Nonlinear Propagation Research Articles

Bi2Te3/Sb2Te3-graphene bidirectional heterostructures: Enhancement of optical nonlinearity and short pulse generation of solid-state laser

Bi2Te3/Sb2Te3-graphene bidirectional heterostructures: Enhancement of optical nonlinearity and short pulse generation of solid-state laser

A New Approach to Analyze Nonlinear Propagation in Arbitrary RI Fiber and Study of Dynamic Dispersion Shifting and Flattening

A New Approach to Analyze Nonlinear Propagation in Arbitrary RI Fiber and Study of Dynamic Dispersion Shifting and Flattening

A standardized approach to identify nonlinearity in fighter jet noise during ground run-ups

High-intensity military sources (explosions, gunfire, fighter jet noise. . . ) fall out of the scope of linearity-based commercial software and international standards. On top of its intrinsic complexity (high temperature supersonic jet, shocks, turbulent eddies, etc), fighter jet engine noise bears additional challenges: turbulent surrounding flow, airframe interference, directionality and tonal components typical of rotating equipment. The absence of a suitable metric to determine the boundary of the nonlinear propagation region can lead to costly mispredictions in the exposure levels for noise abatement procedures and the personnel's safety. The derivative skewness of the time domain signal used as an indicator of spectral reshaping proved effective in setting a threshold to the generation of acoustic nonlinearity for seven firearms. Its application to aircraft noise is here discussed, in order to verify the claim of persistence of nonlinear behaviour at large distances and set the foundations for a common framework contemplating the peculiarities of each military noise source. The experimental data was collected during a series of static ground run-ups of an F-16 military jet aircraft. The results from five engine regimes and two propagation paths are compared with the findings from firearms, existing literature and the solution of a nonlinear acoustic propagation solver.

Modeling of Nonlinear Sea Wave Modulation in the Presence of Ice Coverage

A model accounting for the influence of ice coverage on the propagation of surface sea waves is suggested. The model includes higher-order linear and nonlinear terms in the equation of wave motion. The asymptotic solution is obtained to account for nonlinear modulated wave propagation and attenuation. Two kinds of attenuation are revealed. The influence of the higher-order nonlinear, dispersion, and dissipative terms on the shape and velocity of the modulated nonlinear wave is studied. Despite the presence of higher-order terms in the original equation, the modulated solitary wave solution contains free parameters, which is important for the possible generation of such waves.

Dynamics of nonlinear diverse wave propagation to Improved Boussinesq model in weakly dispersive medium of shallow waters or ion acoustic waves using efficient technique

Dynamics of nonlinear diverse wave propagation to Improved Boussinesq model in weakly dispersive medium of shallow waters or ion acoustic waves using efficient technique

Sound attenuation in high mach number oscillating bubble media

We study theoretically and numerically sound attenuation in bubble-containing media when the bubbles are freely oscillating at high Mach numbers. This paper expands one of the main forms of bubble-related acoustic damping factors by extending the previous theories to higher Mach numbers, further improves the theories of nonlinear sound propagation in bubble-containing media. A nonlinear sound propagation model incorporating second-order liquid compression terms is developed, expressing the sound velocity and density in the medium as a function of the driving pressure, and taking into account the higher-order liquid compression effects on sound propagation. The correctness of the proposed model is verified by comparing with a linear model and a nonlinear model containing only low-order Mach number terms. When the bubble oscillates at a high Mach number, radiation damping, which is directly related to Mach number, becomes the main damping component affecting sound attenuation. The higher the driving amplitude, the stronger the nonlinear effect, and the greater the impact of high-order liquid compression effects on the sound attenuation, the more necessary it is to use the proposed model to calculate the sound attenuation. For high Mach numbers, varying the bubble radius and bubble number density, respectively, the difference between the proposed model and the model containing only low-order Mach number terms in capturing the pressure-dependent attenuation is calculated. Due to stronger radiation damping in smaller bubbles, the effect of compressibility becomes more important. The smaller the bubble radius, the greater the half-quality factor of the curve related to the difference in attenuation calculated by the two models, the more necessary it is to calculate the pressure-dependent attenuation using the proposed model. Here, the half-quality factor is defined as the corresponding frequency bandwidth when the curve falls from the maximum value to 22 times. Without considering the coupling effect between bubbles, the half-quality factor of the curve is not affected by the bubble number density.

Non-linear thermal radiation and entropy generation on MHD Casson and Williamson hybrid nanofluids across a curved stretching sheet with Cattaneo-Christov heat flux model

This entire study aims to prove the impacts of non-linear thermal radiation and entropy generation on Casson and Williamson hybrid nanofluids through a comparative analysis of the magnetohydrodynamic flow in a porous, curved stretching sheet with the Cattaneo-Christov heat flux model. We used hybrid nanofluid blood based on gold (Au) and Aluminium oxide (Al2O3) nanoparticles. The governing non-linear coupled Partial Differential Equation (PDE) are transformed into non-linear coupled Ordinary Differential Equations (ODE) using the Maple software solver using the Homotopy Perturbation Method. The Homotopy Perturbation Method (HPM) results are compared with the Numerical Method (NM) results, and HPM gives reliable results. The results are provided through the table and graphical representations for several parameters such as velocity, temperature, entropy production, Bejan number, Nusselt number, and skin friction respectively. The velocity profile decreases for Williamson and Casson hybrid nanofluids over a curved stretching sheet while the magnetic field parameters increase. Due to magnetic force associated with Lorentz force, which is known as resistive force, velocity decreases. The Magnetic field on the entropy generation for Casson and Williamson hybrid nanofluids. As the Magnetic field increases, the entropy generation increases for Williamson and Casson hybrid nanofluids. This problem is used in various biomedical situations, including resistive impedance to flow, arteria wall shear stress, and heating impact owing to radiation throughout the surgical process by altering the strength of the applied magnetic field.

Advances in nonlinear metasurfaces for imaging, quantum, and sensing applications

Abstract Metasurfaces, composed of artificial meta-atoms of subwavelength size, can support strong light–matter interaction based on multipolar resonances and plasmonics, hence offering the great capability of empowering nonlinear generation. Recently, owing to their ability to manipulate the amplitude and phase of the nonlinear emission in the subwavelength scale, metasurfaces have been recognized as ultra-compact, flat optical components for a vast range of applications, including nonlinear imaging, quantum light sources, and ultrasensitive sensing. This review focuses on the recent progress on nonlinear metasurfaces for those applications. The principles and advances of metasurfaces-based techniques for image generation, including image encoding, holography, and metalens, are investigated and presented. Additionally, the overview and development of spontaneous photon pair generation from metasurfaces are demonstrated and discussed, focusing on the aspects of photon pair generation rate and entanglement of photon pairs. The recent blossoming of the nonlinear metasurfaces field has triggered growing interest to explore its ability to efficiently up-convert infrared images of arbitrary objects to visible images and achieve spontaneous parametric down-conversion. This recently emerged direction holds promising potential for the next-generation technology in night-vision, quantum computing, and biosensing fields.

Damped quantum drift Zakharov-Kuznetsov equation for a dissipative inhomogeneous partially degenerate plasma with quantizing magnetic field

Damped quantum drift Zakharov-Kuznetsov (DQDZK) equation is investigated in two dimensions for a spatially inhomogeneous and dissipative plasma with adiabatic electron trapping in the presence of quantizing magnetic field and partial degeneracy. Linear and nonlinear analysis is presented in detail. For the 2D case, it is observed that the angular frequency of linear drift ion acoustic wave (DIAW) exhibits a cut-off point that gets modified by Landau quantization and partial degeneracy of the trapped electrons. It is observed that the inclusion of ion-neutral collisions leads to the formation of DQDZK equation for the system under consideration. The DQDZK is solved analytically using the hyperbolic tangent method and a decaying solitary wave solution is obtained. It is shown that the effects of quantizing magnetic field, partial degeneracy, and obliqueness significantly modify the properties of the nonlinear drift ion acoustic structures. The results presented here can be gainfully employed to understand the linear and nonlinear wave propagation in dense degenerate plasmas present in astrophysical compact objects like white dwarfs and neutron stars.

Interpretable inverse-designed cavity for on-chip nonlinear photon pair generation

Inverse design is a powerful tool in wave physics for compact, high-performance devices. To date, applications in photonics have mostly been limited to linear systems and it has rarely been investigated or demonstrated in the nonlinear regime. In addition, the “black box” nature of inverse design techniques has hindered the understanding of optimized inverse-designed structures. We propose an inverse design method with interpretable results to enhance the efficiency of on-chip photon generation rate through nonlinear processes by controlling the effective phase-matching conditions. We fabricate and characterize a compact, inverse-designed device using a silicon-on-insulator platform that allows a spontaneous four-wave mixing process to generate photon pairs at a rate of 1.1 MHz with a coincidence to accidental ratio of 162. Our design method accounts for fabrication constraints and can be used for scalable quantum light sources in large-scale communication and computing applications.

Optimal operation of lithium-ion batteries in microgrids using a semidefinite thermal model

The growing adoption of microgrids necessitates efficient management of electrical energy storage units to ensure reliable and sustainable power supply. This paper investigates a thermal management system (TMS) for maintaining the longevity of large-scale batteries. To streamline the thermal modeling of batteries, the McCormick relaxation method is employed to linearize a nonlinear and interdependent heat generation model. The thermal model of the battery follows a nonlinear behavior where the generated heat makes the battery system temperature soar, thereby affecting the thermal performance of the battery. To showcase the efficacy of the proposed approach, four distinct case scenarios are studied, highlighting the critical importance of batteries within microgrid operations. A comparative analysis is conducted between linear and nonlinear models for TMS performance. A quantitative assessment based on simulation results demonstrates the precision of the linearized model, particularly in a multitemporal optimal power flow and day-ahead scheduling of microgrids incorporating energy storage units. Controlling the battery temperature within a permissible range (from 15 °C to 40 °C) is achieved by using a heating, ventilation, and air conditioning (HVAC) system. The paper explores the economic implications of energy storage units in microgrids by extracting and comparing daily operational costs with and without battery integration. The findings reveal that the inclusion of energy storage units yields substantial economic benefits, with potential profit margins of approximately 20 % during typical working days and 60 % on weekends.

Nonlinear Acoustic Holography with Adaptive Sampling.

Accurate and efficient numerical simulation of highly nonlinear ultrasound propagation is essential for a wide range of therapeutic and physical ultrasound applications. However, due to large domain sizes and the generation of higher harmonics, such simulations are computationally challenging, particularly in three-dimensional problems with shock waves. Current numerical methods are based on computationally inefficient uniform meshes that require the highest harmonic to be resolved across the entire domain. To address this challenge, we present an adaptive numerical algorithm for computationally efficient nonlinear acoustic holography. At each propagation step, the algorithm monitors the harmonic content of the acoustic signal and adjusts its discretization parameters accordingly. This enables efficient local resolution of higher harmonics in areas of high nonlinearity while avoiding unnecessary resolution elsewhere. Furthermore, the algorithm actively adapts to the signal's nonlinearity level, eliminating the need for prior reference simulations or information about the spatial distribution of the harmonic content of the acoustic field. The proposed algorithm incorporates an upsampling process in the frequency domain to accommodate the generation of higher harmonics in forward propagation and a downsampling process when higher harmonics are decimated in backward propagation. The efficiency of the algorithm was evaluated for highly nonlinear three-dimensional problems, demonstrating a significant reduction in computational cost with a nearly 50-fold speedup over a uniform mesh implementation. Our findings enable a more rapid and efficient approach to modeling nonlinear high-intensity focused ultrasound wave propagation.

20 GHz fiber-integrated femtosecond pulse and supercontinuum generation with a resonant electro-optic frequency comb

Frequency combs with mode spacing of 10–20 GHz are critical for increasingly important applications such as astronomical spectrograph calibration, high-speed dual-comb spectroscopy, and low-noise microwave generation. While electro-optic modulators and microresonators can provide narrowband comb sources at this repetition rate, a significant remaining challenge is a means to produce pulses with sufficient peak power to initiate nonlinear supercontinuum generation spanning hundreds of terahertz (THz) as required for self-referencing. Here, we provide a simple, robust, and universal solution to this problem using off-the-shelf polarization-maintaining amplification and nonlinear fiber components. This fiber-integrated approach for nonlinear temporal compression and supercontinuum generation is demonstrated with a resonant electro-optic frequency comb at 1550 nm. We show how to readily achieve pulses shorter than 60 fs at a repetition rate of 20 GHz. The same technique can be applied to picosecond pulses at 10 GHz to demonstrate temporal compression by 9× and achieve 50 fs pulses with a peak power of 5.5 kW. These compressed pulses enable flat supercontinuum generation spanning more than 600 nm after propagation through multi-segment dispersion-tailored anomalous-dispersion highly nonlinear fibers or tantala waveguides. The same 10 GHz source can readily achieve an octave-spanning spectrum for self-referencing in dispersion-engineered silicon nitride waveguides. This simple all-fiber approach to nonlinear spectral broadening fills a critical gap for transforming any narrowband 10–20 GHz frequency comb into a broadband spectrum for a wide range of applications that benefit from the high pulse rate and require access to the individual comb modes.

Perturbation analysis of nonlinear responses caused by transverse modes in AlN FBAR based on 2D scalar wave model

This paper describes perturbation analysis of nonlinear signal generation in apodized film bulk acoustic resonators using a multi-branch LCR equivalent circuit where all necessary simulation parameters are derived by the two-dimensional (2D) scalar wave model. Nonlinear signals are evaluated by adding two voltage sources representing nonlinear strain and electric flux, and their amplitude is determined by currents in the circuit for linear analysis. Simulated second and third harmonic responses agree well with experimental ones. The magnification mechanism of spurious resonances is also discussed.

Higher-order Singular Value Decomposition Filter for Contrast Echocardiography.

Assessing the coronary circulation with contrast-enhanced echocardiography has high clinical relevance. However, it is not being routinely performed in clinical practice because the current clinical tools generally could not provide adequate image quality. The contrast agent's visibility in the myocardium is generally poor, impaired by motion and non-linear propagation artifacts. The established multi-pulse contrast schemes (MPCS) and the more experimental singular value decomposition (SVD) filter also fall short to solve these issues. Here, we propose a scheme to process AM/AMPI echoes with higher-order singular value decomposition (HOSVD) instead of conventionally summing the complementary pulses. The echoes from the complementary pulses form a separate dimension in the HOSVD algorithm. Then, removing the ranks in that dimension with dominant coherent signals coming from tissue scattering would provide the contrast detection. We performed both in vitro and in vivo experiments to assess the performance of our proposed method in comparison with the current standard methods. A flow phantom study shows that HOSVD on AM pulsing exceeds the contrast-to-background ratio (CBR) of conventional AM and an SVD filter by 10dB and 14dB, respectively. In vivo porcine heart results also demonstrate that, compared to AM, HOSVD improves CBR in open-chest acquisition (up to 19dB) and contrast ratio in closed-chest acquisition (3dB).

Using machine learning to predict dinitrogen molecule density by analyzing transient-dependent nonlinear pulse propagation in an air-filled hollow core photonic crystal fiber

Pulse propagation in air-filled hollow core photonic crystal fibers has been well investigated within the last decade to generate nonlinear phenomena such as pulse compression, frequency conversion, supercontinuum (SC) generation, among others, in a highly reliable and reproducible manner. In this work, we extend the analysis to take into account the recently evidenced pulsewidth dependency of the nonlinear refraction index of air and the effects of its molecular composition, showing that this latter plays a drastic influence on the rotational Raman response as well as the nonlinear refractive index. Our study focuses on the dispersive wave and SC generation, presenting distinct effects on the spectrum due to the pulsewidths dependency along the propagation path, evidencing different spectral broadening features depending on the initial pulsewidth. Based on these results we propose a deep learning algorithm that can predict the dinitrogen molecule particle-density of an air sample from different atmospheric conditions with a relative error lower than 3%.

Bosonization, symmetry reductions, mapping and deformation method for B-extension of Sawada–Kotera equation

An extended (2+1)-dimensional shallow water wave (SWW) model governs the evolution of nonlinear shallow water wave propagation in two spatial and a temporal coordinate. The multi-linear variable separation approach is applied to the SWW equation. The variable separation solution consisting of two arbitrary functions is given. By choosing the arbitrary functions as the exponential and trigonometric forms, some novel fission and fusion phenomena including the semifoldons, peakons, lump, dromions and periodic waves are graphically and analytically studied. The results enhance the variety of the dynamics of the nonlinear wave fields related by engineering and mathematical physics.

Unveiling Local Optical Properties Using Nanoimaging Phase Mapping in High-Index Topological Insulator Bi2Se3 Resonant Nanostructures.

Topological insulators are materials characterized by an insulating bulk and high mobility topologically protected surface states, making them promising candidates for future optoelectronic and quantum devices. Although their electronic properties have been extensively studied, their mid-infrared (MIR) properties and prospective photonic capabilities have not been fully uncovered. Here, we use a combination of far-field and near-field nanoscale imaging and spectroscopy to study chemical vapor deposition-grown Bi2Se3 nanobeams (NBs). We extract the MIR optical constants of Bi2Se3, revealing refractive index values as high as n ∼ 6.4, and demonstrate that the NBs support Mie resonances across the MIR. Local near-field reflection phase mapping reveals domains of various phase shifts, providing information on the local optical properties of the NBs. We experimentally measure up to 2π phase-shift across the resonance, in excellent agreement with finite-difference time-domain simulations. This work highlights the potential of Bi2Se3 for quantum circuitry, nonlinear generation, high-Q metaphotonics, and photodetection.

Generation Mechanisms of Hiss‐Like Chorus in the Earth's Magnetosphere

AbstractWhistler mode chorus waves appear either as a series of discrete elements (rising or falling tones) or as banded hiss‐like emissions in the dynamic spectrogram. Although the generation of rising‐tone chorus waves has been extensively studied, few studies have focused on the generation of hiss‐like emissions. In this paper, using the one‐dimensional (1‐D) general curvilinear particle‐in‐cell (gcPIC) simulation model, we have thoroughly studied the generation mechanisms of hiss‐like emissions. Based on the spectrogram, we first classify hiss‐like emissions into four types (I, II, III, and IV). We find that the type I hiss‐like waves are linearly excited by the anisotropic electrons, while other types are excited through the nonlinear process. For the type I waves, they do not undergo a frequency chirping process and have a relatively broadband spectrum. The high proportion of hot electrons or the large temperature anisotropy of hot electrons will decrease the threshold for nonlinear growth and cause the wave amplitudes to exceed the threshold, leading to the nonlinear generation of type II hiss‐like waves. The fresh hot electrons continually injected into the system with a large drift velocity significantly reduces the time interval between the rising tone elements to form a continuous spectrum, which are the type III waves. The intense and long‐lasting hiss‐like emissions, that is, type IV, which are the most frequently observed, should be generated due to the combined effect of the rapid injection and the high proportion of hot electrons (or the large temperature anisotropy). Our findings provide a comprehensive understanding of the generation of hiss‐like chorus waves in the Earth's magnetosphere.

Numerical model of nonlinear elastic bulk wave propagation in solids for non-destructive evaluation

Nonlinear ultrasonic techniques can be difficult and non-intuitive to understand due to the range of wave mixing combinations available between similar or different wave modes. To overcome this, a numerical model that uses a Finite Difference Time Domain (FDTD) scheme, without a staggered grid system, to solve the nonlinear elastic bulk wave equations in two dimensions is proposed in this paper, with the purpose of better understanding nonlinear ultrasonic techniques. Both material and geometrical nonlinearities are considered and a stress-type boundary condition is used to model the excitation. The energy transfer between frequency bands is shown and the amplitude trend of the harmonics are validated against available theories. It is then used to simulate the nonlinear ultrasonic field generated by a finite-size element of an array in a solid to better understand its behaviour. An array-element directivity at the second harmonic frequency is shown. Since the FDTD model does not account for attenuation, a correction using a ray-based approach is applied to the simulated result for direct comparison against experimental measurements. The field obtained from a typical array used in non-destructive testing is then simulated to characterise its behaviour. Experimental comparison of the nonlinear displacement fields for different focal positions showed good agreement, further validating the FDTD model. This FDTD model opens opportunities to virtually experiment and design appropriate nonlinear ultrasonic array inspections whilst isolating and understanding contribution from material nonlinearity.