Strong Nonlinear Response Research Articles

2D sheets of MoSe2 for waveguide based second harmonic generation

Two-dimensional transition metal dichalcogenides show a strong second-order nonlinear response, which can only be exploited if the interaction between light and 2D material is maximized as it happens in waveguiding structures. Such an approach also allows the addition of a second order nonlinear response to linear integrated optics components by just placing a sheet of transition metal dichalcogenides material on top. Here, we analyze the second harmonic generation in MoSe2 sheets combined with silicon nitride ridge and thin-film waveguides for both modal phase matching and quasi-phase-matching. The calculated second harmonic generation efficiency is comparable with that in lithium niobate waveguides and can further be enhanced by increasing the number of MoSe2 layers on top of the waveguides. This also holds true for flux correlated photons generated by spontaneous parametric down conversion as we show by quantitative analysis.

Analogical atomic effects of graphene nanostructure induced by nonlinearity.

A scheme to construct analogical atoms using graphene nanostructures via quantum nonlinearity is proposed. Due to the strong field localization capability of graphene plasmons and the significant intrinsic nonlinearity of graphene, a strong nonlinear optical response can be realized even with single-photon excitation. In this process, the quantum vacuum localized plasmonic mode plays a crucial role in achieving the third-order multi-photon nonlinear effect. The eigenfrequency of the nanostructure can shift by an amount tens of times larger than the decay rate, causing the nanostructure cavity to exhibit atomic-like behaviors. Furthermore, multilevel atoms can be constructed through the interaction of composite graphene nanostructures. The parameters of these atoms can be manipulated by adjusting the nanostructure size, Fermi energy, and other parameters. This research holds significant potential for applications in highly integrated, controllable nanophotonics.

Numerical study of the linear and non-linear damping in an acoustically forced cold-flow test rig with coupled cavities

Quantifying the oscillation amplitude of thermoacoustic instabilities remains a critical and challenging issue, as it is a complex balance between driving and damping processes. The New Pressurized Coupled Cavities (NPCCs) setup designed for the study of acoustic damping is analyzed in this work. It is a cold-flow test rig mimicking the geometry of a liquid rocket engine and equipped with an acoustic forcing device. The chamber 1T mode triggers a strong non-linear harmonic response, while the 1T1L and 1T2L exhibit weak non-linearities. Disturbance energy budgets are used in large-eddy simulations to characterize the damping phenomena with the 1T2L and 1T1L forcing. The correct global damping of the system is retrieved, and local damping contributions are extracted. Then, a non-linear term representing the energy transfer to the harmonics is derived from non-linear acoustics theory. Combined with a linear model, this model correctly retrieves the limit-cycle of the 1T mode.

Janus Doping of Sulfur into Platinum Diselenide Ribbons.

2D platinum diselenide (PtSe2), a novel member of the transition metal dichalcogenides (TMDCs) family, possesses many excellent properties, including a layer-dependent bandgap, high carrier mobility, and broadband response, making it promise for applications in technologies like field-effect transistors and room-temperature photodetectors. Doping represents an effective method to modify the electrical properties of 2D TMDCs and to bestow upon them additional functions. However, to date, little research has been conducted on the successful doping of 2D PtSe2 for modification. In this study, sulfur (S) powder is utilized during the chemical vapor deposition growth process of 2D PtSe2 ribbons and successfully integrated into the PtSe2 lattice through substitutional doping. The Au substrate significantly decreases the substitution energy of Se atoms in the lower layer of PtSe2, resulting in the formation of the Janus PtSSe structure. S-doped PtSe2 ribbons demonstrate significant symmetry breaking and enhanced electrical properties, showcasing a strong nonlinear optical response and certain synaptic plasticity, further simulating some neuromorphological processes. This study not only demonstrates a viable method for controllable doping and modification of 2D PtSe2 but also establishes a platform for exploring the characteristics of Janus TMDCs.

The nonlinear optical properties of meso-substituted porphyrins using spatial self-phase modulation

Herein, we studied the nonlinear optical properties of four meso-substituted porphyrins (H2MHTPP, H2THTPP, H2DETPP, and H2TETPP) by the spatial self-phase modulation (SSPM) method, using CW lasers with wavelengths of 532 nm and 780 nm. All samples exhibit strong nonlinear response due to the thermal optical nonlinear effect at 532 nm, which corresponds to the strong absorption band. In addition, four porphyrin samples were calculated that have nonlinear refractive index coefficients of the same order of magnitude (10−10 m2/W) at 532 nm. However, four porphyrins exhibited different optical nonlinear responses affected by the type and numbers of peripheral substituents at 780 nm. This work is of significance for reasonably adjusting the structure of compounds and improving their third-order nonlinear optical coefficients.

Nonlinear absorption conversion of epsilon-near-zero multilayer metamaterial at optical frequencies.

Modern all-optical logic switches demand selective, precise, and rapid transmission of optical information. In this study, we investigate an epsilon-near-zero (ENZ) metamaterial composed of silver (Ag) and magnesium fluoride (MgF2), which demonstrates a low conversion threshold, strong nonlinear response, and nonlinear absorption conversion. Particularly noteworthy is its highest nonlinear absorption (β≈-2 × 106 cm/GW) occurring at the ENZ point (695 nm) under deposited condition. This research marks the first discussion of nonlinear absorption conversion in the ENZ multilayer metamaterial. The deposited metamaterial sample exhibits saturation absorption (SA), attributed to ground state free electron bleaching, while annealed sample shows a transition from SA to reverse saturation absorption (RSA) due to a three-photon absorption effect. Annealing significantly reduces the laser power threshold required for this conversion process, indicating reduced risk of laser-induced damage. Furthermore, the wavelength shift of the largest RSA (γ≈1.93 × 104 cm3/GW2) in the annealed sample aligns with the expected redshift direction of the ENZ region (735 nm). Our metamaterial design achieves enhanced nonlinear absorption and low-power absorption conversion, which holds significant potential for applications in all-optical logic switches.

Wide-Bandgap 2D SnS2-Based All-Optical Photonic Devices with Strong Nonlinear Optical Response due to Spatial Self-Phase Modulation

Wide-Bandgap 2D SnS₂-Based All-Optical Photonic Devices with Strong Nonlinear Optical Response due to Spatial Self-Phase Modulation

Multiwalled boron nitride nanotubes with a strong nonlinear chiroptical response.

Multiwalled boron nitride nanotubes with a strong nonlinear chiroptical response.

Strong chiroptical nonlinearity in coherently stacked boron nitride nanotubes.

Nanomaterials with a large chiroptical response and high structural stability are desirable for advanced miniaturized optical and optoelectronic applications. One-dimensional (1D) nanotubes are robust crystals with inherent and continuously tunable chiral geometries. However, their chiroptical response is typically weak and hard to control, due to the diverse structures of the coaxial tubes. Here we demonstrate that as-grown multiwalled boron nitride nanotubes (BNNTs), featuring coherent-stacking structures including near monochirality, homo-handedness and unipolarity among the component tubes, exhibit a scalable nonlinear chiroptical response. This intrinsic architecture produces a strong nonlinear optical response in individual multiwalled BNNTs, enabling second-harmonic generation (SHG) with a conversion efficiency up to 0.01% and output power at the microwatt level-both excellent figures of merit in the 1D nanomaterials family. We further show that the rich chirality of the nanotubes introduces a controllable nonlinear geometric phase, producing a chirality-dependent SHG circular dichroism with values of -0.7 to +0.7. We envision that our 1D chiral platform will enable novel functions in compact nonlinear light sources and modulators.

Large‐Scale Bottom‐Up Fabricated 3D Nonlinear Photonic Crystals

Nonlinear optical effects are used to generate coherent light at wavelengths difficult to reach with lasers. Materials periodically poled or nanostructured in the nonlinear susceptibility in three spatial directions are called 3D nonlinear photonic crystals (NPhCs). They enable enhanced nonlinear optical conversion efficiencies, emission control, and simultaneous generation of nonlinear wavelengths. The chemical inertness of efficient second‐order nonlinear materials () prohibits their nanofabrication until 2018. The current methods are restricted to top‐down laser‐based techniques limiting the periodicity along the z‐axis to . The first bottom‐up fabricated 3D NPhC is demonstrated in sol–gel‐derived barium titanate by soft‐nanoimprint lithography: a woodpile with eight layers and periodicities of (‐plane) and (z‐plane). The surface areas exceed , which is two orders of magnitude larger than the state‐of‐the‐art. This study is expected to initiate bottom‐up fabrication of 3D NPhCs with a supremely strong and versatile nonlinear response.

Strongly Interacting Photons in 2D Waveguide QED.

One-dimensional confinement in waveguide quantum electrodynamics (QED) plays a crucial role to enhance light-matter interactions and to induce a strong quantum nonlinear optical response. In two or higher-dimensional settings, this response is reduced since photons can be emitted within a larger phase space, opening the question whether strong photon-photon interaction can be still achieved. In this study, we positively answer this question for the case of a 2D square array of atoms coupled to the light confined into a two-dimensional waveguide. More specifically, we demonstrate the occurrence of long-lived two-photon repulsive and bound states with genuine 2D features. Furthermore, we observe signatures of these effects also in free-space atomic arrays in the form of weakly subradiant in-band scattering resonances. Our findings provide a paradigmatic signature of the presence of strong photon-photon interactions in 2D waveguide QED.

Hydrophobin-Coated Perfluorocarbon Microbubbles with Strong Non-Linear Acoustic Response

Gas-filled microbubbles are well-established contrast agents for ultrasound imaging and widely studied as delivery systems for theranostics. Herein, we have demonstrated the promising potential of the hydrophobin HFBII—a fungal amphiphilic protein—in stabilizing microbubbles with various fluorinated core gases. A thorough screening of several experimental parameters was performed to find the optimized conditions regarding the preparation technique, type of core gas, HFBII initial concentration, and protein dissolution procedure. The best results were obtained by combining perfluorobutane (C4F10) gas with 1 mg/mL of aqueous HFBII, which afforded a total bubble concentration higher than 109 bubbles/mL, with long-term stability in solution (at least 3 h). Acoustic characterization of such microbubbles in the typical ultrasound frequency range used for diagnostic imaging showed the lower pressure resistance of HFBII microbubbles, if compared to conventional ones stabilized by phospholipid shells, but, at the same time, revealed strong non-linear behavior, with a significant harmonic response already at low acoustic pressures. These findings suggest the possibility of further improving the performance of HFBII-coated perfluorinated gas microbubbles, for instance by mixing the protein with other stabilizing agents, e.g., phospholipids, in order to tune the viscoelastic properties of the outer shell.

Effects of groundwater level decline on soil‐vegetation system in semiarid grassland influenced by coal mining

AbstractAlthough it is well known that groundwater significantly influences the plant communities, there have been few studies on how the soil and plant communities respond to a rapid decline of groundwater in a short time affected by coal mining. This paper focuses on the examination of changes in groundwater depth before and after coal mining and the soil‐vegetation response in a typical semi‐arid grassland coal mine area of Hulunbuir Steppe, Northeastern China. The IsoSource model, based on the dual stable isotopes of δ D and δ18O, was employed to estimate groundwater contributions to shallow soil (0–100 cm) water under different groundwater depths. The results revealed that groundwater was the dominant water source (75.7% ± 17.1%) for shallow soil water when the groundwater depth is less than 4 m, indicating that 4 m is a threshold in groundwater depth, separating groundwater‐dependent, and precipitation‐driven vegetation system in the study area. Secondly, a strong nonlinear response was observed between vegetation species, height, coverage, and the decline in groundwater. The vegetation properties were found to be the lowest in the areas where groundwater depth increased from 1.5–4 m to 4–28 m before and after coal mining. Finally, the groundwater level decline in the mining area significantly influenced the groundwater‐dependent vegetation ecosystem, the soil cation exchange capacity and organic matter reduced lead to the degradation of plant communities and the transition of mesophytes to xerophytes. Besides, the soil‐vegetation system in the non‐groundwater‐dependent area has no obvious response to the groundwater decline. These results suggest that caution should be exercised when mining in groundwater‐dependent ecosystem regions.

Broadband nonlinear modulation of incoherent light using a transparent optoelectronic neuron array

Nonlinear optical processing of ambient natural light is highly desired for computational imaging and sensing. Strong optical nonlinear response under weak broadband incoherent light is essential for this purpose. By merging 2D transparent phototransistors (TPTs) with liquid crystal (LC) modulators, we create an optoelectronic neuron array that allows self-amplitude modulation of spatially incoherent light, achieving a large nonlinear contrast over a broad spectrum at orders-of-magnitude lower intensity than achievable in most optical nonlinear materials. We fabricated a 10,000-pixel array of optoelectronic neurons, and experimentally demonstrated an intelligent imaging system that instantly attenuates intense glares while retaining the weaker-intensity objects captured by a cellphone camera. This intelligent glare-reduction is important for various imaging applications, including autonomous driving, machine vision, and security cameras. The rapid nonlinear processing of incoherent broadband light might also find applications in optical computing, where nonlinear activation functions for ambient light conditions are highly sought.

Nonlinear effects in manybody van der Waals interactions

Van der Waals interactions are ubiquitous and they play an important role for the stability of materials. Current understanding of this type of coupling is based on linear response theory, while optical nonlinearities are rarely considered in this context. Many materials, however, exhibit strong optical nonlinear response, which prompts further evaluation of dispersive forces beyond linear response. Here we present a approach that takes into account linear and nonlinear properties of all dipolar nanoparticles in a given system. This method is based on a Hamiltonian for nonlinear dipoles, which we apply in different systems uncovering a complex interplay of distance, anisotropy, polarizabilities, and hyperpolarizabilities in the vdW energy. This investigation broadens our basic understanding of dispersive interactions, especially in the context of nonlinear materials. Published by the American Physical Society 2024

Rational Combination of π-Conjugated and Non-π-Conjugated Groups Achieving Strong Nonlinear Optical Response, Large Optical Anisotropy, and UV Light-Switchable Fluorescence.

Combining π-conjugated and non-π-conjugated groups is an important strategy for synthesizing new nonlinear optical (NLO) crystals. However, the second harmonic generation (SHG) response and optical anisotropy can be limited by improper spatial alignment of these functional groups in the crystal structure. In this work, it is revealed that non-π-conjugated [NH2SO3] group acts as both hydrogen bond donor and acceptor, effectively regulating the 2D planar structure formed by π-conjugated [C4N3H6] groups. The resulting organic-inorganic hybrid crystal C4N3H6SO3NH2 exhibits a strong SHG response (2.5 × KDP), large optical anisotropy (0.233@546nm), and blue-violet and green fluorescence near 360 and 520nm, respectively. This work expands the methodology for creating new NLO crystals through organic-inorganic hybridization, while also showcasing the potential of C4N3H6SO3NH2 as a multifunctional optical material.

Spectral ratio analysis of the site amplification effect and nonlinear site response at MYGH10 during the 2021 MW 7.1 Fukushima earthquake in Japan

AbstractGround motion recording with peak ground acceleration (PGA) exceeding 1.43 g was observed at the Yamamoto (MYGH10) station during the MW 7.1 Fukushima earthquake off the east coast of Honshu, Japan, in February 2021. In this study, we investigated the site amplification effect and nonlinear site response at the MYGH10 site using the horizontal‐to‐vertical spectral ratio (HVSR) and surface‐to‐borehole spectral ratio (SBSR), respectively. The site transfer function of station MYGH10 was presented using HVSRs (HVSR on the ground surface) and SBSR at different frequency bands. The dominant contributing frequency band of the PGA was determined by increasing the high cutoff frequency of the bandpass filter when filtering the acceleration recording, which was used to interpret the anomaly of the PGA by combining it with the site characteristics. We found an obvious site effect below the downhole sensor through the HVSRb (HVSR on the downhole bedrock) and determined the influence of the frequency band of the downhole site on ground motion. In addition, substantial discrepancies in the frequency and amplitude between the spectral ratio curves for the Fukushima mainshock records and the weak historical motions were identified. The calculated values of the degree of nonlinearity suggested that a strong nonlinear site response occurred at station MYGH10. Finally, the recovery of the site after strong shaking was evaluated by using the average spectral ratio curves of several aftershock records.

Robust Free Excitons in CH3NH3PbI3Halide Perovskite Revealed by Four‐Wave Mixing

AbstractDirect bandgap semiconductors possess a unique attribute: the presence of a free exciton state with a high total oscillator strength. This property makes them highly promising for applications in ultrafast optical signal processing and optical computing. One such protocol for optical computing is based on four‐wave mixing (FWM). In this study, the nonlinear optical effect in polycrystalline thin films of halide perovskite MAPbI3(MA+ = CH3NH) at low temperatures is demonstrated. Through analyzing the spectroscopy of the FWM signal, studying the photoluminescence excitation spectra, and comparing the findings with results from MAPbI3single crystals, it has been discovered that the strongest nonlinear response is observed at the free exciton resonance and in the region of shallow defect states. Surprisingly, the presence of FWM in cross‐linear excitation geometry has been observed, indicating potential involvement of other nonlinear or many‐body effects. The observations of FWM with free excitons even in highly defective MAPbI3thin films demonstrate the robustness of the exciton resonance and highlight the practical prospects for utilizing this material in optical computing.

Analytical modeling of fiber–matrix interface failure in unidirectional laminae subjected to in-plane shear loads

Unidirectional laminae subjected to in-plane shear loads present complex behavior with strong nonlinear response. A novel analytical model is proposed considering a unit cell with square symmetry and circular fiber cross-section taking into account the failure on the interface between fiber and matrix. The interface failure is a shear-driven phenomenon described by a constant value during the failure process. The model validation is performed using two different approaches: the analytical estimations are compared with experimental data, and finite-element simulations are employed to evaluate the influence of fiber volume fraction. The proposed analytical model captures the main features of experimental data showing its capability and reliability to represent the complex interface debonding propagation phenomenon. Numerical simulations show in-plane shear stress–strain curves for four distinct unidirectional laminae with different fiber volume fractions. Results attest the model capability to describe composite materials with composite failure, essentially characterized by the interface behavior.

Prediction of two-dimensional 2H-M2O3 (M = Ti and Zr) with strong linear and non-linear optical response in the infrared range

Single-layer 2H-M2O3 (M = Ti and Zr) is predicted with a strong linear optical and second-harmonic generation response in the infrared range.