Focusing Properties Research Articles

Effect of Plasma Argon Pretreatment on the Surface Properties of AZ31 Magnesium Alloy

Climate change has evidenced the need to reduce carbon dioxide emissions into the atmosphere, and so for transport applications, lighter weight alloys have been studied, such as magnesium alloys. However, they are susceptible to corrosion; therefore, surface treatments have been extensively studied. In this work, the influence of argon plasma pretreatment on the surface properties of an AZ31 magnesium alloy focus on the enhancement of the reactivity of the surface, which was examined by surface analysis techniques, electrochemical techniques, and gravimetric measurements. The samples were polished and exposed to argon plasma for two minutes in order to activate the surface. Contact angle measurements revealed higher surface energy after applying the pretreatment, and atomic force microscopy showed a roughness increase, while X-Ray photoelectron spectroscopy showed a chemical change on the surface, where after pretreatment the oxygen species increased. Electrochemical measurements showed that surface pretreatment does not affect the corrosion mechanism of the alloy, while electrochemical impedance spectroscopy reveals an increase in the original thickness of the surface film. This increase is likely associated with the high reactivity that the plasma pretreatment confers to the surface of the AZ31 alloy, affecting the extent of oxide formation and, consequently, the increase in its protection capacity. The weight loss measurements support the effect of the plasma pretreatment on the oxide thickness since the corrosion rate of the pretreated AZ31 specimens was lower than that of those that did not receive the surface pretreatment.

Generation of three-dimensional polarization-controlled tunable multiplex focused optical vortex and vector vortex beams via liquid crystal geometric phase

Optical vortex beams carrying the orbital angular momentum (OAM), especially vector vortex beams, play essential roles in many fields such as optical communication and optical manipulation. In recent years, focusing and multiplexing optical vortex beams have attracted significant interest and become important research topics. In this study, a new type of liquid crystal geometric phase optical element is demonstrated to achieve multiplex focused optical vortex (FOV) beams. The 3D coordinates and the topological charges of each FOV in arrays can be customized on demand. Meanwhile, the distribution of arrays can be switched by the polarization of the incident light. Furthermore, the liquid crystal element is modified to generate multiplex focused vector vortex beams (FVVBs) based on the superposition of multiple OAM states. Similarly, the positions, the Pancharatnam topological charges, and the polarization orders of FVVBs can be preset as required. Besides, the polarization direction of incidence controls the polarization states of the generated FVVBs. This research achieves customized polarization-controlled multiplex FOVs and FVVBs with both multichannel and focusing properties, providing more flexibility for applications.

Comparative Study of Numerical Methods for Solving the Fresnel Integral in Aperiodic Diffractive Lenses

In this work, we present a comparative analysis of different numerical methods to obtain the focusing properties of the zone plates based on Fibonacci and Cantor sequences. The Fresnel approximation was solved numerically in order to obtain the axial irradiance provided by these diffractive lenses. Two different methods were applied. The first one is based on numerical integration, specifically the Simpson integration method and the two-dimensional Gaussian quadrature. The second consisted in the implementation of the Fast Fourier Transform in both one and two dimensions. The axial irradiance of the lenses, the relative error with respect to the analytical solution, and the calculation time required by each method are analyzed and compared. From this analysis it was concluded that the Gauss method presents the best balance between accuracy and computation time. This analysis could be useful to decide the most convenient numerical method to be used for the study of more complex diffractive structures.

Pixel‐Level Grayscale Manipulation to Improve Accuracy in Digital Light Processing 3D Printing

AbstractDigital light processing (DLP) is a widely used additive manufacturing technique for functional applications due to its high accuracy and print speeds. However, a variety of factors such as pixel size, motion stage resolution, optical focus, and chemical properties of the resin limit DLP's minimum resolution. Recently, research into locally varying light intensities has led to the emergence of grayscale DLP printing, which offers new capabilities including sub‐pixel manipulation of the printed shape. Here, a methodology is developed to enhance accuracy beyond what is typically capable for a given projector resolution by using pixel‐level grayscale control to create round features from sharp pixels. A numerical representation of the DLP pixel shape is developed to account for the effects of the incident light patterns. A reaction‐diffusion model is then used to predict the printed shapes before and after grayscale enhancement. This model is used to determine the optimal pixel intensities to match a target shape. Finally, the minimum feature size allowed by the proposed method is explored. The promising results represent an important step forward in raising DLP printing to higher accuracy, which will allow the fabrication of functional and structural components with smaller features or smoother faces.

Generation and control of the circle Olver beams.

The circle Olver beams (COBs) generated by modulation on the basis of a new type of Olver beam are presented numerically and experimentally. The zeroth order COB is the circle Airy beam. We demonstrate auto-focusing of the COBs with both inward and outward accelerations, where the odd order COBs display auto-defocusing while the even order COBs (ECOBs) tend to focus more abruptly. We also explore the effect of the decay factor and the scaling factor on the beams' focusing properties, such as the initial energy distribution, the focusing position, the focusing intensity and the focusing depth, by using the parity mode. In addition, we verify the self-healing property of the COBs. Finally, we set up an experimental platform to implement particle capture and manipulation with the ECOBs. Our results offer practical applications for particle manipulation, laser processing, etc.

Accelerating superluminal laser focus generated by a long-focal-depth mirror with high numerical aperture.

The long-focal-depth mirror is a novel reflective element proposed in recent years. Due to the advantages of negligible dependence on wavelength and high damage threshold, it is suitable to focus ultra-short laser pulses with broadband spectra and high intensity with a focal depth of centimeter scale. To the best of our knowledge, the focusing properties of this mirror has been only studied under low numerical aperture (NA). In this paper, we extend it to the case of high NA and it is proved that an accelerating superluminal laser focus can be always generated by this extension, in which the degree of acceleration increases with the increase of NA. And the velocity of laser focus increases approximately linearly from c to 1.6c for NA = 0.707. Due to its properties of tight focusing, the Richards-Wolf integrals have been used to study the intensity distribution of each polarization component for different kinds of incident light. And these are linearly polarized light, radially polarized light, azimuthally polarized light, linearly polarized light with spiral phase, and linearly polarized light with ultrashort pulses. From comparisons of numerical results, the intensity distributions are obviously different for different kind of incident light, and accelerating superluminal laser focus with special structure (such as the hollow conical beam) can be produced under appropriate condition. We believe this study can expand the fields of application for the long-focal-depth mirror.

Hybrids of Ixodes ricinus and Ixodes persulcatus ticks effectively acquire and transmit tick-borne encephalitis virus.

Ixodes rici nus and Ixodes persulcatus ticks are the main vectors of tick-borne encephalitis virus (TBEV), which has three main subtypes connected with certain tick species: the European subtype, associated with I. ricinus, and the Siberian and Far-Eastern subtypes, associated with I. persulcatus. Distribution ranges of these species overlap and form large sympatric areas in the East European Plain and Baltic countries. It has previously been shown that crossing of I. ricinus and I. persulcatus is possible, with the appearance of sterile hybrids. Hybridization of ticks can affect not only the spread of ticks but also the properties of natural foci of arbovirus infections, in particular TBEV. In the present study, we analyzed the effectiveness of virus transmission from infected mice to larvae and nymphs and trans-stadial transmission (from larvae to nymph and adult) in I. ricinus, I. persulcatus, and hybrids. For this purpose, we bred a hybrid generation from the crossing of I. persulcatus females and I. ricinus males, and we used the Siberian and European subtypes of TBEV. We showed that after feeding on infected mice, virus prevalence in engorged ticks decreased over time, and after molting, the opposite was true. In hybrids we observed the highest acquisition effectiveness and RNA copy numbers during Siberian TBEV subtype transmission. The efficiency of trans-stadial transmission of both TBEV subtypes was similar in hybrids and parental species. After the second trans-stadial TBEV transmission, a significant increase in ticks' infection rates was observed only in specific subtype-tick combination. Our data demonstrate the possible features of TBEV circulation in the I. ricinus and I. persulcatus sympatry area.

Development of a Metalens for Radio Wave Ground-Penetrating Radars

This article discusses the possibility of using a metamaterial to focus radiation from an antenna for GPR. Composite ring conductors were used as a material for focusing radiation at frequencies of 0.5–3 GHz. The modeling of the matrix structure is presented, and the electric component of the field is considered when using a four-layer structure with a thickness of about 5 cm. Experimental studies of the focusing properties of the metamaterial and the possibility of its use in ground-penetrating radar are presented. Using the developed system, an object was detected at different depths, and the superiority of the metamaterial in relation to the use of a focusing system based on a parabolic mirror is shown.

Tunable THz flat zone plate based on stretchable single-walled carbon nanotube thin film

Tunable optoelectronics have attracted a lot of attention in recent years because of their variety of applications in next-generation devices. Among the potential uses for tuning optical elements, those allowing consistent parameter control stand out. We present an approach for the creation of mechanically tunable zone plate lenses in the THz range. Our devices comprise single-walled carbon nanotube (SWCNT) thin films of predetermined design integrated with stretchable polymer films. These offer high-performance and in situ tunability of focal length up to 50%. We studied the focusing properties of our lenses using the backward-wave oscillator THz imaging technique, supported by numerical simulations based on the finite element frequency domain method. Our approach may further enable the integration of SWCNT films into photonic and optoelectronic applications and could be of use for the creation of a variety of flexible and stretchable THz optical elements.

Investigation of focusing properties of photovoltaic module concentrator in a wide temperature range

In the current work properties of a solar radiance concentrator with Fresnel lens made of Elastosil RT604 silicon made by Wacker have been investigated. The dependence of concentrator focal distance on temperature has been determined. Impact of variation of temperature-dependent concentrator focusing properties on the magnitude of short current of photovoltaic submodule has been determined by direct measurements using solar simulator. Using formalized model of modules based on the studied concentrator and solar cells with three and six p-n- junctions dimensions of a solar image in a wavelength range corresponding to an absorption profile of individual p-n- junctions has been calculated for the temperature range 10-60oC. It has been concluded that in the case of three p-n- junctions the minimum size of solar image at focal plane was 4.7 mm with the distance between the concentrator and solar cell being equal to 106.25 mm, and in the case of six p-n- junctions, the minimum size was 4.8 mm with the distance between concentrator and solar cell being equal to 106.5 mm. Keywords: silicone lens, Wacker RT604, concentrator photovoltaic module, multijunction solar cells.

Исследование фокусирующих свойств концентратора фотоэлектрического модуля в расширенном температурном диапазоне

Abstract: In the current work properties of a solar radiance concentrator with Fresnel lens made of Elastosil RT604 silicon made by Wacker have been investigated. The dependence of concentrator focal distance on temperature has been determined. Impact of variation of temperature-dependent concentrator focusing properties on the magnitude of short current of photovoltaic submodule has been determined by direct measurements using solar simulator. Using formalized model of modules based on the studied concentrator and solar cells with three and six p-n junctions dimensions of a solar image in a wavelength range corresponding to an absorption profile of individual p-n junctions has been calculated for the temperature range 10-60 C. It has been concluded that in the case of three p-n junctions the minimum size of solar image at focal plane was 4.7 mm with the distance between the concentrator and solar cell being equal to 106.25 mm, and in the case of six p-n junctions, the minimum size was 4.8 mm with the distance between concentrator and solar cell being equal to 106.5 mm.

A New Method for Determining the Size of a Synchrotron Radiation Beam in the Focus of a Compound Refractive Lens

A new method is proposed for determining experimentally the size of a synchrotron radiation beam in the focus of planar compound refractive lenses. The method consists in measuring the angular divergence of radiation after the focus using Bragg diffraction in a perfect crystal during its rotation. This method determines the beam size, which depends only on the focusing properties of the lenses in use, in contrast to other currently applied methods. The efficiency of the proposed approach has been experimentally demonstrated using nanofocusing planar silicon lenses as an example.

Time-inversion technique based correction of complex radome radiation beam distortion

In the electromagnetic wave radiated by radome, there often occur pointing angle deviation, beam distortion and other phenomena, due to the complex electromagnetic medium composition, special contour and complex working environments. For conventional optimization methods, harsh and complex situations increase its workload, especially in the case that the specific location parameter information is unknown. In this paper, a method with time-inversion technique for correcting the radiation beam distortion of the complex radome is proposed. With the time-inversionl method, the concrete parameters of different positions for the radome and the surrounding environment information are not necessary to be determined in advance. The derivation shows that the environmental information is eliminated adaptively by the conjugate convolution operation, and it is proved by numerical operation that the signal of maximum radiation gain in target angle is time-inversion signal. Then based on the adaptive focusing properties of time-inversion electromagnetic waves, a top wedge radome and an icing working radome are taken as the case study. The equal amplitude phase shifting serves as the control group to highlight the advantages of time-reversal. In the end, the results show that the radiation beam pointing error can be reduced from ±10° to ±0.9° within ±45° scanning range for the top wedge radome in C-band. And the annihilated main beam can be converged again for the radome in the icing state. In addition, all the improvements are in a broadband range, and the robustness of the entire radome system is enhanced by increasing target angle energy caused by the increasing the directionality of the array radiation and the narrowing the 3 dB beamwidth. This paper provides an effective method of analyzing the complex radomes and radio wave propagations in complex media.

Influence of fabrication conditions on the structural characteristics and the magnetic properties of FeAl2O4

AbstractWe report a systematic evaluation of the magnetic properties of FeAl2O4 focusing on the relationship between the fabrication conditions and its structural characteristics, in order to improve ceramics processing in applications of this material. For this purpose, the most important factor to control is the inversion parameter, expressed as y in the (Fe1−yAly)(Al1−y/2Fey/2)2O4 composition, which is relatively high for the spinel aluminate of a transition metal. The magnetic properties of these samples all show the spin glass phenomenon at low temperatures, and the cusp temperature depends systematically on this y value. This means that the evaluation of these magnetic properties will be an effective way to predict some characteristics of product FeAl2O4. Additionally, this study found an anomaly in the structural and magnetic characteristics of FeAl2O4 fabricated at a low temperature. This is thought to originate in a tiny and a small amount of impurity. It will be key for discussing the quality of chemically synthesized FeAl2O4, which is typically produced at low temperatures.

On the curvature invariants of the massive Banados–Teitelboim–Zanelli black holes and their holographic pictures

In this paper, the curvature structure of a ([Formula: see text])-dimensional black hole in the massive-charged-Born–Infeld gravity is investigated. The metric that we consider is characterized by four degrees of freedom which are the mass and electric charge of the black hole, the mass of the graviton field, and a cosmological constant. For the charged and neutral cases separately, we present various constraints among scalar polynomial curvature invariants which could invariantly characterize our desired space–times. Specially, an appropriate scalar polynomial curvature invariant and a Cartan curvature invariant which together could detect the black hole horizon would be explicitly constructed. Using algorithms related to the focusing properties of a bundle of light rays on the horizon which are accounted for by the Raychaudhuri equation, a procedure for isolating the black hole parameters, as the algebraic combinations involving the curvature invariants, would be presented. It will be shown that this technique could specially be applied for black holes with zero electric charge, contrary to the cases of solutions of lower-dimensional nonmassive gravity. In addition, for the case of massive ([Formula: see text])-dimensional black hole, the irreducible mass, which quantifies the maximum amount of energy which could be extracted from a black hole would be derived. Therefore, we show that the Hawking temperatures of these black holes could be reduced to the pure curvature properties of the space–times. Finally, we comment on the relationship between our analysis and the novel roles it could play in numerical quark–gluon plasma simulations and other QCD models and also black hole information paradox where the holographic correspondence could be exploited.

ASSESSMENT OF THE POSSIBILITY OF MODERNIZING A SPACE CHARGE LENS FOR FOCUSING BEAMS OF NEGATIVE HYDROGEN IONS DUE TO CONFINEMENT OF POSITIVE BACKGROUND IONS BY AN ALTERNATING ELECTRIC FIELD

The work is devoted to considering the possibility of improving the focusing properties of a space charge lens due to charge retention of positive ions by an electric field that varies both in time and along the axis of the system. Numerical calculations of motion trajectories of positive argon ion during interaction with an alternating electric field with oscillation frequencies in the range of 1...8 MHz and amplitude in the range of 1.5...6 kV were carried out. A significant increase in the residence time of positive argon ion in the overcompensated beam of negative hydrogen ions is shown, which indicates the possibility of significant influencing focusing charge in the lens for focusing beams of negative hydrogen ions.

A reflectionless compact elliptical half Maxwell fish-eye lens designed by transformation optics

A two-dimensional half Maxwell fish-eye lens is compressed using a linear transformation that maps a half circle to a half ellipse. The focusing property of the lens is preserved while making the device more compact. The boundary reflections, investigated for both TE and TM polarizations, were suppressed for beams directed toward the optical axis of the lens. A designed prototype provided a scanning range of ±20° with negligible reflections. The design’s functionality was verified using COMSOL multiphysics.

Constructing spin-structured focal fields for chiral-sensitive trapping with dielectric metalens

Engineering the chiral field is crucial for the flexible manipulation of chiral particles. Some complex optical setups for constructing spin-structured fields have been well developed to sort particles with opposite chiralities toward opposite transversal directions. In this work, we demonstrate the robust construction of a class of focal fields that possess laterally variant optical spin angular momentum by using the monolayer dielectric metalens. By utilizing the simultaneous modulation capacity of the phase and polarization of the dielectric metalens, we can establish a line focus with laterally tailored gradient optical helicity. The focusing property of this metalens and the polarization structure of the focal field are theoretically analyzed using a hybrid vector-focusing model and experimentally demonstrated by NA = 0.2 and 0.5 samples. We illustrate that this type of gradient helicity offers opportunities to induce a chirality-sensitive lateral force for chiral particles.

An innovative optical element for X-ray beam aperture, monitoring, and diagnostic at the CARNAÚBA beamline at SIRIUS/LNLS

The CARNAÚBA beamline is the tender-to-hard X-ray nanoprobe under commissioning for the new source Sirius at the Brazilian Synchrotron Light Laboratory (LNLS). The all-achromatic optics relies on horizontal deflection mirrors, a horizontal secondary source aperture (SSA), and Kirkpatrick–Baez (KB) mirrors to reach beam size down to ~30x30 nm2 at the sample position. To handle the highly focused power density of the pink beam and reach the desired stability for the horizontal secondary source, essential for the desired focusing and coherent properties at the sample position, we present here an SSA device based on a cryogenically cooled Si crystal in a channel-cut geometry. The crystal slabs define the channel aperture, which is controlled by a fine rotation. Simultaneously to the aperture function, the device plays the key role of beam position monitor and beam diagnostic. The scattered signal from the slabs is used to monitor the horizontal beam position during experiments and serves as a feedback input for the pitch control system of the upstream focusing mirror to stabilize the beam intensity and wavefront. The Bragg magnifier geometry of the device spreads the beam over the slabs, allowing the diffracted image of the beam to be collected by an area detector. The beam spread on the slabs also reduces the power density reaching the device, keeping it stable and under controlled temperatures.

Analysis of infrared nanojets with self-focusing nonlinearities

We present a numerical study of the linear and nonlinear diffraction and focusing properties of dielectric metasurfaces consisting of silicon microcylinder arrays resting on a silicon substrate. Upon diffraction, such structures lead to the formation of near-field intensity profiles that are reminiscent of photonic nanojets and propagate in a similar fashion. The generation and propagation of these photonic jets were analyzed under high intensity mid-infrared illumination conditions for which the third-order optical nonlinearity of silicon leads to pronounced self-focusing effects. The illumination wavelength of 3388 nm was selected to be below the two-photon absorption edge. Our results indicate that the Kerr nonlinear effect enhances light concentration throughout the generated photonic jet with an increase in intensity of about 20% compared to the linear regime for the power levels considered in this work. In all cases, the transverse beamwidth remains subwavelength, and the nonlinear effect reduces the full width half maximum size by 100 nm for both electric field intensity and the longitudinal Poynting vector.