Amplitude Profile Research Articles

Complex-amplitude modulation of surface waves based on a metasurface coupler.

Simultaneous and independent modulation of the amplitude and phase of surface waves (SWs) is critical in photonics and plasmonics. Here, we propose a method for flexible complex-amplitude modulation of SWs based on a metasurface coupler. Benefiting from the full range complex-amplitude modulation ability of the meta-atoms over the transmitted field, the coupler can convert the incident wave into a driven surface wave (DSW) with an arbitrary combination of amplitude and initial phase. By placing a dielectric waveguide that supports guided SWs below the coupler, the DSWs can resonantly couple to SWs while preserving complex-amplitude modulation. The proposed scheme provides a practical way for freely tailoring the phase and amplitude profiles of SWs wavefronts. As verification, meta-devices for normal and deflected SW Airy beam generation and SW dual focusing are designed and characterized in the microwave regime. Our findings may stimulate various advanced surface optical meta-devices.

Analytical investigation of trapped waves over a submerged exponential ridge

Based on the linear shallow-water equations, analytical solutions for trapped waves over an asymmetric oceanic ridge with an exponential cross-sectional profile are presented. The solutions can become those for a symmetric ridge by setting the same topographic parameter for both sides, in which there are both symmetric and asymmetric trapped waves. The dispersion relationships imply that the wavenumber is related to not only the frequency and water depth at the top of the ridge but also the cross-section profile parameters and the mode number. With increasing frequency, the phase velocity decreases rapidly and approaches the classical shallow-water wave velocity for fixed water depth at the top and profile parameters. Meanwhile, for increasing angular frequency, the energy velocity first increases sharply from less than the shallow-water wave velocity and then decreases gently toward it. For an asymmetric ridge, the amplitude profile is confined to a narrower region on the steeper side and spread in a wider region on the less-steep side. Finally, the analytical solutions are applied to reveal the trapping effect of the Hawaii ridge on the 2011 Tohoku Tsunami in the North Pacific.

Highly Stable Vibration Measurements by Common-path off-axis Digital Holography

Measurements of vibration and dynamic deformation with high resolution and accuracy by non-destructive techniques are of great interest in many branches of engineering. We report a non-destructive method based on digital holographic interferometry for high-precision micro-vibration measurement of a 3D object. Herein, a new and simple configuration of a common-path off-axis digital holographic system, with high mechanical stability and compact in size, is proposed. The simplicity, compactness, and high stability of the proposed setup are provided by employing a wedge plate in-line with the test object to create a clean reference beam. The object and reference beams propagate the same path, without the need for any specialized optical component or arrangement, and these beams allow to interfere on the faceplate of the image sensor to form a digital hologram. The feasibility of the proposed system is demonstrated by measuring the vibration of the objects driven by different excitation signals. A series of digital holograms of a vibrating object is recorded by the use of a high-speed image sensor. The result of the reconstruction of the recorded holograms is an array of complex numbers containing the complete amplitude and phase profile of the object, which in turn provides displacement and vibration information. Due to its simple geometry and significant outcomes, the proposed system could be established as a powerful tool for a wide range of optical imaging and measurement investigations.

Ultra-wideband two-dimensional Airy beam generation with an amplitude-tailorable metasurface.

Airy beams, accelerating optical beams with exotic properties of self-bending, self-healing and non-diffraction, are essential for a wide range of photonics applications. Recently, metasurfaces have provided an efficient platform for generating desired Airy beams within a thin thickness, but they suffer from the narrow bandwidth, especially for two-dimensional (2D) Airy beams. Here, we propose an amplitude-tailorable polarization-converting metasurface to enable ultra-wideband 2D Airy beam generation. The amplitude and phase profiles for the 2D Airy beam can be realized by tuning only the orientation of the multi-resonant meta-atom, which can operate in the range of 6.6 GHz to 23.7 GHz, or fractional bandwidth of 113%. An exemplary prototype is measured to validate the design principle, which is in agreement with the simulation results. The proposed method holds great promise for wavefront shaping, and may facilitate the uses of Airy beam for practical applications.

Direct field-to-pattern monolithic design of holographic metasurface via residual encoder-decoder convolutional neural network

Complex-amplitude holographic metasurfaces (CAHMs) with the flexibility in modulating phase and amplitude profiles have been used to manipulate the propagation of wavefront with an unprecedented level, leading to higher image-reconstruction quality compared with their natural counterparts. However, prevailing design methods of CAHMs are based on Huygens-Fresnel theory, meta-atom optimization, numerical simulation and experimental verification, which results in a consumption of computing resources. Here, we applied residual encoder-decoder convolutional neural network to directly map the electric field distributions and input images for monolithic metasurface design. A pretrained network is firstly trained by the electric field distributions calculated by diffraction theory, which is subsequently migrated as transfer learning framework to map the simulated electric field distributions and input images. The training results show that the normalized mean pixel error is about 3% on dataset. As verification, the metasurface prototypes are fabricated, simulated and measured. The reconstructed electric field of reverse-engineered metasurface exhibits high similarity to the target electric field, which demonstrates the effectiveness of our design. Encouragingly, this work provides a monolithic field-to-pattern design method for CAHMs, which paves a new route for the direct reconstruction of metasurfaces.

On the Design of Multibeam Digital Metasurfaces With Multiple Feeds

AbstractIn this paper, an analytical design procedure for multibeam metasurfaces with multiple feeds is presented. Considering arbitrary number of input and output beams, the required amplitude and phase distributions on the metasurface plane are theoretically derived without any optimization process. How the limitation of using only passive metasurfaces poses different challenges in the practical implementation of the amplitude profile is discussed. Then, to resolve these problems, a filtering procedure is proposed which effectively produces the desired output pattern. Moreover, the design method is verified through introducing a reflective metasurface with three input beams and sixteen output beams in arbitrary directions. It utilizes a graphene‐based unit cell providing simultaneous 2/2‐bit phase/amplitude modulation, that is, totally 16 states. For validation purposes, the analytical results are compared with numerical full‐wave simulation ones in which a good agreement between them is observed. In addition, by using the proposed design method, three different practical cases for wave manipulation functionalities, including power control, beam steering, and radar cross section (RCS) reduction capabilities are demonstrated. The presented approach paves the way for efficient design of the metasurfaces for a multitude of applications, including reconfigurable intelligent surfaces and multifunctional surfaces.

Fractional saturable impurity

We examine analytically and numerically the effect of fractionality on a saturable bulk and surface impurity embedded in a one-dimensional lattice. We use a fractional Laplacian introduced previously by us, and by the use of lattice Green functions we are able to obtain the bound state energies and amplitude profiles, as a function of the fractional exponent $s$ and saturable impurity strength $\ensuremath{\chi}$ for both surface and bulk impurity. The transmission is obtained in closed form as a function of $s$ and $\ensuremath{\chi}$, showing strong deviations from the standard case, at small fractional exponent values. The self-trapping of an initially localized excitation is qualitatively similar for the bulk and surface mode, but in all cases complete confinement is obtained at $s\ensuremath{\rightarrow}0$, as shown theoretically and observed numerically.

OR19-4 A Minimal Human Physiologically Based Kinetics Model of Thyroid Hormones and Effects of Endocrine-Disrupting Chemicals

Abstract Thyroid hormones (THs) thyroxine (T4) and triiodothyronine (T3) are under homeostatic and circadian control by the hypothalamic-pituitary-thyroid axis while their free plasma concentrations are strongly buffered by three TH binding proteins (THBPs): thyroxine-binding globulin (TBG), transthyretin (TTR), and albumin (ALB). The THBPs are crucial to the even delivery of THs from the blood to tissues, but their relative contributions and spatial kinetics within tissues are unclear. Many endocrine-disrupting chemicals (EDCs) can interfere with the regulation and actions of THs, some of which are structurally similar to THs with comparable or even higher binding affinities for THBPs. It has been suspected that by disrupting the binding of THs with THBPs, EDCs may alter the plasma TH concentrations and the delivery to tissues. Given that the majority of the binding sites on THBPs are unoccupied—thus available for EDC binding—it is uncertain whether TH homeostasis can be tangibly perturbed by EDC exposure. To answer these questions, we constructed a spatial multi-compartment human physiologically based kinetic (PBK) model of TH production, distribution, and metabolism. The model contains the thyroid, liver, and rest-of-body compartments with explicit descriptions of the reversible binding kinetics between THs and THBPs in the blood. The model was parameterized and validated extensively based on literature data. Here we reported several novel findings: (1) The contribution to TH tissue delivery by each THBP is not spatially constant across a tissue: ALB always contributes more THs to the arterial side of the tissue while TBG contributes more to the venous side. (2) THBPs are essential for a uniform TH tissue delivery but are cross-compensatory in this role. (3) Contrary to the long-held assumption that ALB is the dominant contributor, TBG contributes more of the THs delivered to a tissue overall than ALB and TTR. (4) Bode plot analysis using control theory suggests that a circadian signal driving T4-to-T3 conversion in the extra-thyroidal tissue is crucial to establish the distinct phase and amplitude profiles of circulating T3 and T4 in humans. (5) Displacement of THs from THBPs by high-affinity EDCs has a negligible effect on free plasma THs even under high exposures. (6) Daily exposure to THBP-binding EDCs does not affect the circadian variations in tissue delivery of THs. The PBK model can be further elaborated in the future to make tissue-specific predictions of TH kinetics. Presentation: Monday, June 13, 2022 11:45 p.m. - 12:00 p.m.

Steerable photonic jet for super-resolution microscopy

A promising technique in optical super-resolution microscopy is the illumination of the sample by a highly localized beam, a photonic jet (also called photonic nanojet). We propose a method of computation of incident field amplitude and phase profiles that produce photonic jets at desired locations in the near field after interaction with a fixed micro-scale dielectric lens. We also describe a practical way of obtaining the incident field profiles using spatial light modulators. We expect our photonic jet design method to work for a wide range of lens shapes, and we demonstrate its application numerically using two-dimensional micro-lenses of circular and square cross-sections. We furthermore offer a theoretical analysis of the resolution of photonic jet design, predicting among other that a larger lens can produce a narrower photonic jet. Finally, we give both theoretical and numerical evidence that the waist width of the achieved designed jets is increasing linearly and slowly over a large interval of radial distances. With uniform plane wave illumination, the circular two-dimensional micro-lens produces a similar-sized jet at a fixed radial distance, while the square lens does not form a jet at all. We expect our steerable optical photonic jet probe to enable highly localized adaptive real-time measurements and drive advances in super-resolution optical microscopy and scatterometry, as well as fluorescence and Raman microscopy. Our relatively weak peak jet intensity allows application in biology and health sciences, which require high resolution imaging without damaging the sample bio-molecules.

Analytical and numerical investigation of edge waves near a vertical breakwater over a convex bottom

Vertical breakwaters are commonly built on the shore, and their existence must influence the character of nearshore dynamics. Analytical solutions based on linear-shallow water equation are derived for edge waves on a convex exponential profile which may be used to idealize the actual bottom profile with a vertical breakwater at the shoreline. The free surface elevation of the edge waves is described using the first kind of the Bessel functions of order ν. The amplitude profiles are similar to those of edge waves on a sloping beach but confined to a narrower offshore domain near the vertical breakwater. The dispersion relationship is derived from the no-flux boundary condition at the vertical breakwater. The wave number is not only related to the frequency but also the water depth at the vertical breakwater and the profile parameter. The group velocity increases rapidly to the maximum value with the increase of frequency, then decreases slowly and finally approaches the classic shallow water wave celerity of the depth at the vertical breakwater. The possible reason for this distinct behavior may be because dynamic characteristics of edge waves are highly dependent on the profile. Moreover, an extensively validated Boussinesq wave model is used to conduct numerical experiments for edge waves induced by surface bumps. The numerical results are consistent with the proposed solutions, confirming the validity of the new analytical solutions.

Adiabatic inversion in an array of spherical microcrystals under conditions of the Stark effect

A model of the process of adiabatic tracking on a system of size-quantized levels of isolated spherical quantum dots (QDs) in an electric field is proposed, which, due to the Stark effect, creates intervals between levels varied by the field. The method of perturbation theory for degenerate states is used to analyze the splitting and partial lifting of the degeneracy of levels in the lower part of the spectrum of a spherical QD. Using the pseudospin electric dipole vector model, we study the process of adiabatic inversion on a system of selected pairs of QD levels, the energy intervals between which are subject to a monotonous change by an external electric field. The course of the process of adiabatic tracking is analyzed in the case of a linear dependence of the electric field on time, at different values of the amplitude of the radiation pulse field. An asymmetry in the course of change in the amplitude profile of the inversion oscillations is revealed, which can affect the process of detecting non-stationary stimulated amplification. It is pointed out that it is possible to trace the inversion process, when the variation of the resonance detuning can be determined by the selection of the radii of the spherical QDs.

Friedlander-Keller ray expansions in electromagnetism: Monochromatic radiation from arbitrary surfaces in three dimensions

The standard approach to applying ray theory to solving Maxwell’s equations in the large wave-number limit involves seeking solutions that have (i) an oscillatory exponential with a phase term that is linear in the wave-number and (ii) has an amplitude profile expressed in terms of inverse powers of that wave-number. The Friedlander–Keller modification includes an additional power of this wave-number in the phase of the wave structure, and this additional term is crucial when analysing certain wave phenomena such as creeping and whispering gallery wave propagation. However, other wave phenomena necessitate a generalisation of this theory. The purposes of this paper are to provide a ‘generalised’ Friedlander–Keller ray ansatz for Maxwell’s equations to obtain a new set of field equations for the various phase terms and amplitude of the wave structure; these are then solved subject to boundary data conforming to wave-fronts that are either specified or general. These examples specifically require this generalisation as they are not amenable to classic ray theory.

Characterization of the topography generated by low plasticity burnishing using advanced techniques

This work investigates the surface topography of AISI 304 austenitic stainless steel after low plasticity burnishing through the evaluation of the average surface roughness (Ra), surface texture direction, areal power spectral density (APSD), scale-sensitive fractal analysis and continuous wavelet transform (CWT). The reason for adopting these approaches resides in the fact that traditional amplitude profile parameters neglect dynamic aspects of the process and geometric features of the burnished surface. The direction, periodicity and anisotropy of the surface texture were influenced by number of passes and burnishing speed and, in general, less severe plastic strain conditions tended to produce surfaces with strongly anisotropic characteristics, preferred direction of motifs, with power spectrum indicating a well-defined spatial frequency of peaks, lower fractal complexity and uniform profile distribution. The increase in surface strain severity produced surfaces with more diffuse directional characteristics, which tended to present surface isotropy, higher spatial frequency dispersion of the peaks and higher fractal complexity. Furthermore, the transition from an anisotropic to an isotropic surface can occur without changes in the average surface roughness. The continuous wavelet transforms analysis indicated a dynamic variation on the surface plastic strain when burnishing. The intermediary burnishing speed induced a strong disturbance with loss of periodicity of the roughness profile, resulting in a remarkable influence on the roughness profile in small scales. The increase in number of passes elevated the plastic strain severity, affecting the surface macrogeometric profile. The isotropic surface promoted a less severe stress concentration, reducing the tensile stresses and retarding crack nucleation, thus increasing the fatigue considerably.

Self-consistent amplitude profile of ducted VLF transmitter signal due to resonant interaction with energetic electrons in the magnetosphere

Of the various sources of whistler waves in the magnetosphere, the signals from terrestrial VLF transmitters are apparently the simplest for theoretical analysis. The role of these signals in the acceleration and pitch-angle scattering of energetic electrons in the Earth’s radiation belts has not been fully studied quantitatively, despite many decades of relevant research. The main problem in studying this issue is that to calculate the acceleration and pitch-angle scattering of particles, it is necessary to know the spatial profile of the signal amplitude. This is especially critical for phase-trapped particles, for which the energy exchange with the wave is the most significant. At the same time, the wave amplitude profile itself is determined by the interaction of the wave with resonant particles. Thus, we are dealing with a self-consistent problem, which is described by a nonlinear system of equations - a kinetic equation for the distribution function of resonant particles with a self-consistent field, and an equation for the wave field, in which the nonlinear and non-local growth rate is determined by the distribution function of resonant particles. In this paper, we develop an approach to solving this system of equations and the corresponding physical problem using the method of successive approximations.

Generation of Airy beams with transmissive cross-polarization conversion metasurfaces

This paper present a 1D finite-energy Airy beam generator at 8.0 GHz using a transmissive metasurface composed of coupling-propagation-decoupling unit cells. The phase and amplitude of the cross-polarized transmitted waves can be controlled by changing the length of the stripline and the position of loaded shorting pins, respectively. Utilizing this property to reshape the field of transmitted waves in accordance with the desired phase and amplitude profile of 1D finite-energy Airy beams. The designed metasurface is fabricated to measure the quasi-nondiffraction and self-bending properties of the generated 1D Airy beams at 8.0 GHz. In addition, the presented Airy beams generator has a very thin thickness of 0.05 (≈2 mm). The measured results were found to be in good agreement with the simulated results. Thanks to the independent control of phase, amplitude and polarization, the designed unit cell can be used in structured light, beam shaping, and holography etc.

Spatiotemporal modeling of direct acceleration with high-field terahertz pulses.

We present an improved model for electron acceleration in vacuum with high-energy THz pulses that includes spatiotemporal effects. In our calculations, we examined the acceleration with 300 GHz and 3.0 THz central frequency THz pulses with properties corresponding to common sources, and compared the Gaussian and Poisson spectral amplitudes and the associated time profiles of the electric fields. Our calculation takes into account both the longitudinal field and the spatio-spectral evolution around the focus. These aspects of the model are necessary due to the tight focusing and the duration towards a single-cycle of the THz pulses, respectively. The carrier-to-envelope phase (CEP) and the tilting angle of the coincident few- or single-cycle THz pulses must be tuned in all cases in order to optimize the acceleration scheme. We reveal additionally that electron beams with different final energies and different divergences can be generated based on simulated THz pulses having different Porras factors, describing the frequency dependence of the spatiotemporal amplitude profile, which may depend strongly on the method used to generate the single-cycle THz pulses.

Capturing the amplitude and phase profile of the vortex beam based on coherent detection

In this study, we propose a scheme to capture the amplitude and phase profile of the orbital angular momentum (OAM) beam based on coherent detection. In the scheme, the OAM beam to be measured is interfered with a local plain wave which is prepared at the receiver, and two charge-coupled devices (CCDs) are used to record the constructive and destructive interference patterns. By setting the phase of the plain wave to π/2 and π, one can extract the amplitude and phase profile of the OAM beam from the two interference patterns. We verify the feasibility of the scheme by simulation and experiments. The results show that both amplitude and phase profiles of single OAM and OAM superposition modes can be captured by using the proposed scheme, and the proposed scheme shows strong robustness even under the presence of atmospheric turbulence.

Nonreciprocity with Structured Light Using Optical Pumping in Hot Atoms

Nonreciprocal transmission of structured light has possible applications in high-capacity optical communication and high-dimensional signal processing. Here, we demonstrate the magnet-free and cavity-free optical nonreciprocity of an orbital-angular-momentum (OAM) beam using optical-pumping technology with the assistance of the Doppler effect in hot atoms. By using optical pumping to induce a direction-dependent population transfer of the ground-state atoms, we realize optical nonreciprocity for the signal laser that is carrying OAM. Interestingly, an isolation ratio close to 30 dB and maximum transmission over 0.86 can be achieved simultaneously without the use of an optical cavity. Due to the unique amplitude and helical phase profile of the structured light, our proposal may open an avenue for exploring the singularity characteristics of optical nonreciprocity using structured light.

Optical force calculation in the ray-optics regime for beams with arbitrary complex amplitude profiles

In this paper, we propose an augmented ray-optics model for computation of the optical force on spherical microscopic particles due to a beam with an arbitrary complex amplitude profile. The force calculation is based on simple analytical expressions derived considering relevant beam and lens parameters. The proposed model can provide the net optical force for a beam whose intensity or amplitude as well as phase profile in the entrance pupil of the lens can be arbitrary. Accuracy of the augmented model is demonstrated by comparing numerically with the existing model and with the experimental observations considering a focused vortex beam.

Some aspects of the plasma potential in 3D simulation of ECRIS operation

A 3D particle-in-cell plus Monte Carlo collision (PIC/MCC) code is developed for the simulation of electron cyclotron resonance ion source (ECRIS). The self-consistent interaction between the plasma and the potential field is taken into account, as well as Coulomb collisions, stepwise ionization, and charge exchange collisions between particles. In addition, a precalculation module based on a single-particle approach is introduced to speed up simulations. The stable distributions of the high-energy electrons are obtained and then sent to the subsequent simulation of ECRIS operation as the well-confined warm and hot electrons. An implicit electrostatic PIC model in this simulation self-consistently describes the evolution of the ECR plasma. The results are obtained for the plasma potential in a steady state, including the global amplitude and distribution profiles. The potential distribution of the ECR plasma is characterized by magnetic fields. These results, together with those for the charge density, are analyzed and discussed from the perspective of plasma diffusion.