Absorption Phenomena Research Articles

Controllable probe absorption spectrum via vortex beams excitation in a cascaded atomic system

Dynamic control of probe absorption spectrum via vortex beams in multilevel systems has attracted much attention because it provides an avenue to observe unique transport properties. In this paper, we employ experimentally accessible parameters to flexibly control the probe absorption spectrum that shows vortex-induced transparency (VIT) and absorption (VIA) phenomena. Specifically, this system can be served as an optical switch while the vortex beams can act as the control knob, which has the ability to switch from a transparency dip to an absorption peak. Differing from a conventional electromagnetically induced transparency technique, our proposed scheme investigates VIT and VIA by tuning the orbital angular momentum of vortex beams in the resonance and non-resonance cases. Moreover, the collective feature caused by constructive or destructive interference is also studied via adjustable frequency detuning. Our results may provide an efficient approach to study similar phenomena in multilevel quantum systems driven by optical vortex beams.

First principle theoretical designing of W-shaped Dithienosilole-based acceptor materials having efficient photovoltaic properties for high-performance organic solar cells

The key strategy to enhance the intra-molecular push-pull effects by broadening the optial absorption of small molecule based organic photovoltaic (SM-OPV) materials is considered an effective approach to enhance the power conversion efficiencies (PCEs) of SM-OPV devices. However, in case of acceptor materials, the highly desirable molecular modelling strategy of halogenation generally effects in downward-shifting of molecular energy levels, resulting decrease in open-circuit voltages (Voc) in the devices. Herein, we investigate a fluorinated, chlorinated and cyanide (CN) based end-capped acceptor materials, which shows a broader optical absorption phenomenon and exhibited a good voltages than it chlorinated counterparts. These new molecularly engineered SM-OPV were characterize theoretically by density functional theory (DFT) and time-dependent (TD-DFT) approaches. The estimation of electron/hole mobility, and Voc was done by calculating the geometric parameters, electronic structures, frontier molecular orbitals (FMOs), charge transfer rates, and exciton binding energies of the designed OPV materials. The outcomes of these investigations revealed that all newly engineered SM-OPV acceptor materials displays an enhanced exciton dissociation and absorption efficiency and underneath LUMO levels which might be responsible to improve the Voc, reorganization energies, and photo-current density parametrs, resulting enhancement in the PCEs of the organic solar cells (OSC) devices.

Development of Single layered, Wide angle, Polarization insensitive Metamaterial Absorber

The simultaneous achievement of multiband absorption, polarisation-insensitive, and angularly stable absorber is a difficult job. Therefore, in this article, an efficient single-layered absorber is designed, critically analysed, fabricated, and experimentally validated. The proposed model incorporates eight sectors loaded a circle inside the square. The four discrete absorption peaks are observed at 4.4 GHz, 6.0 GHz, 14.1 GHz, and 16.0 GHz manifesting absorption intensities of 94%, 84%, 82%, and 92%, respectively. Parametric studies have been also exercised to investigate the influence of discrete geometrical design variables on the proposed absorber. The proposed structure is symmetrical in geometry, consequence in polarisation-independent behaviour. The absorption mechanism is also explained by analysing the surface current, electric field, and magnetic field distributions. Besides, the complex electromagnetic parameters are extracted to realise the absorption phenomenon. Additionally, to validate the simulated results, an optimal sample is fabricated and the measured response is well-matched with simulated ones.

선형 스플라인 보간법을 활용한 교류철도 고장점표정 보정기법에 대한 고찰

In this paper, we compare and analyze the characteristics of the boosting current ratio, which occurs differently depending on the ground configuration of the traction line, to derive the main causes of the fault location error. To this end, the Power system analysis program (PSCAD/EMTDC) is utilized to derive the characteristics of the boosting current ratio due to the other-line absorption phenomenon through modeling and simulation. Furthermore, to derive problems from existing calibration methods, we analyze facial expression errors by classifying single linear interpolation calibrations into multiple cases. We present a correction technique using linear spline interpolation to improve the accuracy of the fault point representation even under the nonlinear boost current ratio characteristic conditions due to integrated ground and other line absorption phenomena.

JUSTIFICATION OF THE POSSIBILITY OF USING THERMOMODIFIED VENEER IN AN ENVIRONMENT WITH HIGH HUMIDITY

Thermally modified wood is widely used in the woodworking industry, as it has increased resistance to environmental factors (humidity, temperature). The effect of high temperature on wood causes a decrease in water adsorption by reducing the available free hydroxyl groups of carbohydrates. The reduction in hygroscopicity contributes to the treated material size stability, as swelling and shrinkage are mainly associated with the phenomena of absorption and water desorption. The study of natural weathering always takes many years. Therefore, to study the resistance of thermodified wood to environmental influences, artificial weathering is used - modeling of external factors (cyclic change of UV light and moisture). The effectiveness of the thermodified veneer use as a material for lining the furniture facades which working in different temperature and humidity conditions was established. The values of moisture and water absorption on the samples of oak veneer, which have previously undergone the heat treatment process, have been determined. It was found that the samples of oak veneer gained the most moisture from the environment in the first two days. The weight of unmodified veneer increased by 0.06 g, similar results showed veneer modified at temperatures of 160 and 190 °C. Thermodified veneer at a temperature of 250 °C for the first two days gained twice less. By the end of the experiment (next 11 days), the samples of ordinary and modified veneer at all temperatures absorbed the same amount of moisture. Untreated veneer and thermodified at temperatures of 160 and 220 °C absorbed 50-66 % of its initial weight, and modified at 250 °C – 20-36 %. Control samples of veneer during the determination of water absorption gained 98 % of the initial weight. Samples modified at 160 °C – 10, 20, 30 min showed the best result – reducing the value to 94 %, 93 % and 91 %. There is a slight improvement in water absorption after exposure to temperature 220 °C for 10, 20, 30 min – 91 %, 91 % and 90 %. Values water absorption at the level of 90 %, 89 % and 86 % were recorded in veneer samples modified at 250 °C.

Polarization independent triple band ultrathin conformal metamaterial absorber for C- and X-frequency bands

A triple-band polarization-independent conformal absorber for C- and X-frequency bands have been presented. The designed absorber comprises a Jerusalem cross resonator at the center, surrounded by a quarter part of a square rings resonator with different sizes at each corner on a metal grounded dielectric substrate. The unit cell size is 0.23λo × 0.23λo and thickness of λo/153 at frequency 6.16 GHz. The absorption peaks were obtained at frequencies 6.16 GHz, 9.22 GHz, and 11.6 GHz with absorptivity 95%, 96%, and 97%, respectively. It exhibited full wave at half maximum (FWHM) bandwidths of 160 MHz bands (6.04 GHz–6.20 GHz, 240 MHz (9.09 GHz–9.33 GHz), and 260 MHz (11.57 GHz−11.83 GHz), respectively. The designed absorber is shown four-fold symmetry, which makes it polarization independent. Normalized impedance and surface current distributions for all three absorption frequencies are analyzed for understanding the absorption phenomenon. The designed absorber has been tested for the curved surfaces with different central angles to show its conformal behavior, and it is perceived that measured results and simulated results have good agreement between them.

Multi-band terahertz resonant absorption based on an all-dielectric grating metasurface for chlorpyrifos sensing.

Perfect metasurface absorbers play a significant role in imaging, detecting, and manipulating terahertz radiation. We utilize all-dielectric gratings to demonstrate tunable multi-band absorption in the terahertz region. Simulation reveals quad-band and tri-band absorption from 0.2 to 2.5 THz for different grating depths. Coupled-mode theory can explain the absorption phenomenon. The absorption amplitude can be precisely controlled by changing the pump beam fluence. Furthermore, the resonant frequency is sensitive to the medium's refractive index, suggesting the absorber may be of great potential in the sensor detection field. The experimental results exhibit a high detectivity of pesticides.

Tuning the nonlinear optical properties by engineering donor-acceptor configurations in nitrochalone derivatives

Development of tunable photonic devices having molecular dimensions is an active research area in nonlinear optics which continues to evolve and impact many technologies. Here, we demonstrate the tailoring of nonlinear optical properties of nitrochalcone derivatives by engineering the donor-acceptor configurations on either end of the molecules, to control the intramolecular charge transfer process. The central π-bridge in chalcones provides delocalized electrons which lead to the nonlinear polarizability observed in these molecules. Optical nonlinearity is studied by means of second harmonic generation (SHG) and open aperture Z-scan measurements. Samples show optical limiting behaviour in the nanosecond excitation regime due to excited state absorption (ESA) and two-photon absorption (2PA) phenomena. Our study highlights the importance of structure-property correlations in molecular designs.

Presence, flow, and narrative absorption: an interdisciplinary theoretical exploration with a new spatiotemporal integrated model based on predictive processing

Presence, flow, narrative absorption, immersion, transportation, and similar subjective phenomena are studied in many different disciplines, mostly in relation to mediated experiences (books, film, VR, games). Moreover, since real, virtual, or fictional agents are often involved, concepts like identification and state empathy are often linked to engaging media use. Based on a scoping review which identified similarities in the wording of various questionnaire items conceived to measure different phenomena, we categorize items into the most relevant psychological aspects, and use this categorization to propose an interdisciplinary systematization. Then, based on a framework of embodied predictive processing, we present a new cognitive model of presence-related phenomena for mediated and non-mediated experiences, integrating spatial and temporal aspects and also considering the role of fiction and media design. Key processes described within the model are: selective attention, enactment of intentions, and interoception. We claim that presence is the state of perceived successful agency of an embodied mind able to correctly enact its predictions. The difference between real-life and simulated experiences (“book problem,” “paradox of fiction”) lays in the different precision weighing of exteroceptive and interoceptive signals.

Effect of transition metal Mn2+ ion doping on the structural, spectral and photoluminescent properties of NaSrVO4 prepared by combustion synthesis

The paper presents a simplistic way to synthesize NaSr(1−x)VO4:xMn2+ nanophosphors with 0.25 ≤ x ≤ 3.0 mol% by using combustion synthesis route in which urea is used as an organic fuel. The structural, spectral and optical properties were examined using XRD, UV–Vis spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Photoluminescence (PL) spectroscopy. Doping the host with Mn2+ ions created the mid gap absorption phenomenon. Initially, a red shift is observed in the band gap for low amount of the transition metal ion Mn2+ in NaSrVO4 host which is followed by an augment in the band gap values for higher concentrations. Photoluminescence properties shows that under excitation at 380 nm, sample possess two prominent emissions peaking at 434 nm and 523 nm. This phosphor material may possibly be considered of as a new material to be excited by UVA emitting InGaN LEDs.

On the Transmittance of Metallic Superlattices in the Optical Regime and the True Refraction Angle

Transmission of electromagnetic fields through (dielectric/metallic)n superlattices, for frequencies below the plasma frequency ωp, is a subtle and important topic that is reviewed and further developed here. Recently, an approach for metallic superlattices based on the theory of finite periodic systems was published. Unlike most, if not all, of the published approaches that are valid in the n→∞ limit, the finite periodic systems approach is valid for any value of n, allows one to determine analytical expressions for scattering amplitudes and dispersion relations. It was shown that, for frequencies below ωp, large metallic-layer thickness, and electromagnetic fields moving along the so-called “true” angle, anomalous results with an apparent parity effect appear. We show here that these results are related to the lack of unitarity and the underlying phenomena of absorption and loss of energy. To solve this problem we present two compatible approaches, both based on the theory of finite periodic systems, which is not only more accurate, but has also the ability to reveal and predict the intra-subband resonances. In the first approach we show that by keeping complex angles, above and below ωp, the principle of flux conservation is fully satisfied. The results above ωp remain the same as in Pereyra (2020). This approach, free of assumptions, where all the information of the scattering process is preserved, gives us insight to improve the formalism where the assumption of electromagnetic fields moving along the real angles is made. In fact, we show that by taking into account the induced currents and the requirement of flux conservation, we end up with an improved approach, with new Fresnel and transmission coefficients, fully compatible with those of the complex-angle approach. The improved approach also allows one to evaluate the magnitude of the induced currents and the absorbed energy, as functions of the frequency and the superlattice parameters. We show that the resonant frequencies of intra-subband plasmons, which may be of interest for applications, in particular for biosensors, can be accurately determined. We also apply the approach for the transmission of electromagnetic wave packets, defined in the optical domain, and show that the predicted space-time positions agree extremely well with the actual positions of the wave packet centroids.

Infrared all-dielectric Kerker metasurfaces

The unidirectional scattering of electromagnetic waves in the backward and forward direction, termed Kerkers' first and second conditions, respectively, is a prominent feature of sub-wavelength particles, which also has been found recently in all-dielectric metasurfaces. Here we formulate the exact polarizability requirements necessary to achieve both Kerker conditions simultaneously with dipole terms only and demonstrate its equivalence to so-called "invisible metasurfaces". We further describe the perfect absorption mechanism in all-dielectric metasurfaces through development of an extended Kerker formalism. The phenomena of both invisibility and perfect absorption is shown in a 2D hexagonal array of cylindrical resonators, where only the resonator height is modified to switch between the two states. The developed framework provides critical insight into the range of scattering response possible with all-dielectric metasurfaces, providing a methodology for studying exotic electromagnetic phenomena.

Quantum chemical design of near‐infrared sensitive fused ring electron acceptors containing selenophene as π‐bridge for high‐performance organic solar cells

AbstractEnd‐capped acceptors modification of fused ring electron acceptors (FREAs) is an attractive strategy to boost the optoelectronic and photovoltaic properties of the materials. FREAs are also proven beneficial due to their tremendous applications in organic solar cells (OSCs). Among fused‐ring electronic species, small fullerene‐free FREAs have already been drawn more attention due to their near‐infrared sensitivity and constantly increasing efficiencies. Therefore, we have designed six new FREAs (K1–K6) having selenophene as π‐bridge in between the central alkylated indaceno[1,2‐b:5,6b]dithiophene (IDT) unit after the incorporations of various end‐capped acceptors on to the recently synthesized IDT2SeC2C4‐4F molecule. Structural–property relationship and photophysical and photovoltaic properties of newly designed molecules are studied with the help of density functional theory (DFT) and time‐dependent DFT (TD‐DFT). Certain critical specifications like frontier molecular orbitals (FMOs) alignment, density of states (DOS), absorption maxima, excitation energy, binding energy (BE) along with transition density matrix (TDM), and the specifically estimated reorganizational energy values of electron and hole and the open circuit voltages of newly designed molecules are computed and compared with reference molecule. Generally, a red‐shifting absorption behavior of FREAs is considered the most important reason for their high efficiencies in OSCs. Our novel designed molecules exhibit red shift in absorption spectrum. Similarly, low excitation and binding energies of designed molecules offer improved power conversion efficiencies (PCEs) with highest possible charge photocurrent density (Jsc) in OSCs devices. Furthermore, study of PTB7‐Th/K1 complex is also done in order to examine charge transfer between within complex. By introducing the efficient end‐capped acceptor moieties in reference molecule, enhancement in charge mobilities is noted. The large open circuit voltage, low reorganizational energies, narrower highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap, lower binding and excitation energies, and highly red shifting in absorption phenomenon indicate an efficient designing of molecules, which could be best fitted for high efficiency OSCs. Finally, theorized molecules are much superior related to their photovoltaic and electronic properties and thus are recommended to experimentalist for their synthesis and out‐looking future developments of highly efficient solar cells devices.

A Study on Characteristics of Unsaturated Sandy Soils Based on the CT Scanning Method

In the hydrologic cycle, sandy soils play the role of a connecting reservoir of surface water and groundwater, particularly in arid areas. Therefore, to provide water conservation and ecological environment protection, it is important to study the soil water behavior in the unsaturated zone. At present, the CT-scan method is commonly used to study the soil hydraulic properties. In the field of materials science, the industrial CT high-resolution instruments are applied for quantitative research on the porous microstructure and fluid filtration law in sandy soils. In this study, we have studied five samples of sand scans of the quartz sand and CUGB coarse sand types. The industrial-type CT instrument XTH225ST was used for the sample microstructure scanning. In order to identify water: air, and solid particle distribution of the sample cross section, and to analyze the particle size distribution and moisture content, the scanned images were processed using the VG-Studio and ImageJ software. Comparing the CT-scan results of the four quartz sand samples, it can be concluded that the optimal particle size, ranges from 1 to 2 mm. According to the porosity quantitative analysis, with decrease in the particle size, the total porosity grate soil sample increases. After applying the image recognition and VG- Studio software, we can see that for different particle sizes of the sand sample, the average pore size increases with increase in the particle size. To study the moisture absorption and desorption phenomenon, two samples of the CUGB coarse sand are experimentally studied. The particle size of the samples range: from 1 to 2 mm. The CT scanning analysis is used to obtain the unsaturated characteristic curve of the soil when the moisture content reaches stability. Due to the lag phenomenon, the characteristic curve of the soil moisture has an obvious “loop,” or hysteresis, shape. As shown by a 3D modeling, the distribution of capillary water in the sand column is complex, and the water flow forms multiple winding paths, like “worms” creeping in the soil. The CT-scan method is used to overcome the limitations of the traditional experimental methods and to evaluate the relationship between the moisture content and the matrix suction. The obtained characteristic curve of soil moisture can be used to improve the efficiency of technological operations. The CT-scan method provides a new way of evaluating the water distribution characteristics of unsaturated soil.

A solar simulator numerical modeling for heat absorption phenomenon research in a parabolic trough collector

A solar simulator numerical modeling for heat absorption phenomenon research in a parabolic trough collector

New device for the quality control of the high-voltage electrical insulator

During the operation of high-voltage electrical equipment, its insulation ages, its properties deteriorate, and the electrical strength decreases. To avoid sudden breakdowns of insulation and maintain the necessary level of reliability of high-voltage electrical equipment, the state of its insulation must be periodically monitored. The device described in the article is intended for preventive testing and diagnostics of heterogeneous high-voltage insulation of electric machines, power oil transformers and cables with paper-oil insulation. In particular, the integral assessment of high-voltage insulation aging, its humidification and remaining operational life can be based on the use of the absorption phenomenon (the accumulation of internal absorbed charge). Self-discharge and return voltage are measured to assess the insulation condition. A block diagram of the device for monitoring the electrical insulator quality is given as well as the formulae for determining the spent and remaining operational life of the tested insulation. The proposed device will increase the operational reliability of high-voltage electrical equipment.

Mathematical Modeling of Multilayered Skin with Embedded Tumor Through Combining Laser Ablation and Nanoparticles: Effects of Laser Beam Area, Wavelength, Intensity, Tumor Absorption Coefficient and Its Position

Laser ablation is gaining acceptance as a cancer treatment technique because of its localized energy delivery to the tumorous tissue. The combination of laser ablation with nanoparticles allows for more precise targeting of the ablative area with less damage to adjacent healthy tissue. Nevertheless, heat damage to adjacent tissue is still a potential concern. Therefore, mathematical modeling of laser-tissue interactions is a necessary part of clinical treatment planning. In this study, the temperature distribution during laser-induced thermotherapy in cancer treatment investigates using a multilayered skin (epidermis, dermis, subcutaneous fat, and muscle) with an embedded tumor model. The effects of related parameters systematically investigate; wavelength, laser intensity, beam area, tumor absorption coefficient, tumor position, tumor blood perfusion rate, and irradiation time. Mathematical modeling in this study is solved by finite element method (FEM) via COMSOLTM Multiphysics Software. Laser absorption and thermal phenomena are described by Beer-Lambert’s law and Pennes’s bioheat equation.

Zinc Oxide Quantum Dots for Organic DS Solar Cells

Sol-gel technique was adapted to synthesize Zinc Oxide quantum dots of size less than 10 nm. The tuning of median sized quantum dots can be achieved with controlled consumption of Zinc precursors. Quantum confinement has been spotted due to the phenomenon of photoluminescence and chemical absorption. The bandgap extension is in correspondence with the theory of the effective mass model. It was noticed, that the shrink in particle size resulted in an increment of the Stokes shift. The procedure of germination of quantum sized Zinc Oxide by the technique of sol-gel has been described. The processed ZnO quantum dots were further utilized as the electrode for organic dye solar cells.

Optical nonlinearities in chemically synthesized and femtosecond laser fabricated gold nanoparticle colloidal solutions

Gold nanoparticles prepared by two different methodologies, wet-chemical- citrate reduction synthesis and femtosecond laser ablation, are studied for optical nonlinearities. Femtosecond laser pulses at 800 nm wavelength are employed to study the optical nonlinear refraction and absorption through the Z-scan technique, up to 23.37 GW/cm2 laser intensities. Here we demonstrate the distinct crossovers of nonlinear absorption, from varieties of nonlinear absorption mechanisms, saturation of linear absorption, reverse saturation of absorption. The reverse saturation of absorption is primarily contributed by an initial two-photon absorption followed by three-photon absorption process. We could observe that in laser-ablated gold nanoparticles, the transition from saturable to reverse saturable absorption takes place at a lower excitation threshold compared to that in chemically produced samples. The nonlinear refraction data depicted a pronounced asymmetry for chemically synthesized samples, which could possibly be due to the dominance of absorption phenomenon. We observed that nonlinear refractive index of chemically produced samples is higher by one order of magnitude compared to those produced by laser ablation. An appealing application in optical limiting is studied, and we see that the laser-produced samples, due to their strong nonlinear absorption, serve as a suitable choice for the optical limiting application. This study provides an insight into the selection of synthesis method towards their optimized utilization in nonlinear optical domain given that we achieve particle size tunability in the two methods.

Guided Sonar-to-Satellite Translation

Underwater navigation and localization are greatly enhanced by the use of acoustic images. However, such images are of difficult interpretation. Contrarily, aerial images are easier to interpret, but require Global Positioning System (GPS) sensors. Due to absorption phenomena, GPS sensors are unavailable in underwater environments. Thus, we propose a method to translate sonar images acquired underwater to an aerial counterpart. This process is called sonar-to-satellite translation. To perform the conversion, a U-Net based neural network is proposed, enhanced with state-of-the-art techniques, such as dilated convolutions and guided filters. Afterwards, our approach is validated on two datasets containing sonar images and their satellite analogue. Qualitative experimental results indicate that the proposed method can transfer features from acoustic images to aerial images, generating satellite images that are easier to interpret and visualize.