Absorption Of Beam Research Articles

Energy Absorption and Lightweight Potential Analysis of the Front Longitudinal Beam

Different high-strength structural steel materials such as DP590, TR590, DP780, QP980, DP980, and MS1180 are tested for frontal impact in this research. The deformation modes and energy absorption characteristics of various materials and thicknesses are studied based on the trolley bump test. Then the average acceleration and the light weight potential under each structure are analyzed and compared. The research providedan optimized direction for the choice of stringer material and thickness.

Role of welding speed on keyhole-induced porosity formation based on experimental and numerical study in fiber laser welding of Al alloy

The keyhole behaviors were observed directly by laser welding experiment with quartz glass. Based on Fresnel absorption of laser beam and multi-reflection combined with volume of fluid (VOF) method, a three-dimensional mathematical model was established to study the role of welding speed on keyhole behaviors and keyhole-induced porosity formation in laser welding of aluminum alloy. The keyhole behaviors and weld pool fluid flow were discussed, and the result shows that, although the welding speed varies, the mechanism of keyhole collapse was similar. However, the keyhole stability at higher welding speed was improved due to reduced weld depth fluctuations, spatter number, keyhole depth to width ratio, and keyhole collapse frequency. Furthermore, the improved keyhole stability impeded the keyhole collapse, and the lower weld depth and solidification rate facilitated bubble escaping from the weld pool easily, which are the main factors for suppression of porosity at higher welding speed.

Transfer of optical vortices in coherently prepared media

We consider transfer of optical vortices between laser pulses carrying orbital angular momentum (OAM) in a cloud of cold atoms characterized by the $\Lambda$ configuration of the atom-light coupling. The atoms are initially prepared in a coherent superposition of the lower levels, creating a so-called phaseonium medium. If a single vortex beam initially acts on one transition of the $\Lambda$ scheme, an extra laser beam is subsequently generated with the same vorticity as that of the incident vortex beam. The absorption of the incident probe beam takes place mostly at the beginning of the atomic medium within the absorption length. The losses disappear as the probe beam propagates deeper into the medium where the atoms are transferred to their dark states. The method is extended to a tripod atom-light coupling scheme and a more general $n+1$-level scheme containing $n$ ground states and one excited state, allowing for creating of multiple twisted light beams. We also analyze generation of composite optical vortices in the $\Lambda$ scheme using a superposition of two initial vortex beams and study lossless propagation of such composite vortices.

Temperature characteristics of K-Rb hybrid optically pumped magnetometers with different density ratios.

Optically pumped magnetometers (OPMs) that are equipped with hybrid cells of K and Rb have been studied for improving their sensitivity and biomagnetic field measurements. The densities of the two alkali metal atoms and their density ratio are especially important for hybrid OPMs. In this study, we fabricated five hybrid cells using different K and Rb atom densities and measured the output signal intensities by controlling their cell temperatures. The output signal intensity of OPMs has different temperature characteristics depending on the density ratios of K and Rb atoms. The densities of the two atoms at any temperature were estimated based on the Raoult's law, and we compared the experimental results with the calculated results based on the Bloch equations. Furthermore, the numerical calculations that were obtained based on the Bloch equation by incorporating a relaxation term due to the absorption of the probe beam exhibited good agreement with the experimental results. Finally, in case of nK/nRb = 4.85, it is estimated that a sensitivity of 1.6 fT/Hz1/2 can be achieved by increasing the temperature to 270 °C.

Computer-vision-based intelligent adaptive transmission for optical wireless communication.

Optical wireless communication (OWC) has been presented as a promising candidate for future space-air-ground-ocean-integrated communication. However, the OWC is quite sensitive to the variation of the channel transmission characteristics. The light beam absorption and the scattering in the transmission media affect not only the channel feature, but also the imaging quality. Thus, there is an inherent relationship between the OWC performance and the optical imaging quality. Based on this consideration, we firstly present the idea of introducing computer vision mechanisms into the OWC systems, and then propose a computer vision-based multi-domain cooperative adjustment (CV-MDCA) mechanism's functional modules to realize the intelligent adaptive transmission in OWC systems. The CV-MDCA mechanism are specifically designed, with the emphasis on how to quantitatively determine the exact on-line channel quality from the captured images by using effective computer vision schemes. Two groups of experiments, the indoor-simulated underwater visible light communication and the outdoor-practical atmospheric free-space optics, are implemented in order to evaluate the presented CV-MDCA mechanism's performance. The results not only validate the feasibility to determine the channel quality, according to the captured channel images, but also reveal the presented three computer vision-based criteria's limitations.

Energy absorption and response speed of composite/aluminium alloy coupling bumper beam in compact electric cars

Composite materials could be applied to the bumper beam in order to enhance the structure performance and provide a light weight solution. This article assessed the impact performance of automobile bumper beams produced from composite material. First, the structural models of the bumper beams with different cross-sections were established in CAE software, and then the impact simulation was carried out. The sum of internal energy and slip energy in the bumper beams of A, B and C-type section were 140.1, 28.331 and 129.533 J, respectively. It can be concluded that the energy absorption of the collision beams with three cross-section shapes is: A-type > C-type > B-type. The simulation results are analysed from the aspects of energy absorption performance and response speed. Then, it can be seen from the simulation results that the integral crash box and separated crash box have influence on the energy absorption performance. Finally, composite specimens were produced and tested by the three-point bending test. The results showed that the specific energy absorption of 6061 aluminium alloy sample is 348.37 J. The specific energy absorption of the composite/aluminium alloy coupling sample is 359.67 J. The results showed that the energy absorption performance of the composite anti-crash beam was more satisfactory.

Ultrafast and Precision Microprocessing of Glass by Selective Absorption of Laser Beam into High-electron-density Region

Ultrafast and Precision Microprocessing of Glass by Selective Absorption of Laser Beam into High-electron-density Region

Influence of pump-beam parameters and crystal optical properties on propagation of thermally affected Bessel–Gaussian beams generated by a solid-state laser

In diode-pumped solid-state laser system, the generation and propagation of Helmholtz–Gaussian beam families such as Bessel–Gaussian (BG) beam can dramatically suffer from the effects of heat load. In this study, based on the ABCD matrix for BG beams passing through a graded-index medium, expressions for the thermal lens focal length and the output beam are obtained. Furthermore, to evaluate the impact of the pump-beam parameters and crystal optical properties, the intensity distribution of the zeroth- and first-order BG beams against radial distance together with its corresponding transverse intensity pattern on X–Y plane under different pump powers, pump beam waists, absorption coefficients, and thermal conductivities are simulated and compared. The simulation results indicate that for powerful narrow pump beam, the thermal-induced effects are so dramatic that the intensity profiles are altered, as the discernment of BG beams is not easily feasible; however, taking into account the large pump waist, high thermal conductivity and small absorption coefficient can partly cause the laser output similar to non-thermal one despite high pumping power is received. Therefore, the precise selection of laser parameters can considerably reduce the effects of induced heat on the generation and propagation of BG beams. The obtained results are a valuable hint to experimenters for beam identification and beam quality monitoring.

Micron-sized PFOB liquid core droplets stabilized with tailored-made perfluorinated surfactants as a new class of endovascular sono-sensitizers for focused ultrasound thermotherapy.

The purpose of this study was to develop micron-sized droplet emulsions able to increase the heat deposition of high intensity focused ultrasound (HIFU), aiming to accelerate the tumour ablation in highly perfused organs with reduced side effects. The investigated droplets consisted of a perfluorooctyl bromide (PFOB) core coated with a biocompatible fluorinated surfactant called F-TAC. The novelty of this work relies on the use, for this application, of a high boiling point perfluorocarbon core (142 °C), combined with an in-house fluorinated surfactant to formulate the emulsion, yielding quasi-reversible strong interactions between the HIFU beam and the droplets. In order to fine-tune the emulsion size, surfactants with different hydrophobic/hydrophilic ratios were screened. Different concentrations of PFOB droplets were homogeneously embedded in two different MRI compatible materials, exhibiting either ultrasound (US) absorbing or non-absorbing properties. For the US absorbing TMM, the speed of sound at each droplet concentration was also assessed. These TMM were sonicated by 1 MHz HIFU with acoustical power of 94 W at two different duty cycles. The temperature elevation was monitored accurately by MRI proton shift resonance frequency in near real-time. The presence of sono-sensitive droplets induced a significant increase of the HIFU thermal effect that persisted under repeated sonication of the same locus. Optimal enhancement was observed at the lowest concentration tested (0.1%) with an additional temperature rise at the focal point of approximately 4 °C per applied kJ of acoustic energy corresponding to one order of magnitude augmentation of the thermal dose. Furthermore, no deformation of the heating pattern pre- or post-focal was observed.

Controllable transmission of vector beams in dichroic medium**Project supported by the National Natural Science Foundation of China (Grant Nos. 11774286, 11374238, 11534008, 11604258, and 11574247), China Postdoctoral Science Foundation (Grant No. 2016M592771), and the Fundamental Research Funds for the Central Universities, China (Grant No. xjj2018213).

Vector beams with spatially varying polarization distribution in the wavefront plane have received increasing attention in recent years. The manipulation of vector beams both in intensity and polarization distributions is highly desired and under development. In this work, we study the transmission property of vector beams through warm rubidium vapor and realize controllable transmission of vector beams based on atomic dichroism. By utilizing the linearly polarized beam and vector beams as the pump and probe beams in a pump–probe configuration, a spatially-dependent dichroism can be obtained, which leads to spatially varied absorption of the probe beam. The controllable intensity distribution of the probe beam, as a two-petal pattern, can rotate with the variation of the pump beam’s polarization states. We experimentally demonstrate the mechanism of dichroism with linear polarization light and provide an explanation based on the optical pumping effect. Alternatively, the varying trend of the probe beam’s intensity is also interpreted by utilizing the Jones matrix. Our results are thus beneficial for providing potential applications in optical manipulation in atomic ensembles.

Picosecond laser drilling of silicon with applied voltage

The short pulse duration of a picosecond laser (ps) leads to high peak power and ablates materials with much reduced thermal effects. Commercial ps lasers generate high-repetition-rate pulses and become more accepted as a major tool for material removal applications. However, most of the commercial ps lasers emit pulses at infrared (IR) wavelengths with photon energy close to the Si band gap energy of 1.1 eV. The corresponding optical absorption coefficient is low. To improve the laser beam absorption in Si, several methods have been investigated. For instance, it is reported that the material removal efficiency has been improved by raising the substrate temperatures during laser drilling due to the enhancement of the Si absorption coefficient. However, such approach may result in reduction in machining accuracy due to thermal expansion of the substrate. In this paper, we propose a new method by applying a direct current (DC) across a silicon substrate during the ps laser drilling process. The externally applied voltage potential would lead to more aligned movement of free electrons and therefore increase electrical current flow in the silicon substrate. The hypothesis of this study is that more free electrons are made available in the Si substrate for collisions with the laser photons, which increases the Si absorption coefficient of the laser beam. It was found that the material removal is markedly improved with the assistance of the electrical current flow. The entrance hole diameter increased by 14% and the exit hole diameter increased by 90% when the current in the Si substrate was subjected to a fixed current of 0.5 A. However, a larger amount of material debris covering an enlarged surface area was observed under the applied DC voltage. The possible reasons for such observations are discussed based on the enhanced laser energy absorption as the result of the presence of electrical current in the Si substrate.

RETROFITTING OF RC BEAMS USING ULTRA HIGH PERFORMANCE FIBER REINFORCED CONCRETE

Shear deficient structures have been strengthened or repaired by using various methods, e.g., external pre-stressing, shotcreting, steel plate bonding, polymer impregnation, fiber reinforced polymers (FRPs). But there were problems with each of the above techniques as the use of FRP gives sudden failure due to de-bonding, steel plates got corroded after some time and several losses in the case of external pre-stressing. To overcome all the above problems faced in different retrofitting techniques, a new cementitious material with ultra high performance characteristics like very high compressive strength (above 110 MPa), high tensile and flexural strength due to the addition of fibers, very less permeable and high workability i.e. UHP-FRC came into existence. In the present study, shear deficient RC beams initially stressed to a prefixed percentage, i.e. 60% of the ultimate failure load are retrofitted using UHP-FRC. Retrofitting is done using side face retrofitting. From the study it is seen that the ultimate load carrying capacity of RC beams retrofitted with UHP-FRC is significantly increased with side face retrofitting. Moreover, this technique also increased the ductility and energy absorption of RC beams which resulted in the usefulness of UHPFRC as a retrofitted material.

Electron beam irradiation effect on the mechanical and thermal properties of 2-D silk fibroin fabric/poly(lactic acid) biocomposites

Silk fibroin fabrics (SFF) were irradiated at various electron beam absorption doses. The irradiation effect on the breaking properties of SFF, the fiber topography, and the tensile, flexural and dynamic mechanical properties of 2-directional SFF/poly(lactic acid) (PLA) biocomposites were explored. The irradiation at 10kGy was most effective not only to increase the SFF breaking properties, but also to enhance the mechanical and thermal properties of SFF/PLA biocomposites. The microscopic analysis of fractured surfaces supported the irradiation dependence of the mechanical and thermal data, showing the increased interfacial bonding between the silk fiber and the PLA, particularly at 10kGy.

Overview of Laser Absorptivity Measurement Techniques for Material Processing

During laser surface treatment, the beam absorption can vary considerably depending on the surface quality, temperature and environment. The metallic surfaces exhibit higher absorptivity when irradiated with a focused laser light. Investigation of the dynamic variation of absorptivity of metals during laser processing is a topic of interest for manufacturing community. This paper focuses on a brief review of absorptivity measurement methods adopted for industrial metals such as steel, titanium, aluminium and copper during laser surface treatment processes. It provides state of art in analytical, numerical and experimental techniques for measuring the absorptivity in order to design an efficient laser control systems.

Azimuthal modulation of electromagnetically induced transparency using structured light.

Recently a scheme has been proposed for detection of the structured light by measuring the transmission of a vortex beam through a cloud of cold rubidium atoms with energy levels of the Λ-type configuration [N. Radwell et al., Phys. Rev. Lett.114, 123603 (2015) ]. This enables observation of regions of spatially dependent electromagnetically induced transparency (EIT). Here we suggest another scenario for detection of the structured light by measuring the absorption profile of a weak nonvortex probe beam in a highly resonant five-level combined tripod and Λ (CTL) atom-light coupling setup. We demonstrate that due to the closed-loop structure of CTL scheme, the absorption of the probe beam depends on the azimuthal angle and orbital angular momentum (OAM) of the control vortex beams. This feature is missing in simple Λ or tripod schemes, as there is no loop in such atom-light couplings. One can identify different regions of spatially structured transparency through measuring the absorption of probe field under different configurations of structured control light.

Flexural behaviour and theoretical prediction of lightweight ferrocement composite beams

Sixteen full-scale simply supported composite beams of the same dimensions, breadth = 100 mm, thickness, 200 mm, and length of 2000 mm, subjected to flexural loading, were experimentally tested and their structural parameters, namely, pre-crack stiffness, serviceability loads, post-cracking loads, energy absorption, ultimate load-to weight ratio, and compressive strains were investigated. In addition, theoretical prediction of ultimate loads was carried out to adopt a theoretical approach as a design methodology for ferrocement elements. Experimental results showed that pre-crack stiffness, maximum service loads, maximum values of energy absorption and ultimate loads to weight ratios of ferrocement beams are higher than that of lightweight control beam by up to 46%, 32%, 64.4% and 32.8%, respectively. Higher post-cracking loads were exhibited by beams reinforced by expanded metal mesh, compared to those reinforced by welded wire mesh regardless of the core filling type. For post cracking load indicator, confinement with expanded metal mesh was the decisive factor affecting the post-cracking load capacity. Beams reinforced with expanded metal mesh showed higher energy absorption than those of the other beams reinforced with welded wire mesh or fiberglass mesh. Increasing the amount of mesh reinforcement results in higher energy absorption for beams made of Autoclaved Aerated Lightweight Brick Core (AAC). Generally, the maximum compressive strains of the ferrocement composite beams were generated at higher loads compared to those of the control beams. Theoretical calculations, based on the assumption of strains and forces distribution block, results in acceptable prediction of the ultimate loads. The ratio of experimental to theoretical ultimate loads ranges from 0.91 to 1.26. This study showed that ferrocement composite beams may be used as an alternative to traditional reinforced normal or lightweight concrete beams after careful choice of the combination of core and mesh types to suit the application in question.

A spectroscopic electric field vector imaging diagnostic for electron cyclotron heating systems.

An experimental measurement of the wave electric field vector provides important data that can be used to directly compare against 3D full-wave simulations. This direct comparison yields the fastest approach toward identifying missing physics in computational models and providing a high fidelity validation platform. In this paper, we present a diagnostic that is capable of imaging the Electron Cyclotron (EC) wave electric field vector by acquiring filtered images of polarized D β spectral satellites. The diagnostic is designed to have a spatial and temporal resolution on the order of 100 μm and 100 μs, respectively. The diagnostic purpose is to provide experimental data for the direct validation of full-wave codes used to predict EC beam propagation and absorption and to provide real-time monitoring of EC waves.

Light-induced hydrodynamic reorientation of hybrid aligned nematic liquid crystals caused by direct volume expansion

ABSTRACTThe dynamics of the direct volume expansion mechanism of light-induced hydrodynamic motions in hybrid-oriented nematic liquid crystal (NLC) have been studied experimentally. It was shown that heating caused by the absorption of a laser beam results in expansion of a NLC volume and induces hydrodynamic flow in a planar capillary. The hydrodynamic flow reorients the NLC molecules and thus the optical properties of the NLC layer are changing. A change of the tilt direction of the NLC director is demonstrated experimentally, and it is shown that hybrid-oriented NLC could be considered as ‘flexible ribbon’. Velocity gradient brings about an increase of curvature when hydrodynamic flow velocity is directed out of the ‘flexible ribbon’s’ curvature. The ‘flexible ribbon’ reverses its curvature when velocity is directed into ‘flexible ribbon’s’ curvature.

Two-dimensional full-wave simulation of propagation and absorption of a microwave beam in magnetized plasma

Results from solving a full-wave two-dimensional model problem on the propagation and absorption of a microwave beam in plasma for the magnetic configuration of the L-2M stellarator are presented. The coefficients of transmission and reflection are calculated. The distributions of the microwave power absorbed in plasma are obtained. It is found that, under conditions typical of L2-M experiments on ECR plasma heating at the second harmonic of the electron gyrofrequency, an appreciable fraction (about 10%) of the incident microwave power can be deflected downward from the plasma axis, not reaching the absorption region. The fraction of the downward-deflected microwave power is shown to increase considerably at central plasma densities close to the cutoff density (ne ≈ (0.8–0.9)ncut). The simulation results are compared with results of calculations by the ray-tracing method.

Dolphin and bat sonar: Nonlinear acoustic effects

Both dolphin and bat sonars operate in an amplitude and frequency regime where nonlinear effects can be observed, particularly distortion and the generation of harmonics. Computations illustrating these nonlinear effects are presented, quantifying effects that could be observed in experiments on echolocating signals conducted with wideband sensors. The mathematical model used is the Khokhlov-Zabolotskaya-Kuznetsov (KZK) nonlinear parabolic wave equation, which includes diffraction and absorption for directional beams, with computations performed in the time domain using a finite-difference scheme. Inputs to the computations are sample dolphin echolocation transients (clicks) and bat echolocation tone bursts (FM Chirps—fundamental component), taken from the literature for a few species of high-amplitude emitters. Calculations begin in the water or air media. Propagating high-amplitude dolphin clicks are shown to distort, create harmonics, and suffer nonlinear attenuation at ranges of tens of meters. Propagating high-amplitude bat chirps are shown capable of undergoing some nonlinear distortion at ranges within 10 m. The results may be useful in understanding the significance of nonlinear effects for work with these animals. (Work supported by ARL:UT Austin.)