomena of light absorption and scattering in optically transparent media has been developed, which represents a system of four analytical dependencies. Thus, the mathematical model of detecting signals reflected from small unmanned aerial vehicles using active optical systems using the phenomena of light absorption and scattering in optically transparent media is a system of four analytical dependencies. The first of them allows you to calculate the probability of detecting signals reflected from small air targets. The second determines the expected detection range. The third describes the geometric detection range. The fourth is the energy detection range of signals reflected from small unmanned aerial vehicles by optical systems. Further research will be directed to conducting field experiments, performed using a specially designed laboratory setup, and theoretical calculations of the value of expected target detection activities as part of numerous experiments that should prove the reliability of the results obtained in the work. Keywords: emergency situation, small unmanned aerial vehicle, violator, model, protected object.

Influence of nanoparticle dispersion in a transparent liquid on the spatial characteristics of a four-wave radiation converter

Abstract – The spatial characteristics of a four-wave radiation converter in a transparent heterogeneous polydisperse medium are studied in this paper considering the nanoparticle flow caused by the gravity action with a normal size distribution of particle. Three ranges of average nanoparticle radii (small, intermediate and large), for which different types of spatial spectra of the object waves are characteristic, are distinguished. Shown that in the range of small average nanoparticle radii an increase in the standard deviation leads to an increase in the half-width of the spatial frequency band cut out by a four-wave radiation converter from the spatial spectrum of the object wave. In the range of intermediate average nanoparticle radii an increase in the standard deviation can lead to both an increase and a decrease in the width of the «ring» cut out by a four-wave radiation converter. At large average nanoparticle radii a change in the standard deviation doesn’t affect the spatial selectivity of the four-wave radiation converter.

Damage Threshold in Ablation Regime Induced by Femtosecond Laser Irradiation on Transparent Media

The current work is a case study of ongoing in-depth extensive fundamental research on the plasma formation and relaxation dynamics in transparent media induced by mid- and short-wavelength infrared laser pulses. The experimental investigation is performed on a 35 fs-laser system setup. The working parameters such as laser energy and the number of pulses are varied. The experimental measurements are applied on borosilicate glass samples doped with gold nanoparticles. The effects of the applied laser pulses and their consequence on laser-induced ablation damage thresholds are investigated and discussed. The results from this case study provide valuable information and a deeper understanding plasma formation and dynamics induced by femtosecond infrared laser pulses in solid transparent glass media.

Volume plasma grating by noncollinear interaction of femtosecond filament arrays.

Stable propagation of multifilament arrays in transparent bulk media with adjustable separation distances between adjacent child filaments has always been desired for advanced manufacturing. Here, we report on the generation of an ionization-induced volume plasma grating (VPG) by the interaction of two batches of noncollinearly propagating arrays of multiple filaments (AMF). The VPG can externally arrange the propagation of the pulses along regular plasma waveguides via spatial reconstruction of electrical fields, which is compared with the self-formation of randomly distributed multiple filamentation originated from noises. The separation distances of filaments in VPG are controllable by readily changing the crossing angle of the excitation beams. In addition, an innovative method to efficiently fabricate multidimensional grating structures in transparent bulk media through laser modification using VPG was demonstrated.

Pixelating Structural Color with Cholesteric Spherical Reflectors

While structural color is a powerful means of obtaining saturated and durable pigments that minimize absorption, scattering, and negative environmental impact, appearing naturally in animals and plants as well as in carefully designed artificial composites, it is fundamentally limited to spectral colors, leaving white and other mixed colors elusive. It also normally suffers from a strong viewing angle dependence, making color definition difficult. Herein, it is demonstrated that these challenges can be overcome by using cholesteric spherical reflectors (CSRs), spheres of polymerized cholesteric liquid crystal with radial alignment of the self‐assembled helical structure. Exhibiting omnidirectional selective retroreflectivity of well‐defined color, CSRs are discrete “packages” of structural color. This allows them to be used as pixels for generating nonspectral colors, following the principle of digital displays. A method of creating densely packed monolayers of CSRs with red (R), green (G), and blue (B) retroreflection is developed. Mixing them in equal proportions gives a white surface. By embedding the CSRs in an index matching transparent medium, nonselective specular reflections and scattering are avoided. The approach can be used to create arbitrary colors, including nonspectral ones, without any absorption or nonselective scattering, opening doors to decorating surfaces as desired while minimizing light loss.

Energy efficiency analysis of the radiative transfer of a real medium in thermoforming

Thermoforming involves warming thermoplastics using infrared sources to a desired state in an open oven at atmospheric pressure. The prediction of the distribution of the flux intercepted by the thermoplastic is generally modeled by assuming the surrounding medium transparent. It is within this framework that the present work is placed while aiming at the influence of the temperature and the humidity of the ambient air (gas) on the intercepted energy. To do this, the wide-band model is used to characterize the absorptivity of air vs. the temperature and absolute humidity at atmospheric pressure. The energy efficiency of the radiation emitted by a halogen source and intercepted by a flat surface has been characterized using the temperature of the source and the surrounding environment, humidity, and distance. The temperature of the considered source range 600 K–1500 K, while that of the humid air is in the range 400 K–1000 K for an absolute humidity range 10–80%. The absorptivity of the real gas is modeled by that of a gray gas and the surface-to-surface and volume-to-surface exchange areas are assessed via the Monte Carlo method. From this study, it appears that the error induced by the transparent medium assumption depends on the distance (between lamp and receiver), the lamp temperature, the gas temperature, and its humidity.

Electric field activated ON/OFF surface charge polarization of transparent filter media for high-efficiency PM2.5 filtration

It is a cruel reality that the air we breathe has become an invisible but leading danger in terms of public health and the environment. Exposure to fine particulate matter (PM), and indoor volatile organic compounds (VOCs) is particularly harmful to urban residents among the different airborne pollutants. So far, different types of polymers has been widely used to fabricate filter media for clean air. Most of the developed filter are non-transparent not suitable for window. Moreover, the PMs concentration depends on different factors and fluctuates day-to-week and seasonally. Most present development air filter are non-transparent not suitable for window and single functional by their construction, high fiber diameter and large thickness. Therefore, to meet demands, we introduced a transparent advanced air filters with multi-functionality, such as in situ switch based tuning filtration efficiency, VOC adsorption capability and antibacterial properties. We have rationally designed an electric field activated ON/OFF surface charge polarization air filter composed of nanofiber/nets nanoarchitectured networks with 80% optical transparency. The electric field activated nanofiber/nets filter enhanced PM2.5 filtering efficiency from 61% to more than 95% at a low poling voltage of 0.2 kV. More importantly, here the low voltage is adequate to cause a high electric field (MV m−1) and surface charges can form on the fiber surface. In addition, due to the presence of chitosan in nanofiber/nanonet structure the filter can effectively adsorb gases such as ammonia, triethylamine, and formaldehyde and possessed anti-bacterial behaviour for P. aeruginosa and S.aureus. The approach introduced in this work has the potential to filter PMs under extremely hazardous air conditions and can reduce power consumption by turning off the power during low hazardous conditions.

Imaging Analysis of Scratch Reduction in Poly (Methyl Methacrylate) (PMMA) Plastic with NOVUS Polishing Products

ABSTRACT Remediation of disfiguring scratches and abrasions on aging plastics challenges even the most experienced conservator. This study assesses the effect of three NOVUS polishing products on remediation of poly (methyl methacrylate) (PMMA). Samples were prepared to mimic the depth and type of scratches observed during conservation treatment performed on vacuum-formed reliefs from the 1960s. The study compares samples of new/unaged PMMA to naturally aged PMMA samples. Two different methods were successfully used to assess the polishing efficacy, which is notoriously challenging to document in transparent and reflective media: (1) image segmentation analysis of photographs to yield scratched area fractions, using three approaches (Li-thresholding, random forest, and convolution neural network); and (2) optical profilometry measurements, which provide surface root-mean-square roughness (RRMS) values. Both methods support the qualitative observations that polishing with the abrasive NOVUS products significantly reduced the surface damage; scratch area fractions decreased from 50–60% to 1–5% across the aged PMMA types after treatment, corresponding to an ∼85% decrease in surface roughness. Critically, the two methods are complementary: the image segmentation results demonstrated a greater visible difference between two degrees of polishing treatments on the new material, while profilometry results were able to parse differences in the degree of scratch reduction between the aged and new materials.

Virtual double-slit differential dark-field chromatic line confocal imaging technology.

Chromatic line confocal imaging (LCI) can be used in high-speed 3D imaging of surface morphology, roughness, and multi-layered transparent media in industrial production, quality inspection, and other fields. However, even if they are compensated for or corrected accordingly, the resolution of the built measurement system differs from the theoretical design. In particular, to guarantee high-speed measurement characteristics of the LCI system, a mass center algorithm with poor accuracy is usually chosen for peak extraction, and with the improvement of the manufacturing level, the axial resolution of the measurement system also puts forward higher requirements. Therefore, in this Letter, we propose a virtual double-slit differential dark-field chromatic LCI (VDSDD-LCI) technology. Our approach can reconstruct the optical 3D profile with higher axial resolution and signal-to-noise ratio (SNR) by reducing the full width at half maximums (FWHMs) of the axial response curve without changing the components of the completed LCI system. The experiments on a coin and scrive board surface demonstrate the validity of the proposed method.

A Dynamics of Surface Temperature Forced by Solar Radiation

AbstractDue to lack of a unified description of the Earth surface temperature, a generic dynamic equation is postulated as an inference from the special case of snow. Solar radiation is explicitly included in the formulation for transparent media such as snow, ice and water while implicitly through (conductive) surface heat flux for non‐transparent media such as soil. The physical parameters of the equation are medium thermal inertia, thermal and radiative diffusivity. The equation for transparent media reduces to the familiar force‐restore model of soil surface temperature when the penetration depth of solar radiation tends to zero. Proof‐of‐concept validation for snow surface temperature as a paradigm of transparent media at three sites in the Arctic and Antarctica confirms the postulated equation as a generic description of the dynamics of surface temperature.

Nanosecond laser-induced multi-focusing damage in the bulk of fused silica

A time-resolved imaging system was utilized in this work to study the focusing behavior during laser-induced filamentary damage in the bulk of fused silica. The results show that focusing behavior has a significant dependence on laser energy. With the increased laser energy, single focusing is changed into multi-focusing. The probability of multi-focusing appearances also increases. During this process, the plasma distribution interval increases, which expands the area affected by the damage. The difference in the stress wave velocity indicates that the multi-focusing formation has temporal and spatial order. Finally, the multi-focusing damage’s physical mechanism and formation process are discussed. The results provide a reference for the mechanism of nanosecond laser-induced multi-focusing damage to transparent media.

Single Image Reflection Removal Based on Residual Attention Mechanism

Affected by shooting angle and light intensity, shooting through transparent media may cause light reflections in an image and influence picture quality, which has a negative effect on the research of computer vision tasks. In this paper, we propose a Residual Attention Based Reflection Removal Network (RABRRN) to tackle the issue of single image reflection removal. We hold that reflection removal is essentially an image separation problem sensitive to both spatial and channel features. Therefore, we integrate spatial attention and channel attention into the model to enhance spatial and channel feature representation. For a more feasible solution to solve the problem of gradient disappearance in the iterative training of deep neural networks, the attention module is combined with a residual network to design a residual attention module so that the performance of reflection removal can be ameliorated. In addition, we establish a reflection image dataset named the SCAU Reflection Image Dataset (SCAU-RID), providing sufficient real training data. The experimental results show that the proposed method achieves a PSNR of 23.787 dB and an SSIM value of 0.885 from four benchmark datasets. Compared with the other most advanced methods, our method has only 18.524M parameters, but it obtains the best results from test datasets.