Strong Nonlinear Response Research Articles

Strong light-matter interaction and non-linear effects in organic semiconducting CuPc nanotubes: realization of all-optical diode and switching applications.

Spatial self-phase modulation based on the optical Kerr effect has gained momentum in recent years to analyse the nonlinear optical properties of 2D inorganic nanomaterials. In the present work, we investigate the strong light-matter interaction of organic semiconducting materials based on SSPM, by developing Cu-phthalocyanine (CuPc) nanotubes via a solvothermal technique. The low bandgap of CuPc facilitates the study of its nonlinear optical properties for a broad spectrum range from 671 nm to 405 nm. Intense laser light passing through the CuPc dispersion produces concentric diffraction ring patterns at the far field from which high n2 and χ(3) values, 3.667 × 10-5 cm2 W-1 and 2 × 10-3 esu, respectively, are obtained for the 405 nm laser. This strong nonlinear optical response of CuPc has been utilized to realize non-reciprocal light propagation by constructing a CuPc/SnS2 hybrid structure, which makes an effective all-optical photonic diode. In addition, the all-optical switching is presented using CuPc nanotubes based on the spatial cross-phase modulation technique. In this technique a phase change is induced in the weak signal beam modulated by the strong controlling light beam, which helps to produce all-optical logic gates and all-optical switching devices. The experimental findings of this work unravel the potentially powerful applications of CuPc nanotubes in all-optical information transmission and all-optical photonic devices.

Mixed-Valence Bridged Norbornylogous Compounds as Switchable Cells for Molecular Quantum Cellular Automata: A Compromise between High Polarizability and Low Power Dissipation.

In this article, we analyze power dissipation in the nonadiabatic switching event in mixed-valence (MV) molecular cells of quantum cellular automata (QCA) in combination with a key functional property of cells such as polarizability in the applied electric field. We demonstrate that although the requirements for a strong nonlinear response of the cell to the applied electric field and low heat release are competing from the point of view of molecular parameters, this by no means can be regarded as an insurmountable obstacle for achieving functional advantages and possibility of practical application of QCA. The general theoretical consideration is applied to the series of MV compounds exemplifying electric field-switchable MV molecules, which include oxidized norbornadiene [C7H8]+ (I) and its polycyclic derivatives [C12H12]+ (II), [C17H16]+, (III), [C27H24]+ (IV), and [C32H28]+ (V). Based on the results of high-level ab initio calculations performed for the series of compounds with variable length of the bridge connecting redox groups, we show that strongly localized cation radicals with long bridges can be easily polarized even by a fairly weak electric field. This ensures quite low power dissipation, which is shown to coexist with a rather strong nonlinear cell-cell response. We thus conclude that consideration of the series of MV dimers with controllable electron transfer provides a reasonable way to design molecule-based QCA cells with the required properties.

Directly seeding epitaxial growth of tungsten oxides/tungsten diselenide mixed-dimensional heterostructures with excellent optical properties

Mixed-dimensional heterostructures have drawn significant attention due to their intriguing physical properties and potential applications in electronic and optoelectronic nanodevices. However, limited by the lattice matching, the preparation of heterostructures is experimentally difficult and the underlying growth mechanism has not been well established. Here, we report a three-step seeding epitaxial growth strategy for synthesizing mixed-dimensional heterostructures of one-dimensional microwire (MW) and two-dimensional atomic thin film. Our growth strategy has successfully realized direct epitaxial growth of WSe2 film on WOx MW and significantly improves the quality of the epitaxial WSe2 monolayer, which is evidenced by the remarkably enhanced photoluminescence (PL). More intriguingly, the as-synthesized WOx MWs exhibit a strong nonlinear optical response due to the enhancement effect of the core (WOx)-shell (WSe2) nanocavity. Our work provides a feasible route for direct growth of WOx-based mixed-dimensional heterostructures, which possess potential applications in high-performance optoelectronic devices.

Berry Curvature Dipole Induced Giant Mid-Infrared Second-Harmonic Generation in 2D Weyl Semiconductor.

Due to its inversion-broken triple helix structure and the nature of Weyl semiconductor, 2D Tellurene (2D Te) is promising to possess a strong nonlinear optical response in the infrared region, which is rarely reported in 2D materials. Here, a giant nonlinear infrared response induced by large Berry curvature dipole (BCD) is demonstrated in the Weyl semiconductor 2D Te. Ultrahigh second-harmonic generation response is acquired from 2D Te with a large second-order nonlinear optical susceptibility (χ(2) ), which is up to 23.3 times higher than that of monolayer MoS2 in the range of 700-1500nm. Notably, distinct from other 2D nonlinear semiconductors, χ(2) of 2D Te increases extraordinarily with increasing wavelength and reaches up to 5.58nmV-1 at ≈2300nm, which is the best infrared performance among the reported 2D nonlinear materials. Large χ(2) of 2D Te also enables the high-intensity sum-frequency generation with an ultralow continuous-wave (CW) pump power. Theoretical calculations reveal that the exceptional performance is attributed to the presence of large BCD located at the Weyl points of 2D Te. These results unravel a new linkage between Weyl semiconductor and strong optical nonlinear responses, rendering 2D Te a competitive candidate for highly efficient nonlinear 2D semiconductors in the infrared region.

Simultaneous 3D Construction and Imaging of Plant Cells Using Plasmonic Nanoprobe-Assisted Multimodal Nonlinear Optical Microscopy.

Nonlinear optical (NLO) imaging has emerged as a promising plant cell imaging technique due to its large optical penetration, inherent 3D spatial resolution, and reduced photodamage; exogenous nanoprobes are usually needed for nonsignal target cell analysis. Here, we report in vivo, simultaneous 3D labeling and imaging of potato cell structures using plasmonic nanoprobe-assisted multimodal NLO microscopy. Experimental results show that the complete cell structure can be imaged via the combination of second-harmonic generation (SHG) and two-photon luminescence (TPL) when noble metal silver or gold ions are added. In contrast, without the noble metal ion solution, no NLO signals from the cell wall were acquired. The mechanism can be attributed to noble metal nanoprobes with strong nonlinear optical responses formed along the cell walls via a femtosecond laser scan. During the SHG-TPL imaging process, noble metal ions that crossed the cell wall were rapidly reduced to plasmonic nanoparticles with the fs laser and selectively anchored onto both sides of the cell wall, thereby leading to simultaneous 3D labeling and imaging of the potato cells. Compared with the traditional labeling technique that needs in vitro nanoprobe fabrication and cell labeling, our approach allows for one-step, in vivo labeling of plant cells, thus providing a rapid, cost-effective method for cellular structure construction and imaging.

Towards Double Resonant Cavity Enhanced Second Harmonic Generation in Monolayer MoS2

AbstractA characteristic property of monolayered transition metal dichalcogenides is their strong nonlinear response. While they display a high conversion efficiency per atomic layer, due to their low thickness, the absolute value of their nonlinear response remains low. Here enhancement of the second harmonic generation (SHG) of monolayer MoS2 through the design, fabrication, and characterization of a monolithic microcavity, which aims to be double resonant at a fundamental wavelength of λ = 800 nm as well as its second harmonic, is demonstrated. The MoS2 monolayers are embedded in such a cavity, with the aim to simultaneously enhance the light‐matter interaction at the excitation wavelength and the SHG from the monolayers. A resonance enhancement for the SHG process is achieved through the cavity.

Glancing angle deposition of helical manganese oxide nanostructures on the glass substrate and study the optical nonlinearity by Z-scan technique

Helical manganese oxide nanostructures have been deposited on glass substrate by glancing angle deposition along with electron-beam evaporation technique. X-ray diffraction analysis, FESEM images, and FTIR spectroscopy confirmed the successful growth of the nanostructured thin film. The surface morphology and roughness of the deposited helical manganese oxide thin film were considered using the 2-D and 3-D AFM images. The optical constants along axes a, b, and c have been calculated from the effective medium approximation of Bruggeman. The refractive indices were found to be equal for helical manganese oxide nanostructures along a- and b-axes and greater than the refractive index along c-axis at λ < 600 nm; while these results are reversed for wavelengths greater than 600 nm. The same variations were observed for the extinction coefficients. The Z-scan measurements under continuous-wave (CW) laser irradiation at 532 nm showed a positive sign for both the nonlinear absorption coefficient and nonlinear refractive index of nanostructured helical manganese oxide demonstrating the attendance of induced absorption process and self-defocusing phenomena, respectively. We computed a 3rd-order nonlinear optical susceptibility, χ(3), equal to 0.042 esu that suggests the glancing angle deposited helical manganese oxide nanostructures with a strong nonlinear optical response can be a good candidate to develop nanophotonic devices.

Graphdiyne-Based All-Solid-State Passively Q-Switched Tm:YAP Laser at 2 μm.

All-solid-state Tm lasers have a wider wavelength range and higher output power compared to other types of lasers. In this work, we demonstrate an all-solid-state, high repetition, Tm:YAP laser Q-switched by a graphdiyne (GDY) saturable absorber. The high-quality optical nonlinear material GDY, synthesized by a cross-coupling method, exhibits a strong nonlinear optical response. The application of GDY as a saturable absorber in the passively Q-switched (PQS) Tm:YAP of an all-solid-state laser has been realized with the shortest pulse duration of ~785 ns and repetition frequency of ~199.6 kHz at a central wavelength of 1985.8 nm. This represents the shortest pulse duration and the highest repetition frequency achieved from GDY in a solid-state Tm laser to date. Our work demonstrates the remarkable nonlinear optical properties of GDY, which holds promising potential in the field of optoelectronics.

Alongwind and crosswind response of friction-pendulum base-isolated high-rise buildings

Base isolation technology is widely accepted as an effective strategy for the seismic design of buildings. Although the elastomeric isolator is still extensively adopted for the base-isolation system in practice, there is a trend to use the frictional pendulum bearing (FPB) due to its high vertical bearing capacity, stable performance and good recentering capability. In this paper, the dynamic response of base-isolated high-rise buildings with FPB having a velocity-dependent friction coefficient subjected to uncoupled alongwind and crosswind loads is studied. The response characteristics calculated from response history analysis (RHA) are analyzed. Meanwhile, two statistical linearization methods are utilized to estimate the standard deviation (STD) of the structural response and to obtain the equivalent parameters of the linearized system. The time-varying mean of the base displacement under alongwind load with a non-zero mean is also discussed by the linearization method. Finally, a parameter analysis of the isolation bearing is performed to investigate the effects of the radius and friction coefficient of the sliding plate on the wind-induced vibration. This study highlights the strong nonlinear response characteristics of base-isolated high-rise buildings with FPB and offers design guidelines under strong winds.

Rheological state variables: A framework for viscosity parametrization in crystal-rich magmas

Igneous processes involve multiphase magmas, and the rate at which these processes operate is tightly controlled by multiphase rheology. The rheology of magmatic suspensions containing irregular-shaped crystals is complex, and this complexity is illustrated by the strong non-linear response to deformation and the lack of apparent self-similarity when comparing the results of experiments conducted under different shear conditions. Structural and empirical models have been developed to describe the experimental data. However, they are not predictive due to presence of several tuning parameters and their strong dependence on the flow variables and suspension characteristics. The current study proposes a state variable framework that restores self-similarity in the rheology of crystal-rich magmas. This framework only uses two rheological state variables and defines a universal rheological model to explain the relative viscosity of magmatic suspensions while considering microstructural changes such as crystals’ orientation, deformation, and comminution as well as shear-induced heterogeneities. We show that the viscosity of crystal-rich magmas as function of crystal content obeys the well-known monotonic and divergent behavior documented for suspensions of solid particles. This is achieved when the appropriate state of crystal dispersion is obtained using a unique product of the two rheological state variables. This theoretical approach, compared to empirical models, is as powerful for fitting, and can be also extrapolated beyond experimental data used in the fitting procedure. Hence, the state variable framework can be generalized to form a unified law with predictive power. At low shear rates, this framework is fully predictive as we can directly constrain both variables and their unique product. At high shear rates, one of the variables must be computed and measured independently. It is also shown that the proposed model can be used to detect the presence of anomalies, e.g., crystal breakage and shear-induced heterogeneities, in experimental data.

Strong Nonlinear Response in Crystalline Quartz at THz Frequencies

AbstractThis study reports on the experimental observation of a very strong nonlinear response in crystalline quartz in the terahertz (THz) frequency region through THz time‐domain spectroscopy (THz‐TDS). A previously established theoretical model is modified and presented and predicts a Kerr coefficient n2 equal to 5.17 × 10−14 m2 W−1. The time‐domain analysis of the measured data shows that with increasing of the THz peak amplitude, the pulse experiences a larger time delay in the sample. As the THz amplitude increases to values higher than 110 kV cm−1, the growth rate of the delay decreases, indicating a saturation process. The value of the nonlinear refractive index calculated through the frequency‐response analysis is estimated to be on the order of 10−13 m2 W−1, which is several orders of magnitude larger than typical values of the nonlinear refractive index of solids in the visible region. Furthermore, a negative fifth‐order susceptibility on the order of 10−30 m4 V−4 is measured.

Nonlinear generation of hollow beams in tunable plasmonic nanosuspensions

We experimentally demonstrate that a probe beam at one wavelength, although exhibiting a weak nonlinear response on its own, can be modulated and controlled by a pump beam at another wavelength in plasmonic nanosuspensions, leading to ring-shaped pattern generation. In particular, we show that the probe and pump wavelengths can be interchanged, but the hollow beam patterns appear only in the probe beam, thanks to the gold nanosuspensions that exhibit a strong nonlinear response to pump beam illumination at the plasmonic resonant frequencies. Colloidal suspensions consisting of either gold nanospheres or gold nanorods are employed as nonlinear media, which give rise to refractive index changes and cross-phase modulation between the two beams. We perform a series of experiments to examine the dynamics of hollow beam generation at a fixed probe power as the pump power is varied and find that nonlinear beam shaping has a different power threshold in different nanosuspensions. Our results will enhance the understanding of nonlinear light–matter interactions in plasmonic nanosuspensions, which may be useful for applications in controlling light by light and in optical limiting.

Satellite observed response of fire dynamics to vegetation water content and weather conditions in Southeast Asia

Fires greatly affect terrestrial ecosystems, climate, human health, and economy. Under the threat of global warming, assessing fire occurrence frequency and fire danger is critical to mitigate fire’s negative impacts. The state-of-the-art satellite microwave observation provides the unique opportunity to monitor vegetation water content (VWC) for multiple vegetation strata, yet still lacks associated investigation in fire dynamics. Here, we applied the multiple microwave Emissivity Difference Vegetation Indexes (EDVIs) as VWC proxies of different vegetation strata to explore their influence on fire occurrence frequency (given by the number of fires, NOF) and the cumulative fire radiant energy (FRE) in mainland Southeast Asia during 2015–2019; and compared to that with the commonly used fire weather indices from the Canadian Forest Fire Weather Index system. Then, we identified the optimal regression models to depict the relationship of fires with EDVIs and fire weather indices, respectively; and incorporated both kinds of indices in models to retrospectively predict NOF and FRE. Results show that: (1) the monthly mean NOF and FRE nonlinearly decrease with EDVI in mainland Southeast Asia, and 40–60% of the variances are explained by EDVI, which further improve to 60–70% by incorporating EDVIs of two different vegetation layers. (2) In comparison, NOF and FRE nonlinearly increase with fire weather indices, and connections are stronger than that with EDVI; nevertheless, combing fire weather indices with EDVI, especially with EDVIs of two vegetation layers provides almost the highest explanation for fires. (3) The log-linear and/or log-quadratic models are identified to outperform the other models in depicting the fire-EDVI and fire-fire weather indices relationships; and incorporating EDVI and fire weather indices in models generally improves the prediction accuracy. These findings reveal the differentiated VWC effects on NOF and FRE among vegetation strata and quantify the strong nonlinear response of fires to VWC and weather conditions in mainland Southeast Asia, which could provide new insight for fire prediction and fire danger assessments with the utility of microwave observations.

Low-loss skimming waveguides with controllable mode leakage for on-chip saturable absorbers

Abstract Emerging 3D photonic circuits would greatly benefit from the ability to integrate skimming waveguides with low loss and controllable inscription depth into photonic circuits. These waveguides allow for the interaction of guiding light directly with external modulation signals and enable programmable photonic circuits. Here, we report the fabrication of a novel photonic-lattice-like skimming waveguide (PLLSW) using femtosecond laser writing. Our method enables fine control of cross-sectional symmetry and writing depth of waveguides, achieving a minimum depth of 1 μm and a low insertion loss of 1 dB. Based on the PLLSW, we demonstrate on-chip light modulation by designing an evanescent-field-type saturable absorber through the coupling of a carbon nanotube film with the PLLSW, which exhibits saturation intensity from 20 to 200 MW/cm2 through the balanced twin-detector measurement. The strong nonlinear optical response of the PLLSW-based saturable absorber is further exploited to drive a Q-switched pulse laser at 1550 nm based on a fiber laser cavity. Our work demonstrates an effective method to integrate nonlinear optical materials into a glass chip for all-optical switching based on 3D waveguides, which holds great potential for the construction of large-scale programmable photonic circuits in the future.

Q-switched fiber laser operating at 1560 nm modulated by Cr3C2 film

Chromium carbide (Cr3C2), as a kind of transition metal carbides, has exhibited extraordinary optoelectronic properties and aroused enormous attention. However, few reports have been focused on the nonlinear properties and relevant devices. In this study, we first demonstrated a novel Cr3C2 saturable absorber (SA). Cr3C2 with an average size of 200 nm was prepared through a low temperature salt flux synthetic method. The Cr3C2-film SA exhibited high robustness and strong linear and nonlinear saturable absorption response at 1560 nm. As the Cr3C2 SA was inserted into the Er3+-doped fiber laser cavity, Q-switched pulses were generated with a central wavelength of 1560 nm. To the best of our knowledge, this was the first report on the optical nonlinearity of Cr3C2 as a Q-switcher for the near-infrared fiber laser. Our experimental results verified that the integrated Cr3C2-based device possessed great potential as a nonlinear optical medium for high-performance optical applications.

Laser-Activated Second Harmonic Generation in Flexible Membrane with Si Nanowires.

Nonlinear silicon photonics has a high compatibility with CMOS technology and therefore is particularly attractive for various purposes and applications. Second harmonic generation (SHG) in silicon nanowires (NWs) is widely studied for its high sensitivity to structural changes, low-cost fabrication, and efficient tunability of photonic properties. In this study, we report a fabrication and SHG study of Si nanowire/siloxane flexible membranes. The proposed highly transparent flexible membranes revealed a strong nonlinear response, which was enhanced via activation by an infrared laser beam. The vertical arrays of several nanometer-thin Si NWs effectively generate the SH signal after being exposed to femtosecond infrared laser irradiation in the spectral range of 800-1020 nm. The stable enhancement of SHG induced by laser exposure can be attributed to the functional modifications of the Si NW surface, which can be used for the development of efficient nonlinear platforms based on silicon. This study delivers a valuable contribution to the advancement of optical devices based on silicon and presents novel design and fabrication methods for infrared converters.

Efficient modeling of sharp-edge acoustofluidics

Sharp-edge structures exposed to acoustic fields are known to produce a strong non-linear response, mainly in the form of acoustic streaming and acoustic radiation force. The two phenomena are useful for various processes at the microscale, such as fluid mixing, pumping, or trapping of microparticles and biological cells. Numerical simulations are essential in order to improve the performance of sharp-edge-based devices. However, simulation of sharp-edge structures in the scope of whole acoustofluidic devices is challenging due to the thin viscous boundary layer that needs to be resolved. Existing efficient modeling techniques that substitute the need for discretization of the thin viscous boundary layer through analytically derived limiting velocity fail due to large curvatures of sharp edges. Here, we combine the Fully Viscous modeling approach that accurately resolves the viscous boundary layer near sharp edges with an existing efficient modeling method in the rest of a device. We validate our Hybrid method on several 2D configurations, revealing its potential to significantly reduce the required degrees of freedom compared to using the Fully Viscous approach for the whole system, while retaining the relevant physics. Furthermore, we demonstrate the ability of the presented modeling approach to model high-frequency 3D acoustofluidic devices featuring sharp edges, which will hopefully facilitate a new generation of sharp-edge-based acoustofluidic devices.

Epitaxial growth of 2D gallium selenide flakes for strong nonlinear optical response and visible-light photodetection

Epitaxial growth of 2D gallium selenide flakes for strong nonlinear optical response and visible-light photodetection

Optical Vortex Brillouin Laser

AbstractOptical vortices, which have been extensively studied over the last decades, offer an additional degree of freedom useful in many applications, such as optical tweezers and quantum control. Stimulated Brillouin scattering (SBS), providing a narrow linewidth and a strong nonlinear response, has been used to realize quasi‐continuous wave lasers. Here, stable oscillation of optical vortices and acoustic modes in a Brillouin laser based on chiral photonic crystal fiber (PCF) is reported, which robustly supports helical Bloch modes (HBMs) that carry circularly polarized optical vortex and display circular birefringence. A narrow‐linewidth Brillouin fiber laser that stably emits 1st‐ and 2nd‐order vortex‐carrying HBMs is implemented. Angular momentum conservation selection rules dictate that pump and backward Brillouin signals have opposite topological charge and spin. Additionally, it is shown that when the chiral PCF is placed within a laser ring cavity, the linewidth‐narrowing associated with lasing permits the peak of the Brillouin gain that corresponds to acoustic mode to be measured with resolution of 10 kHz and accuracy of 520 kHz. The results pave the way to a new generation of vortex‐carrying SBS systems with applications in optical tweezers, quantum information processing, and vortex‐carrying nonreciprocal systems.

Deep Eutectic Solvents Synthesis of A2Sb(C2O4)Cl3 (A = NH4, K, Rb) with Superior Optical Performance

AbstractDeep eutectic solvents (DESs), which are considered as a new kind of green solvents, have been adopted for the synthesis of diverse functional materials. Herein, DESs synthesis is used to solve the problem of easy hydrolysis and oxidation of the emerging optical functional groups Sb3+ cations, producing three novel antimony chloride oxalates named A2Sb(C2O4)Cl3 (A = NH4, K, Rb). The three title compounds feature noncentrosymmetric structures consisted of [Sb(C2O4)Cl3]2– anionic clusters, which induce excellent linear and nonlinear optical properties of them. Particularly, Rb2Sb(C2O4)Cl3 exhibits a strong nonlinear optical response that is 2.1 times that of KH2PO4, as well as large calculated birefringence of 0.22@546 nm, indicating that antimony oxalates are promising optical materials. This work affords an effective strategy to settle the difficulties in crystallization of the materials including cations with low oxidation state and easy hydrolysis.