Strong Nonlinear Response Research Articles

Resonant Chiral Effects in Nonlinear Dielectric Metasurfaces

We study the resonant enhancement of linear and nonlinear chiroptical effects in planar silicon metasurfaces with an in-plane asymmetry supporting multipolar Mie resonances and quasi-bound states in the continuum (quasi-BICs). We demonstrate theoretically and observe in experiment the pronounced linear circular dichroism at the quasi-BIC resonances originating from the interaction of modes with the substrate. We further find that both local field enhancement and third-harmonic signal are large for Mie resonances and some quasi-BIC modes due to the critical coupling. We demonstrate experimentally a strong nonlinear chiroptical response associated with high efficiency of the third-harmonic generation and large nonlinear circular dichroism varying from +0.918 ± 0.049 to −0.771 ± 0.004 for the samples with different asymmetries. We reveal the nonreciprocal nature of nonlinear chirality governed by the microscopic symmetry of nonlinearities and macroscopic symmetries of the meta-atom and metasurface lattice. We believe our results suggest a general strategy for engineering nonlinear chiroptical response in dielectric resonant metasurfaces.

In the quest for an optimal parametric regime of nonadiabatic switching ensuring low heat release in conjunction with high polarizability of mixed-valence molecular dimers.

The effects of electronic and vibronic interactions on the specific heat release occurring in the course of nonadiabatic switching of the electric field polarizing a one-electron mixed-valence dimer is analyzed within the framework of the Piepho-Krausz-Schatz vibronic model. The search for an optimal parametric regime from the point of view of minimizing heat release is carried out taking into account the requirement to maintain a strong nonlinear response of the dimer to the applied electric field. Calculations of the specific heat release and the response performed in the framework of the quantum mechanical vibronic approach show that although the heat release is minimal under a weak electric field acting on the dimer in combination with weak vibronic coupling and/or strong electron transfer, such a combination of the parameters is incompatible with the requirement of a strong nonlinear response. Unlike this, for molecules exhibiting strong vibronic interactions and/or weak transfer, a rather strong nonlinear response can be obtained even with a very weak electric field, which, in turn, ensures low heat release. Thus, we can conclude that an efficient strategy to improve characteristics of molecular quantum cellular automata devices or other molecular switchable devices based on mixed-valence dimers consists in usage of molecules subjected to the action of a weak polarizing field, which are characterized by strong vibronic coupling and/or weak transfer.

Strong non-linear optical response of Sb2Se3 nanorods in a liquid suspension based on spatial self-phase modulation and their all-optical photonic device applications.

The field of nonlinear optics is constantly expanding and gaining new impetus through the discovery of fresh nonlinear materials. Herein, for the first time, we have performed spatial self-phase modulation (SSPM) experiments with an emerging anisotropic Sb2Se3 layered material in a liquid suspension for an all-optical diode and all-optical switching application. The third-order broadband nonlinear optical susceptibility (χ(3)single layer ∼ 10-9 esu) and nonlinear refractive index (n2 ∼ 10-6 cm2 W-1) of Sb2Se3 have been determined using a 671 nm laser beam. This result could be unambiguously explained by the anisotropic hole mobility of Sb2Se3. The linear relationship of χ(3) and carrier mobility emphasizes the establishment of nonlocal hole coherence, the origin of the diffraction pattern. Consequently, the time evolution of diffraction rings follows the 'Wind-Chime' model. A novel photonic diode based on Sb2Se3/SnS2 has been demonstrated using the nonreciprocal propagation of light. The self-phase modulation (SPM) technique uses laser lights of different wavelengths and intensities to demonstrate the all-optical logic gates, particularly OR logic gates. The exploration of nonlinear optical phenomena in Sb2Se3 opens up a new realm for optical information processing and communication. We strongly believe that this result will help to underpin the area of optical nonlinearities among its various applications.

Ferroelectric Domain Control of Nonlinear Light Polarization in MoS2 via PbZr0.2 Ti0.8 O3 Thin Films and Free-Standing Membranes.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) such as MoS2 exhibit exceptionally strong nonlinear optical responses, while nanoscale control of the amplitude, polar orientation, and phase of the nonlinear light in TMDCs remains challenging. In this work, by interfacing monolayer MoS2 with epitaxial PbZr0.2 Ti0.8 O3 (PZT) thin films and free-standing PZT membranes, the amplitude and polarization of the second harmonic generation (SHG) signal are modulated via ferroelectric domain patterning, which demonstrates that PZT membranes can lead to in-operando programming of nonlinear light polarization. The interfacial coupling of the MoS2 polar axis with either the out-of-plane polar domains of PZT or the in-plane polarization of domain walls tailors the SHG light polarization into different patterns with distinct symmetries, which are modeled via nonlinear electromagnetic theory. This study provides a new material platform that enables reconfigurable design of light polarization at the nanoscale, paving the path for developing novel optical information processing, smart light modulators, and integrated photonic circuits.

Dichlorinated Organic‐Salt Terahertz Sources for THz Spectroscopy

AbstractAlthough in terahertz (THz) source materials molecular anions significantly influence the performance of THz generation, only limited classes of molecular counter anions have been reported. Here, utilizing dichlorinated molecular anions in THz generators is reported for the first time, to the best of our knowledge. In these new crystals, two dichlorinated molecular anions with different molecular symmetries, asymmetric 3,4‐dichlorobenzenesulfonate (34DCS) and symmetric 3,5‐dichlorobenzenesulfonate (35DCS), are incorporated with a 2‐(4‐hydroxystyryl)‐1‐methylquinolinium (OHQ) cation possessing top‐level molecular optical nonlinearity. OHQ‐34DCS exhibits a strong nonlinear optical response, in contrast to OHQ‐35DCS. In OHQ‐34DCS crystals, the dichlorinated groups form strong halogen bonds (XBs) and hydrogen bonds (HBs), which are beneficial for suppressing molecular (phonon) vibrations. The optical‐to‐THz conversion efficiency of the OHQ‐34DCS crystals is extremely high, comparable to that of the benchmark organic THz generators. Moreover, the THz emission spectra from the OHQ‐34DCS crystals, compared to those of previously reported benchmark analogous crystals, are stronger modulated toward a flatter shape, but possess substantially reduced spectral dimples. Therefore, the introduction of dichlorinated molecular anions is an efficient approach for the design of highly efficient electro‐optic salt crystals as efficient broadband THz wave sources.

Three-Dimensional Activity Volcano Plot under an External Electric Field

An external electric field (EEF) can impact a broad range of catalytic processes beyond redox systems. Computational design of catalysts under EEFs targeting specific operation conditions essentially requires accurate predictions of the response of a complex physicochemical system to collective parameters such as EEF strength/direction and temperature. Here, we develop a first-principles-based multiscale approach that enables efficient EEF-dependent kinetic modeling of heterogeneous catalysis. Taking steam reforming of methanol as an example, we find that the methanol conversion rate exhibits strong nonlinear response to temperature and EEF, and the optimal field line and constant carbon concentration line defined in the temperature--EEF parameter space serve as powerful metrics for catalyst design. Assisted with a deep neural network, we establish a three-dimensional activity volcano plot under EEFs for thousands of metallic alloys.

Influence of fault forms on the evolution of concrete damage patterns in tunnels

Quickly and accurately estimating the seismic weak surface of a fault tunnel is one of the most severe challenges in tunnel seismic design. Therefore, the strong nonlinear response of the Jinping II Hydropower Station under the dislocations of positive, reverse, and slip faults was investigated through the finite element method using a static elastoplastic model. The results reveal the damage and failure mechanism of tunnels under different faults. By using the IDA damage rating index, the damage initiation, evolution, and development process of tunnels under different types of faults are analyzed. The results showed that the affected area of fault dislocation is concentrated and intense, which is mainly distributed along the two sides of the fault surface. The damage of the positive and reverse faults to the tunnel extends from the arch waist to the vault and the invert of the arch, while the influence of the slip fault on the tunnel is the greatest at the vault and invert of the arch and then extends to the arch waist. In terms of the impact range, the reverse fault is the biggest, followed by the slip fault, while the positive fault is the lowest. This study contributes to the design and construction of tunnels through the faults.

Nonlinear decision-making with enzymatic neural networks.

Artificial neural networks have revolutionized electronic computing. Similarly, molecular networks with neuromorphic architectures may enable molecular decision-making on a level comparable to gene regulatory networks1,2. Non-enzymatic networks could in principle support neuromorphic architectures, and seminal proofs-of-principle have been reported3,4. However, leakages (that is, the unwanted release of species), as well as issues with sensitivity, speed, preparation and the lack of strong nonlinear responses, make the composition of layers delicate, and molecular classifications equivalent to a multilayer neural network remain elusive (for example, the partitioning of a concentration space into regions that cannot be linearly separated). Here we introduce DNA-encoded enzymatic neurons with tuneable weights and biases, and which are assembled in multilayer architectures to classify nonlinearly separable regions. We first leverage the sharp decision margin of a neuron to compute various majority functions on 10 bits. We then compose neurons into a two-layer network and synthetize a parametric family of rectangular functions on a microRNA input. Finally, we connect neural and logical computations into a hybrid circuit that recursively partitions a concentration plane according to a decision tree in cell-sized droplets. This computational power and extreme miniaturization open avenues to query and manage molecular systems with complex contents, such as liquid biopsies or DNA databases.

Direct Epitaxial Growth of InP Nanowires on MoS2 with Strong Nonlinear Optical Response

Mixed-dimensional van der Waals heterostructures are promising for research and technological advances in photonics and optoelectronics. Here we report vapor–liquid–solid (VLS) method-based van der Waals epitaxy of one-dimensional InP nanowires (NWs) directly on two-dimensional MoS2. With optimized growth parameters (V/III ratio, flow rates of precursors, and growth temperature), we successfully grow high-quality InP NWs on MoS2. The density and vertical yield of NWs on MoS2 are significantly high. Due to the unique properties of both materials, we observe strong linear and nonlinear optical responses from the NW/MoS2 heterostructures. Intriguingly, in addition to strong second and third harmonic responses, the mixed-dimensional heterostructures show odd-order high harmonic generation up to seventh order. Our findings can open new possibilities for advancing attosecond physics on a new platform of mixed-dimensional heterostructures.

The biogeography of relative abundance of soil fungi versus bacteria in surface topsoil

Abstract. Fungi and bacteria are the two dominant groups of soil microbial communities worldwide. By controlling the turnover of soil organic matter, these organisms directly regulate the cycling of carbon between the soil and the atmosphere. Fundamental differences in the physiology and life history of bacteria and fungi suggest that variation in the biogeography of relative abundance of soil fungi versus bacteria could drive striking differences in carbon decomposition and soil organic matter formation between different biomes. However, a lack of global and predictive information on the distribution of these organisms in terrestrial ecosystems has prevented the inclusion of relative abundance of soil fungi versus bacteria and the associated processes in global biogeochemical models. Here, we used a global-scale dataset of >3000 distinct observations of abundance of soil fungi versus bacteria in the surface topsoil (up to 15 cm) to generate the first quantitative and high-spatial-resolution (1 km2) explicit map of soil fungal proportion, defined as fungi/fungi + bacteria, across terrestrial ecosystems. We reveal striking latitudinal trends where fungal dominance increases in cold and high-latitude environments with large soil carbon stocks. There was a strong nonlinear response of fungal dominance to the environmental gradient, i.e., mean annual temperature (MAT) and net primary productivity (NPP). Fungi dominated in regions with low MAT and NPP and bacteria dominated in regions with high MAT and NPP, thus representing slow vs. fast soil energy channels, respectively, a concept with a long history in soil ecology. These high-resolution models provide the first steps towards representing the major soil microbial groups and their functional differences in global biogeochemical models to improve predictions of soil organic matter turnover under current and future climate scenarios. Raw datasets and global maps generated in this study are available at https://doi.org/10.6084/m9.figshare.19556419 (Yu, 2022).

Time series analysis of the Caspian Sea shoreline in response to sea level fluctuation using remotely sensed data

The Caspian Sea (CS), biggest inland water worldwide has experienced around 3 m oscillation in sea level during the 20th century. These rapid sea level fluctuations have had a great impact on the coastal habitat around this sea. Therefore, this study is aimed to investigate the long-term changes of the western part of the Caspian Sea shoreline and Anzali lagoon and their dynamic responses to the sea level fluctuation using time series analysis of remotely sensed data over the 40-years. To this end, the long-term Caspian Sea shoreline and the area and perimeter of the Anzali Lagoon were extracted from the time series of Landsat satellite imagery (1975 till 2016) by using an automatic procedure including the combination of the Tasseled-Cap and texture filter methods. Afterwards, shoreline erosion/accretion rates were evaluated by using the Net Shoreline Movement (NSM) and End Point Rate (EPR) techniques. Finally, the sea level changes of the CS, were extracted through the multiple altimetry satellite data and the relationship between the relative sea level fluctuation and CS shoreline and Anzali lagoon area were studied. Results of the changes of shoreline positions over the study period (1975–2016) indicate that the whole coastal study area is subjected to accretion and erosion of 20.37 and -19.22 (m/year) respectively. There is balance between the whole EPR in all transects and periods between 1975 and 2016. This shows that when erosion happens in a region, accretion will be happened in another region, and this behavior is symmetrical. When the sea level decreased, the EPR values showed the accretion/seaward and vice versa. So, the shoreline movement has a strong nonlinear response to the sea level fluctuation with a coefficient of determination of −0.66. Also results show the strong response of the Anzali lagoon to the sea level fluctuation with a coefficient of determination of 0.78 for a nonlinear relationship between the changes of area of Anzali Lagoon and the CS fluctuation. This lagoon experienced the greatest and lowest values of its area on 2003 and 1985, respectively, which are matched with the high and low stands of the Caspian Sea Level.

Optomechanical response of a strongly interacting Fermi gas

We study a Fermi gas with strong, tunable interactions dispersively coupled to a high-finesse cavity. Upon probing the system along the cavity axis, we observe a strong optomechanical Kerr nonlinearity originating from the density response of the gas to the intracavity field and measure it as a function of interaction strength. We find that the zero-frequency density response function of the Fermi gas increases by a factor of two from the Bardeen-Cooper-Schrieffer to the Bose-Einstein condensate regime. The results are in quantitative agreement with a theory based on operator-product expansion, expressing the density response in terms of universal functions of the interactions, the contact and the internal energy of the gas. This provides an example of a driven-dissipative, strongly correlated system with a strong nonlinear response, opening up perspectives for the sensing of weak perturbations or inducing long-range interactions in Fermi gases.

A Hybrid Antiperovskite with Strong Linear and Second‐Order Nonlinear Optical Responses

Antiperovskites have been studied since the 1980s because of their rich physical and chemical properties, but their linear and second-order nonlinear optical responses remain largely unknown. Here we report a new polar crystal, Cs3Cl(HC3N3S3) (I), which features a quasi-one-dimensional antiperovskite structure composed of ClCs6 polyhedra and A-site [HC3N3S3]2- rings. To our best knowledge, this kind of antiperovskite structure is reported for the first time. Remarkably, I exhibits a very strong nonlinear optical response up to 11.4 times that of the benchmark KH2PO4 and an exceptionally large birefringence of 0.52. The first-principles calculations and structural analyses reveal that [HC3N3S3]2- is the “material gene” while the antiperovskite structural feature makes it in a favorable arrangement. This work provides a new structural platform for the rational design of integrated optoelectronic materials with linear and second-order nonlinear optical responses.

A Hybrid Antiperovskite with Strong Linear and Second-Order Nonlinear Optical Responses.

Antiperovskites have been studied since the 1980s because of their rich physical and chemical properties, but their linear and second-order nonlinear optical responses remain largely unknown. Here we report a new polar crystal, Cs3 Cl(HC3 N3 S3 ) (I), which features a quasi-one-dimensional antiperovskite structure composed of ClCs6 polyhedra and A-site [HC3 N3 S3 ]2- rings. To our best knowledge, this kind of antiperovskite structure is reported for the first time. Remarkably, I exhibits a very strong nonlinear optical response up to 11.4 times that of the benchmark KH2 PO4 and exceptionally large birefringence of 0.52. The first-principles calculations and structural analyses reveal that [HC3 N3 S3 ]2- is the "material gene" while the antiperovskite structural feature making it in a favorable arrangement. This work provides a new structural platform for the rational design of integrated optoelectronic materials with linear and second-order nonlinear optical responses.

Birefringent strands drive the flow of viscoelastic fluids past obstacles

The flow of polymer solutions past solid obstacles or through porous media gives rise to rich physical phenomena over a wide range of spatial and temporal scales. Viscoelasticity, in particular, can induce a strong nonlinear response with an increase of flow resistance even for a solution whose viscosity decreases in simple shear flow. Various hypotheses have been proposed to explain this phenomenon but a clear picture of the pore-scale mechanisms involved and their impact upon larger scales is still lacking. Here, we show that localized zones of large polymeric stress, known as birefringent strands, drive the flow of an Oldroyd-B fluid through two-dimensional arrays of cylinders. Combining a recently developed numerical scheme with high performance computing, we find that these strands generate a complete reorganization of the flow with an increase of stagnation zones, a reinforcement of preferential paths and a splitting of flow channels. Furthermore, we show that this reorganization is the source of an increase in the viscous dissipation of the solvent and also that the stretching of polymer molecules in the strands is associated with entropy production. Both these phenomena yield a global increase in dissipation that can be directly linked to the increase of flow resistance. Our results demonstrate that the birefringent strands – not the elongational viscosity – drive the flow of viscoelastic fluids through porous media and that the increase of flow resistance can occur even at steady state, before the transition to elastic turbulence.

High‐frequency decay of Fourier spectra of strong motion acceleration and nonlinear site response

AbstractWe examine how the decay of high‐frequency amplitudes of Fourier spectra of strong earthquake ground acceleration (described in seismological literature by the slope parameter ) depends on the soil and geological site conditions at the recording stations in the Los Angeles metropolitan area. Then, we introduce a Gedanken numerical experiment, in which we analyze nonlinear wave motion in shallow soil and show that it also leads to similar decay of the high‐frequency spectral amplitudes. The results of both of our studies are consistent with the interpretation that the decay of high‐frequency Fourier spectra of strong motion acceleration, described by , occurs at the recording site near the ground surface.

Plasmonically enhanced two-photon absorption induced photoacoustic microscopy with laser-synthesized TiN nanoparticles

Combining photonic excitation and acoustic detection, photoacoustic imaging (PAI) presents one of the most promising noninvasive biomedical diagnostic modalities, but this technique still lacks efficient nano-sized contrast agents absorbing light in the region of relative tissue transparency (630–900 nm). Here, we explore the use of titanium nitride (TiN) nanoparticles (NPs) fabricated by methods of pulsed laser ablation in liquids as a contrast agent in PAI. When prepared in acetone, the NPs are spherical, have an average size of 25 nm, and exhibit a broad plasmonic absorption peak around 700 nm. We show that solutions of these NPs render possible a strong nonlinear photoacoustic response and the generation of photoacoustic images with 67 μm resolution within the biological transparency window. The observed effect is explained by a plasmonically enhanced two-photon absorption process in TiN NPs. Combined with earlier demonstrated capability of generating photothermal therapeutic effect, relative chemical purity, and excellent biocompatibility, laser-synthesized TiN NPs promise attractive applications in biomedical theranostics involving imaging modalities based on photoacoustics microscopy or tomography.

High kinetic inductance NbTiN superconducting transmission line resonators in the very thin film limit

We examine the DC and radio frequency (RF) response of superconducting transmission line resonators comprised of very thin NbTiN films, <12 nm in thickness, in the high-temperature limit, where the photon energy is less than the thermal energy. The resonant frequencies of these superconducting resonators show a significant nonlinear response as a function of RF input power, which can approach a frequency shift of Δf=−0.15% in a −20 dB span in the thinnest film. The strong nonlinear response allows these very thin film resonators to serve as high kinetic inductance parametric amplifiers.

Nonlinear Coherent Light–Matter Interaction in 2D MoSe2 Nanoflakes for All‐Optical Switching and Logic Applications

AbstractA strong nonlinear optical response of 2D MoSe2 nanoflakes (NFs) through spatial self‐phase modulation (SSPM) and cross‐phase modulation (XPM) induced by nonlocal coherent light–matter interactions is reported. The coherent interaction of light and MoSe2 NFs creates the SSPM of laser beams, forming concentric diffraction rings. The nonlinear refractive index (n2) and third‐order broadband nonlinear optical susceptibility (χ(3)) of MoSe2 NFs are determined from the self‐diffraction pattern at different exciting wavelengths of 405, 532, and 671 nm with varying laser intensity. The evolution and deformation of diffraction ring patterns are observed and analyzed by the “wind‐chime” model and thermal effect. By taking advantage of the reverse saturated absorption of 2D SnS2 NFs compared to MoSe2, an all‐optical diode has been designed with MoSe2/SnS2 hybrid structure to demonstrate the nonreciprocal light propagation. Few other optical devices based on MoSe2 and semiconducting materials such as Bi2Se3, CuPc, and graphene have been investigated. The all‐optical logic gates and all‐optical information conversion have been demonstrated through the XPM technique using two laser beams. The proposed optical scheme based on MoSe2 NFs has been demonstrated as a potential candidate for all‐optical nonlinear photonic devices such as all‐optical diodes and all‐optical switches.

Nonlinear Optical and Photocurrent Responses in Janus MoSSe Monolayer and MoS2-MoSSe van der Waals Heterostructure.

Two-dimensional (2D) transition metal dichalcogenides are promising materials platforms for a variety of optoelectronic device applications. Janus 2D materials are a rising class of 2D materials with low symmetry, which leads to the emergence of out-of-plane electric polarization and piezoelectricity. Using first-principles density functional theory, we show that monolayer and bilayer heterostructure Janus MoSSe moieties exhibit strong nonlinear optical responses that are vanishing in the non-Janus form. The absence of horizontal mirror plane symmetry enables a circular photocurrent as well as a large out-of-plane second harmonic generation (SHG) and shift photocurrent. Through a comparative study of the Janus heterostructure MoS2-MoSSe on five distinct stacking configurations, we find that the magnitude of the out-of-plane SHG in the Janus heterostructure is enhanced due to the interlayer coupling and interference effect compared to that of monolayer MoSSe. Thus, Janus 2D materials offer a unique opportunity for exploring nonlinear optical phenomena and designing configurable layered nonlinear optical materials.