Nonlinear Material Research Articles

Unleashing the nonlinear optical response of layered vanadium diselenide towards the deep mid-infrared regime

Broadband nonlinear optical materials towards the deep mid-infrared regime are highly required in medical diagnostics, environmental pollution monitoring, etc. Here, we report the ultra-broadband nonlinear optical absorption behavior of the layered vanadium diselenide (VSe2) towards deep mid-infrared regime experimentally. The layered VSe2 prepared by the liquid-phase exfoliation method exhibits broadband and wavelength-dependent nonlinear saturable absorption and a large modulation depth of over 8% in the 3-10 µm spectral range. By utilizing the layered VSe2 for optical modulation, stable nanosecond pulse with a low Q-switched threshold has been delivered successfully from an erbium-doped ZBLAN fiber laser. The experimental findings can deepen the understanding of the nonlinear optical response of the transition metal dichalcogenides towards the deep mid-infrared regime, and may make inroads for the advancement of mid-IR optoelectronic devices.

Design Methods of Aluminium Pin-Ended Columns with Topology-Optimised Cross-Sections

This paper presents a numerical study of topology-optimised pin-end aluminium alloy columns using finite element analysis (FEA). The FEA models integrate geometric imperfections and material nonlinearity, and are validated against experimental findings from the existing literature. ABAQUS v.6.15 (release 2020) is used in preparing the FEA models and obtaining the analysis results. Furthermore, modern design methodologies including Eurocode 9, the direct strength method (DSM), and the continuous strength method (CSM) are employed to assess the maximum load capacity of such columns. Parametric investigations encompass diverse parameters such as varied cross-sections, column lengths, and global and local imperfections. By analysing a total of 288 FE models, incorporating 16 column cross-sections across two lengths with nine distinct imperfections, this study compares results with those derived from modern design methodologies. Thus, this research elucidates the behaviour of novel cross-sections and the application of contemporary design techniques in their analysis.

Optimization of fs-laser-induced voxels in nonlinear materials via over-correction of spherical aberration

Optimization of fs-laser-induced voxels in nonlinear materials via over-correction of spherical aberration

Investigation of column axial load effect for bolted-end-plate type steel connections

Steel moment resisting frames (MRFs) experience not only lateral movements but also vertical ones during a seismic event. Particularly, the vertical deflections in the members of the structural system cause an increase in the possibility of high column axial compressive loads (CACLs) and correspondingly the bending moment value in the beam-to-column joints. Thus, the beam-to-column joint fails in an unanticipated form. Unfortunately, the available literature about this problem is limited and inconclusive. To help bridge the gap, this study examines the effects of the CACL on the structural behavior of bolted end-plate beam-to-column connections. In this context, this study has three purposes: verifying the experimental tests by the numerical models and evaluating the CACL effect both purely and depending on the variation of fundamental parameter values governing the joint components on the verified numerical models. The numerical analyses of the reference test specimens which are borrowed from the experimental tests in the literature are conducted utilizing a finite element (FE) model including material, geometry, and contact nonlinearities. It is concluded that a possible increase in CACL causes a deterioration in the structural behavior of the beam-to-column connection depending on the moment level transferred from the connection to the column and the shear stiffness of the panel zone.

Nonlinear Dynamic Analysis Using the Force Analogy Method and the Ibarra–Medina–Krawinkler Model

ABSTRACTA methodology to integrate the Ibarra–Medina–Krawinkler (IMK) hysteretic model with the force analogy method (FAM) is proposed. FAM is a powerful tool for performing nonlinear structural analysis that reduces analysis time, addressing the main limitation of nonlinear analysis. One area of opportunity for FAM lies in its access to material nonlinearity models, which enable the reproduction of inelastic behavior in structures. The IMK model, utilized in nonlinear analysis for updating the stiffness matrix, incorporates various rules of material nonlinear behavior and considers cyclic deterioration of stiffness and strength. By combining the IMK model with FAM, the capability to model material nonlinear behavior in a computationally efficient manner is enhanced. The proposed methodology is validated through four numerical examples, demonstrating its effectiveness in replicating experimental behaviors and enhancing FAM capabilities in inelastic structural analysis.

Quantum chemical tailoring of intrinsic donor–acceptor configurations as efficient nonlinear optical materials

Quantum chemical tailoring of intrinsic donor–acceptor configurations as efficient nonlinear optical materials

Surrogate PHFGMC micromechanical models for multiscale analysis: AI-enhanced low-velocity impact analysis of hat-stiffened composite panels

The Parametric High-Fidelity Generalized Method of Cells (PHFGMC) has been established as an advanced micromechanical approach well-suited for analyzing the material nonlinearity and failure behavior of diverse periodic composite materials. In order to overcome the prohibitive computational cost of integrating micromechanical models into multiscale structural analyses as constitutive models, a proxy-surrogate modeling approach has been proposed by implementing a reduction modeling approach with deep Artificial Neural Networks (DNNs or ANNs). The PHFGMC-ANN approach has been employed to investigate the low velocity impact (LVI) analyses of hat-stiffened laminated composite panels under impact loading at various locations and energies with two different support conditions. Subsequent analysis of stiffened panels under compression loading has been conducted to understand the failure behavior of impacted panels. Further investigation was conducted into the separation between the skin and the stiffener, focusing on a single hat-stiffened coupon subjected to LVI. The analysis results have been compared against the experimental tests, and the comparison of interlaminar delamination has been used to demonstrate the efficacy of the new framework in integrating refined nonlinear micromechanical models within a multiscale analysis.

Lead‐Sulfide‐Based Hybrid Inorganic‐Organic Superlattice Particles for Prominent Nonlinear Optical Absorption

AbstractSimultaneously optimizing nonlinear absorption coefficient and modulation depth is a considerable challenge for nonlinear optical materials. Here we present an effective solution through constructing PbS2‐based inorganic‐organic superlattice. PbS2/Cn superlattice particles are synthesized, where n (4, 6, and 8) denotes the number of carbon atoms in the organic component. First‐principles simulations indicate the formation of covalent bonds and van der Waals interaction between PbS2 unit and interlayer organic molecules. All samples exhibit strong nonlinear absorption under femtosecond laser excitation with a wavelength range between 515 nm and 900 nm, and the nonlinear absorption coefficient increases with interlayer distance. The optimized sample, PbS2/C8, demonstrates outstanding nonlinear absorption and substantial modulation depth under 800 nm (the third‐order nonlinear absorption coefficient βeff, 10449 ± 609 cm GW−1; modulation depth, 39.1%) and 900 nm (the fifth‐order nonlinear absorption coefficient γeff, 6465 ± 68 cm3 GW−2; modulation depth, 88.1%), which exhibits saturable absorption under 515 nm (βeff, ‐4932 ± 818 cm GW−1; modulation depth, 48.1%). It exhibits a small optical limiting threshold of 1.23 mJ cm−2. These performances surpass those of typical single‐/few‐layer metal chalcogenides. Structural and spectral analyses elucidate that the remarkable optical nonlinearity can be attributed to quantum confinement in the inorganic layer and the dielectric enhancement of the superlattice.

Linear and nonlinear optical properties of femtosecond laser inscribed waveguides into GLS glass

Gallium lanthanum sulfide (GLS) glass is a promising material for mid-infrared photonics due to its wide transmission window and its high nonlinear refractive index that is almost three orders of magnitude higher than that of fused silica. In this paper, we present the results of a detailed study into the linear and nonlinear optical properties of waveguides fabricated in GLS glass via ultrafast laser direct-inscription using three different techniques: cumulative heating in the thermal regime as well as multi-scan and half-scan in the athermal regime. Using quadriwave lateral shearing interferometry, we fully characterized the refractive index profiles of such inscribed waveguides and found no difference between half-scan and multi-scan writing which indicates the absence of laser-induced stress in this soft glass in stark contrast to fused silica. In terms of nonlinearity, we utilized self-phase modulation (SPM)-induced spectral broadening experiments at mid-IR wavelengths to demonstrate that waveguides fabricated in the athermal regime preserve the high intrinsic nonlinearity of the GLS bulk material, outperforming those written in the thermal regime based. These findings pave the way for the fabrication of fiber-coupled optical waveguide chips for nonlinear mid-infrared photonics.

Dynamic responses of non-isolated and isolated liquid storage tanks under mainshock-aftershock sequences

After the mainshock earthquake, aftershocks often occur frequently, and the destructive effect of aftershocks on structures cannot be ignored. Based on the potential flow theory, the mechanical behavior of liquid is simulated. Considering liquid-solid coupling, material nonlinearity, and liquid sloshing, a three-dimensional numerical calculation model of liquid storage tank is established. No pulse-like and pulse-like mainshock-aftershock sequences are selected, and the seismic responses of non-isolated and isolated liquid storage tanks is compared and studied. The results show that the mainshock-aftershock sequence has a significant impact on the dynamic responses of the liquid storage tank, and the maximum increase rate reaches to 195.4 %. The effect of the mainshock-aftershock sequence on the dynamic responses of non-isolated liquid storage tanks is greater than on the dynamic response of isolated liquid storage tanks. Compared with the pulse-like mainshock-aftershock sequences, the no pulse-like mainshock-aftershock sequences generally have a greater impact on the dynamic responses of the liquid storage tanks. Overall, isolation significantly reduce the impact of mainshock-aftershock sequences on the dynamic responses of liquid storage tanks, and effectively enhance the seismic performance of liquid storage tanks under mainshock-aftershock sequences.

Optical Properties of Millimeter-Size Metal-Organic Framework Single Crystals Using THz Techniques

Metal-organic frameworks (MOFs) crystals are promising emerging materials for terahertz (THz) photonics i.e., for THz wave generation through difference frequency or optical rectification and electrooptic detection, including optical components for THz beam steering. The present work reports optical properties of three different non-centrosymmetric single MOF crystals, grown by an innovative solvo-thermal technique with tunable morphology, termed MOF [Zn(3-ptz)2]n (MIRO-101). THz time-domain spectroscopy (TTDS) in the range of 0.25 – 1.5 THz has been used for the measurement of the transfer function, H(ω) of these MOF crystals. Through this experimental function Hexp(ω), optical parameters such as refractive index, nMOF(ω) and absorption coefficient,αMOF(ω) have been calculated for the analysis of the optical properties of this crystal. The results indicate that this MOF crystal offers opportunities for long-term exploration of properties toward the creation of novel nonlinear THz photonics materials, as a THz radiation emitter via Different Frequency Generation (DFG) or Optical Rectification (OR) and Electro-optic (EO) detection via optical sampling, including for its use in optoelectronics, and materials science.

Synthesis, structural characterization and third-order nonlinear optical study of W/Cu/S cluster-based coordination polymers with thioether-containing ligands

The assembly of [Et4N][Tp*WS3] (Et = ethyl, Tp* = tetrakis(3,5-dimethyl-1-pyrazolyl)borate), Cu(I) with 1,3,5-tri((pyridin-4-ylthio)methyl)benzene (tptmb) or 4,4′-bis((pyridin-4-ylthio)methyl)-1,1′-biphenyl (bptmb) leads to two coordination polymer with the formulae of {[Tp*WS3Cu3(tptmb)(CH3CN)](PF6)2·CHCl3·2CH3CN}n (1·CHCl3·2CH3CN) and {[(Tp*WS3Cu3)2(bptmb)3(CH3CN)](PF6)4·5CH2Cl2·1.5CH3CN}n (2·5CH2Cl2·1.5CH3CN), respectively. Compounds 1 and 2 were characterized by elemental analysis, infrared spectroscopy, UV–vis spectroscopy, high-resolution electrospray ionization mass spectrometry, and single-crystal X-ray diffraction. In 1, each tptmb ligand connects two adjacent cluster nodes by its three coordination arms, forming a cluster-based one-dimensional zigzag chain. In 2, equal amounts of [Tp*WS3Cu3(CH3CN)]2+ and [Tp*WS3Cu3]2+ clusters serve as three-connected nodes and are alternatively bridged by the bptmb ligands, forming a 2D network. Z-scan tests of 1 and 2 in dimethylformamide (DMF) solution reveal they have reverse saturable absorption with effective nonlinear absorption coefficients of 1.50 × 10−11 m/W for 1 and 5.00 × 10−11 m/W for 2. This work could inspire the construction of coordination polymer structures using cluster nodes and flexible thioether-containing ligands, providing a new way for the development of third-order nonlinear optical materials.

Programable shape recovery properties and snap-through instabilities of viscoelastic and shape-memory NS metamaterials

The combination of smart material and mechanical metamaterial has the potential to bring novel properties and additional functionalities, which, however, has been ignored for a long time. This work numerically, experimentally, and analytically examines the negative stiffness (NS) metamaterials based on shape memory polymers (SMPs) with a focus on the tunable and temperature-dependent properties induced by the interaction of material and geometry nonlinearity. A universal discrete model of a series of shape-memory NS metamaterial is developed by separating the bending effect and stretching effect, where the viscoelastic material is described by the generalized Maxwell-Wiechert model, and an SMP constitutive model is proposed based on multiplicative decomposition of the deformation gradient. The mechanical and shape-memory properties influenced by temperature, geometry, material and loading rate are experimentally observed through relaxation tests and cyclic compression tests. Then the discrete model and finite element analysis (FEA) is adopted to examine the novel mechanical responses in a wide range of parameters. Results show that viscoelasticity and loading rate play a significant role in mechanical responses, and tunable load-capacity and stability can be achieved for shape-memory metamaterial. A phase diagram of different stabilities is constructed showing strictly monotonic, S-shaped, and snapping responses. Additionally, repeated compression and recovery performance proves the possibility of reusable applications. This work provides new opportunities for functional metamaterial to obtain programmable shape recovery and mechanical responses.

Various pulse nonlinear evolution and dynamics employing CuCrO2 nanocrystals as a promising saturable absorber

Considering that fiber lasers are a far richer nonlinear optical system, a systematical study on various pulse nonlinear evolution and dynamics by one SA has great significance. However, investigating these important pulse nonlinear dynamic evolution processes of CuCrO2 nanocrystals as new SAs applied in ultrafast fiber lasers has never been explored. Herein, we demonstrate the excellent nonlinear optical properties of CuCrO2 nanocrystals and investigate the potential of CuCrO2 nanocrystals for generating various pulse nonlinear dynamic evolution processes. Firstly, the output characteristics of the passively Q-switching pulsed fiber lasers have been regulated by using CuCrO2 nanocrystals-polyimide film and a tapered fiber. The pulse duration and repetition rate were simultaneously compressed by 10 and 222 times, the pulse energy and peak power were increased by 79 and 827 times, respectively. Secondly, we are able to generate chaotic multi-pulse wave packets and optical rogue waves by the polarization mode dispersion of single-mode fiber together with the non-instantaneous relaxation of CuCrO2 nanocrystals. Finally, the transition from chaotic multi-pulse wave packet to giant chirped mode-locked pulse is realized by introducing high nonlinear fibers. Our results show that CuCrO2 nanocrystals are an efficient nonlinear material for studying various nonlinear phenomena, and give a new impetus to the development of nonlinear optics and ultrafast photonics.

Measurement Technique for the Absolute Acoustic Nonlinearity Parameter Employing Only a Narrowband Pulser

In the nonlinear ultrasonic technique, the measurement of the absolute acoustic nonlinearity parameter is employed to obtain quantitative material nonlinearity. In the piezoelectric method, this measurement involves two processes: calibration and harmonic measurements. In the calibration process, a transfer function is obtained, and distortion of the propagating wave is measured in the harmonic measurement. In the conventional method for this measurement, a narrowband pulser is typically used for the harmonic measurement, while a broadband pulser is used for the calibration measurement. In this study, we propose a technique that utilizes a narrowband pulser for both harmonic and calibration measurements. First, we introduced the proposed method to measure the transfer function in the calibration measurement employing the narrowband pulser. Then, we compared the results of the transfer functions and the absolute acoustic nonlinearity parameters obtained using both a narrowband and broadband pulser in the calibration. Based on the experimental results, we found that the results obtained using both the proposed and conventional methods are highly similar, confirming the validity of the proposed measurement technique. In conclusion, even though we exclusively employ the narrowband pulser, we can accurately measure the absolute nonlinearity parameter, leading to a reduction in the required measurement equipment.

Exploiting Deep‐Ultraviolet Nonlinear Optical Material Rb2ScB3O6F2 Originated from Congruously Oriented [B3O6] Groups

AbstractThe exploration and research for deep‐ultraviolet (UV) nonlinear optical (NLO) crystals are of great significance for all‐solid‐state lasers. This work is based on the excellent structural [B3O6] units which manipulate the excellent performances of famous commercial NLO crystal β‐BaB2O4 (β‐BBO) to explore new alternatives of deep‐UV NLO materials. A deep‐UV rare‐earth metal borate fluoride Rb2ScB3O6F2 (RSBF) is successfully designed by combining the heterovalent ions substitution strategy, and fluorination strategy. Expectedly, RSBF exhibits an extremely short cutoff edge below 175 nm (189 nm for β‐BBO), and a moderate birefringence of 0.088 at 1064 nm. The shortest phase‐matching (PM) wavelength of RSBF (λPM=182 nm) is shortened by 23 nm compared with β‐BBO (λPM=205 nm) due to the improvements in the chromatic dispersion and cutoff edge, and an experimental frequency‐doubling effect 1.4×KH2PO4 (KDP) further suggests that RSBF can output a deep‐UV harmonic laser. This work provides new sights from the original influencing factors for the rational and purposeful design of deep‐UV NLO materials.

Strain-concentration for fast, compact photonic modulation and non-volatile memory

A critical figure of merit (FoM) for electro-optic (EO) modulators is the transmission change per voltage, dT/dV. Conventional approaches in wave-guided modulators maximize dT/dV via a high EO coefficient or longer light-material interaction lengths but are ultimately limited by material losses and nonlinearities. Optical and RF resonances improve dT/dV at the cost of spectral non-uniformity, especially for high-Q optical cavity resonances. Here, we introduce an EO modulator based on piezo-strain-concentration of a photonic crystal cavity to address both trade-offs: (i) it eliminates the trade-off between dT/dV and waveguide loss—i.e., enhancement of the resonance tuning efficiency dv c /dV for the fixed EO coefficient, waveguide length, and cavity Q—and (ii) at high DC strains it exhibits a non-volatile (NV) cavity tuning Δvc,NV for passive memory and programming of multiple devices into resonance despite fabrication variations. The device is fabricated on a scalable silicon nitride-on-aluminum nitride platform. We measure dv c /dV=177±1MHz/V, corresponding to Δv c =40±0.32GHz for a voltage spanning ±120V with an energy consumption of δU/Δv c =0.17nW/GHz. The modulation bandwidth is flat up to ωBW,3dB/2π=3.2±0.07MHz for broadband DC-AC and 142±17MHz for resonant operation near a 2.8 GHz mechanical resonance. Optical extinction up to 25 dB is obtained via Fano-type interference. Strain-induced beam-buckling modes are programmable under a “read-write” protocol with a continuous, repeatable tuning range of 5±0.25GHz, allowing for storage and retrieval, which we quantify with mutual information of 2.4 bits and a maximum non-volatile excursion of 8 GHz. Using a full piezo-optical finite-element-model (FEM) we identify key design principles for optimizing strain-based modulators and chart a path towards achieving performance comparable to lithium niobate-based modulators and the study of high strain physics on-chip.

Polymerization‐induced Chiral Self‐assembly for the In situ Construction, Modulation, Amplification and Applications of Asymmetric Suprastructures

AbstractIn the polymerization‐induced chiral self‐assembly (PICSA) process, chiral functional monomers undergo spontaneous supramolecular self‐assembly and asymmetric stacking during living polymerization, leading to the in situ generation of chiroptical polymer assemblies characterized by diverse morphologies. The PICSA strategy facilitates precise control and manipulation of both non‐covalent supramolecular helices and covalent macromolecular helices within aggregated cores, thereby driving significant advancements in fields such as chiral recognition materials, asymmetric catalysts, nonlinear optical materials, and ferroelectric liquid crystals (LC). This minireview summarizes recent developments in the in situ chiroptical construction and modulation associated with the PICSA methodology. Furthermore, it seeks to elucidate emerging PICSA systems founded on various living polymerization mechanisms, exploring hierarchical chirality transfer processes and the pathway complexities in both equilibrium and non‐equilibrium conditions. This minireview also presents several illustrative examples that demonstrate the practical applications of chiral polymer materials synthesized through the PICSA approach, thereby illuminating future opportunities in this innovative field.

Application of the Southwell Method to Determine the Critical Load of Compression Rods Made of Nonlinear Materials

Experimental determination of the critical force of a compression bar made of linear material does not pose major problems. The widely used Southwell method is also applicable to bars with cross-sections varying in length. The purpose of the research undertaken was to demonstrate that this method can also be successfully applied to bars made of elastic materials exhibiting nonlinear σ(ε) characteristics. Using analytical relationships for a rod satisfying the assumptions of Euler-Bernoulli theory, F(δ) relationships were derived for a rod with an initial arc imperfection, and Southwell diagrams were constructed on this basis. Nonlinear equilibrium paths F(δ) were also determined numerically using the COSMOS/M program for this purpose. For the pre-assumed different nonlinear characteristics, full confirmation of the validity of the application of the Southwell method for determining the critical force was obtained.

Ultralow-noise preamplified optical receiver using conventional single-wavelength transmission

Conventional optical amplifiers that use stimulated emission suffer from the generation of excess noise, thus limiting the performance in many applications. The phase-sensitive optical parametric amplifier, relying on the use of a nonlinear material for amplification, is an exception that can approach a noise figure of 0 dB. Its implementation in optical communication links has, however, been cumbersome due to increased complexity both in the transmitter and the receiver, effectively limiting the use of such amplifiers in practice. Here, we propose and demonstrate an implementation of a transmission system with exceptional performance in terms of receiver sensitivity (0.9 photons per bit) using a standalone ultralow-noise phase-sensitively preamplified receiver and a conventional single-wave optical transmitter. This is a significant simplification compared to previous demonstrations and can transform such amplifiers from a curiosity to practical use for example in deep-space-to-earth communication links.