Third-order Nonlinear Coefficients Research Articles

Improved near-resonant two photon absorption of α-MnO2 nanowires surface functionalized reduced graphene oxide sheets

The versatile study of graphene derivatives has resurgence of interest on understanding its nonlinear optical response at different nanoscales. Nanostructured manganese dioxide: reduced graphene oxide (MnO2: rGO) hybrids were synthesized by reduction method by varying the content of rGO (5, 10, 15 & 20 wt%). X-ray Photoelectron Spectroscopy studies confirmed the surface functionalization of MnO2 on rGO. Field Emission Scanning Electron Microscopy (FESEM) and High-Resolution Tunnelling Electron Microscopy (HRTEM) witness that with respect to the content of rGO, the morphology of MnO2 varies radically from clusters to nanorods to nanowires over the surface of rGO sheets. Ground state absorption spectra of the hybrids have absorption edge at 268 nm corresponding to combined metal oxide charge transfer between rGO (π-π* transition of CC and n-π transition of C-O bonds) and MnO2 (d-d transition). Moreover, hierarchical MnO2 nanowire network resided on 2D rGO sheets involves broad absorption at the visible spectral domain due to polaron transition as well the localization of π- π* transited electrons that facilitates the probability of occurrence of excited state absorption. Intensity dependent open aperture Z-scan technique of the prepared hybrids using Q-switched Nd: YAG 532 nm nanopulsed laser reveals unusual transitions and enhanced nonlinear absorption. MnO2:(5 wt%) rGO shows saturable absorption (SA) at low intensity and changeover dynamically to reverse saturable absorption (RSA) at higher intensity. MnO2:(10 & 15 wt%) rGO exposes coupled nonlinear absorption (SA + RSA) owing to the combined effect of graphene (π-states) and MnO2 (σ-states). MnO2:(20 wt%) rGO exhibits a stronger RSA ascribed to sequential two photon absorption. The third-order nonlinear absorption coefficient and limiting threshold of MnO2: rGO (20 wt%) are 4.04 ×10-10 m/W and 0.84 ×1012 W/m2, which shows five-fold increase compared to bare rGO and MnO2. The obtained results propose that the optical nonlinearity of MnO2 nanowires surface functionalized rGO sheets can significantly be tuned to meet the requirements for fabricating laser safety devices.

Effect of the nonlinear dispersive coefficient on time-dependent variable coefficient soliton solutions of the Kolmogorov-Petrovsky-Piskunov model arising in biological and chemical science

In this article, we study the soliton solutions with a time-dependent variable coefficient to the Kolmogorov-Petrovsky-Piskunov (KPP) model. At first, this model was used as the genetics model for the spread of an advantageous gene through a population, but it has also been used as a number of physics, biological, and chemical models. The enhanced modified simple equation technique applies to get the time-dependent variable coefficient soliton solutions from the KPP model. The obtained solutions provide diverse, exact solutions for the different functions of the time-dependent variable coefficient. For the special value of the constants, we get the kink, anti-kink shape, the interaction of kink, anti-kink, and singularities, the interaction of instanton and kink shape, instanton shape, kink, and bell interaction, anti-kink and bell interaction, kink and singular solitons, anti-kink and singular solitons, the interaction of kink and singular, and the interaction of anti-kink and singular solutions to diverse nature wave functions as time-dependent variable coefficients. The presented phenomena are clarified in three-dimension, contour, and two-dimension plots. The obtained wave patterns are powerfully exaggerated by the variable coefficient wave transformation and connected variable parameters. The effect of second-order and third-order nonlinear dispersive coefficients is also explored in 2D plots.

Investigation of linear and nonlinear optical properties in quantum dots: Influence of magnetic and AB flux fields

In the present work, analytical expressions for the energy eigenvalues and eigen functions are obtained by solving the radial Schrödinger equation for inverse quadratic Hellmann plus Yukawa (IQHY) potential using Nikiforov-Uvarov functional analysis method. As an application part of this work, expressions for the linear and third-order nonlinear absorption coefficients and refractive index changes are computed to study the optical properties of the spherical GaAs quantum dots. We extend the investigation of the IQHY potential by incorporating the effects of magnetic and Aharonov–Bohm (AB) flux fields. Our results reveal that the optical properties of the GaAs quantum dots are strongly influenced by variations in the dot radius, potential height and intensity of incident photons. Specifically, we observe that the introduction of magnetic and AB flux fields significantly alters the energy eigenvalues and eigenfunctions, leading to distinct optical characteristics. The results of present study are found in consistent with other theoretical studies available in the literature.

Unravelling anisotropic nonlinear shear elasticity in muscles: Towards a non-invasive assessment of stress in living organisms

Acoustoelasticity theory describes propagation of shear waves in uniaxially stressed medium and allows the retrieval of nonlinear elastic coefficients of tissues. In transverse isotropic medium such as muscles the theory leads to 9 different configurations of propagating shear waves (stress axis vs. fibers axis vs. shear wave polarization axis vs. shear wave propagation axis). In this work we propose to use 4 configurations to quantify these nonlinear parameters ex vivo and in vivo. Ex vivo experiments combining ultrasound shear wave elastography and mechanical testing were conducted on iliopsoas pig muscles to quantify three third-order nonlinear coefficients A, H and K that are possibly linked to the architectural structure of muscles. In vivo experiments were performed with human volunteers on biceps brachii during a stretching exercise on an ergometer. A combination of the third order nonlinear elastic parameters was assessed. The knowledge of this nonlinear elastic parameters paves the way to quantify in vivo the local forces produced by muscle during exercise, contraction or movements.

Polarization Z-Scan Studies Revealing Plasmon Coupling Enhancement Due to Dimer Formation of Gold Nanoparticles in Nematic Liquid Crystals.

We investigate the plasmon coupling of gold nanoparticle (AuNP) dimers dispersed in a nematic liquid crystal matrix using the polarization z-scan technique. Our experimental setup includes the precise control of incident light polarization through polarization angles of 0°, 45°, and 90°. Two distinct cell orientations are examined: parallel and twisted nematic cells. In parallel-oriented cells, where liquid crystal molecules and AuNPs align with the rubbing direction, we observe a remarkable 2-3-fold increase in the nonlinear absorption coefficient when the polarization of the incident light is parallel to the rubbing direction. Additionally, a linear decrease in the third-order nonlinear absorption coefficient is noted as the polarization angle varies from 0° to 90°. In the case of twisted nematic cells, the NPs do not have any preferred orientation, and the enhancement remains consistent across all polarization angles. These findings conclusively establish that the observed enhancement in the nonlinear absorption coefficient is a direct consequence of plasmon coupling, shedding light on the intricate interplay between plasmonic nanostructures and liquid crystal matrices.

TiN/Ti3C2 Heterojunction Microfiber-Enhanced Four-Wave Mixing-Based All-Optical Wavelength Converter

As a novel nanomaterial, the TiN/Ti3C2 heterojunction has been demonstrated to possess exceptional optoelectronic properties, offering significant potential for applications in fields such as communication, optical sensors, and image processing. The rapid evolution of the internet demands higher communication capacity and information processing speed. In this context, all-optical wavelength conversion, a pivotal technique in all-optical signal processing, holds paramount importance in overcoming electronic bottlenecks, enhancing wavelength utilization, resolving wavelength competition, and mitigating network congestion. Utilizing the idle light generated through the four-wave mixing (FWM) process accurately mimics the bit patterns of signal channels. This process is inherently rapid and theoretically capable of surpassing electronic bottlenecks with ease. By placing an optical filter at the fiber output end to allow idle light passage while blocking pump and signal light, the output becomes a wavelength-converted replica of the original bitstream. It has been verified that TiN/Ti3C2 heterojunction-coated microfiber (THM) exhibits outstanding third-order nonlinear coefficients. Building upon this, we achieved a THM-enhanced FWM all-optical wavelength converter, resulting in a ~4.48 dB improvement in conversion efficiency. Compared to conventional high-nonlinear fibers, this compact device significantly reduces fiber length and can be easily integrated into current high-speed optical communication networks. It demonstrates broad prospects in the realms of all-optical signal processing, robotic applications, ultra-high-speed communication, and beyond.

Impact of intense laser Bessel beam on excitonic complexes in ellipsoidal quantum dot

This theoretical study investigates the response of a strongly oblate GaAs ellipsoidal quantum dot to an intense laser field with a Bessel intensity profile at non-resonant extreme violet and simultaneously resonant mid-infrared laser irradiation. Mainly, the linear and nonlinear optical properties of biexcitons in quantum dot are observed. Due to the complexity of the considered particle, all calculations are performed in the framework of the variational method. Biexciton variational function is constructed on the one-particle wave functions, which are correlated with each other by exponents with variational parameters. The biexciton energies for different values of applied intense laser field magnitude on the small geometrical parameter of ellipsoidal quantum dot are calculated. The nonlinear optical properties, including the oscillator strength, third-order nonlinear susceptibility, absorption coefficient, and refractive index change, are evaluated. Numerical results reveal the dependence of the exciton and biexciton energies on the intensity of the laser field and the geometrical parameters of the quantum dot. Additionally, the dependencies of the third-order susceptibility, absorption coefficient, and induced refractive index change on photon energy near the one-photon resonance and two-photon resonance are analyzed. The two-photon absorption coefficient of the biexciton in GaAs ellipsoidal quantum dot is computed, and the spectra of refractive index changes induced by biexciton transitions between ground states are analyzed for different magnitudes of the intense laser field. Biexciton recombination radiative lifetime on the small semiaxis of the ellipsoidal quantum dot for the different values of the laser field influence is estimated. Finally, the visualization of the localization region of biexciton in the ellipsoidal quantum dot is performed.

Thickness-Dependent nonlinear optical absorption of InSe/Graphene van der Waals heterostructures

InSe/Graphene van der Waals heterostructures emerge as promising candidates for optoelectronic applications. In this work, we systematically examine the saturable absorption properties of InSe/Graphene heterostructures with varying thickness of InSe. We establish a positive correlation between the third-order nonlinear absorption coefficient and heterostructure thickness. Furthermore, we uncover the interplay of carrier dynamics within the heterostructures, revealing prolonged interlayer transfer times and slowed carrier relaxation as InSe thickness increases. These insights shed light on the potential of InSe/Graphene heterostructures for advanced optoelectronic devices, fostering further advancements in this field.

Ultrafast nonlinear optical properties of Ag/WTe2 composite films

WTe2 thin films and Ag/WTe2 composite films were successfully prepared by magnetron sputtering technology. The nonlinear absorption (NLA) characterization of the Ag/WTe2 composite system at 532 nm was also investigated by the ps Z-scan technique. The results show that both WTe2 films and Ag/WTe2 composite films exhibit saturable absorption (SA) effect and self-dispersion phenomenon. In addition, the nonlinear absorption performance of the composite films are significantly enhanced compared to that of a single WTe2. With the increase of Ag sputtering power, their third-order nonlinear absorption coefficients β increase by one order of magnitude, indicating that Ag enhances the nonlinear absorption performance of Ag/WTe2 composite films. This study provides a new idea for the application of Ag/WTe2 composite films in optoelectronic devices.

Chitosan, a Cationic Polymer-Loaded CuS:Ni Nanoparticles Well Suited for Pseudocapacitors, Optical Switching and Spintronic Devices

Chitosan, a cationic polymer, is loaded on Ni-doped copper monosulfide (CuS) NPs with optimal Ni doping concentration, and electrochemical, third-order nonlinear, magnetic and antibacterial characteristics of chitosan unloaded and loaded CuS:Ni nanoparticles are compared. The crystallite size of pure CuS increased with Ni doping and the 10[Formula: see text]wt.% Ni-doped CuS NPs exhibit a maximum crystallite size of 41[Formula: see text]nm. The presence of Ni in the doped samples was acknowledged by the existence of Ni 2p[Formula: see text] and Ni 2p[Formula: see text] peaks at binding energies 851[Formula: see text]eV and 873.1[Formula: see text]eV, respectively from the XPS spectrum. Optical reflectance decreased with Ni doping and the optical band gap varied from 2.56[Formula: see text]eV to 2.4[Formula: see text]eV. Specific capacitance increased with Ni doping. Diamagnetic nature of CuS changed to ferromagnetic with Ni doping. The 10[Formula: see text]wt.% Ni-doped CuS exhibits a high third-order nonlinear absorption coefficient and susceptibility value. Bacterial growth inhibition nature of CuS improved with Ni doping. Among the doped samples, the 10[Formula: see text]wt.% Ni-doped sample exhibits improved electrochemical, third-order nonlinear, magnetic and antibacterial properties. Keeping this as the optimized Ni concentration, chitosan was loaded. Chitosan-loaded samples exhibited a reduction in crystallite size and an increase in band gap. A high specific capacitance of 96[Formula: see text]F/g was realized for the chitosan-loaded sample. Saturation magnetization of 10[Formula: see text]wt.% CuS:Ni decreased with chitosan loading.

Excellent Nonlinear Optical Limiting Behavior of Tetra (C60) Lanthanum Phthalocyanine in Solid Poly(methyl methacrylate) Films

This work reports on the exceptional optical limiting performance of a novel D–A-type compound, namely, LaPc-4(C60), wherein the lanthanide phthalocyanine is used as a donor and four C60 are used as acceptors. In addition, phenyl ether bonds were introduced into the molecule, making it semirigid and increasing its solubility. At the same time, the phenyl ether bond could act as a π-electron bridge, which increases the electron transfer pathway, expands the π-conjugated system, and reduces the spatial site resistance of the molecule. Furthermore, the uniform poly(methyl methacrylate) (PMMA) composite film (LaPc-4(C60)/PMMA) was prepared by a simple solution casting method. In comparison with individual C60 or LaPc(CHO)4, both LaPc-4(C60) in solution and in the solid PMMA composite film exhibited larger third-order nonlinear absorption coefficients and lower limiting thresholds at 532 nm. In particular, LaPc-4(C60)/PMMA exhibits huger nonlinear absorption coefficient (2900 cm/GW) and larger third-order susceptibility (4.91 × 10–9 esu), which can be attributed to the synergistic effect of the different non-linear absorption mechanisms and efficient photoinduced electron transfer process between C60 and LaPc.

Third-order optical nonlinearity and multiferroicity of nanoparticles thin films of isovalent rare earth Y3+ ion substituted BiFeO3

Present work reveals the multiferroic and nonlinear optical properties of pristine and Yttrium (Y3+) substituted BiFeO3 nanoparticles synthesized by sol-gel technique, and fabricated thin films of the nanoparticles. The nanoparticles thin films were deposited on glass substrates with an average thickness of 85 nm by the thermal evaporation method in a high vacuum of 10−6 Torr. The structural and morphological studies were done by using XRD, Fullprof, XPS, AFM, FESEM and TEM with SAED. Further BET method was used to find out the surface area, pore size and pore volume of the nanoparticles. The multiferroic properties of Bi1-xYxFeO3 (x = 0.0, 0.5, 0.10, 0.15) have been investigated using VSM (magnetic) and P-E loop tracer (electrical). The doping of magnetic Y3+ions in host BiFeO3 nanoparticles modified and improved the optical, structural, multiferroic properties enormously. Linear optical properties were characterized by UV–Visible, Raman, and Photoluminescence. Third-order nonlinear absorption coefficient (β) and the imaginary part of third-order susceptibility (χi3) of Bi1-xYxFeO3 (x = 0.0, 0.5, 0.10, 0.15) have been investigated using a single beam Z-scan technique with a continuous wave (CW) diode laser of 520 nm wavelength. The films exhibit saturation absorption (SA) behavior and it increases on increasing the Yttrium (Y3+) substitution in BiFeO3. Thus, the NLO behavior of the films makes it an auspicious material for application in optoelectronic devices.

Highly efficient coherent detection of terahertz pulses based on ethanol

Water-based terahertz (THz) coherent detection scheme has been recently proposed, which overcomes the bandwidth limitation or high probe laser power demand in solid-/gas-based schemes. Here, we report a highly efficient THz coherent detection method using ethanol with superior performances under the mechanism of four-wave mixing. We systematically investigate the energy ratios and relative polarizations between the THz-induced second harmonic and control second harmonic (CSH) beams and reveal that ethanol always exhibits significantly higher detection sensitivity than water. The coherent, incoherent, or hybrid detection mode can be flexibly switched by changing the CSH beam polarization. The enhanced sensitivity derives from the much larger third-order nonlinear coefficient and lower ionization potential of ethanol. In addition, for the ethanol–water mixtures with various concentrations, the THz coherent detection signals can always be decomposed into the linear superposition of those from pure ethanol and neat water at the sub-picosecond timescale, indicating the synergistic contribution of ethanol and water molecules in the mixture during the detection process. This work provides a valid method to significantly improve the sensitivity of the liquid-based coherent detection scheme and a research perspective for exploring the solute–solvent molecular interactions.

Pulsed heterodyne interferometry for nonlinear SOI waveguide characterization

Silicon waveguides are a promising candidate for integrated nonlinear optics applications. Nonlinear coefficients of Silicon on Insulator (SOI) waveguides have been previously measured using techniques such as Z-scan, D-scan, Four Wave Mixing (FWM) and Self-phase modulation. However, they have several drawbacks such as they operate at high power or are cumbersome to setup and require multiple measurements to determine all the coefficients. In this work, we develop a direct and single measurement technique to characterize the nonlinear processes in SOI waveguides. This is achieved by employing a heterodyne interferometric technique to accurately measure minute nonlinear response. The measured nonlinear amplitude and phase shifts are fit to extract third-order nonlinear coefficients of Two-photon absorption, Kerr nonlinear index, Free carrier absorption and Free carrier dispersion. The obtained coefficients for SOI waveguides are close to that found in literature measured using the above-mentioned techniques. The advantages of this method include easy interpretation of the output signal and relatively low power of operation. It is especially advantageous for studying materials such as Phase Change Materials (PCM) in which phase changes occur dynamically. This aspect is quite promising for characterizing emerging materials for integrated photonics applications.

A remarkable third-order nonlinear optical behavior of single-crystal bromide organic-inorganic lead halide perovskite

The optical and structural aspects of methylamine lead bromide (MAPbBr3) single crystal (SC) are investigated. Based on Kramers–Kronig (KK) equations, the optical and dielectric parameters are investigated. The optical phonons Longitudinal optical (LO = 678 cm−1) and Transversal optical (TO = 578 cm−1) phonon modes are associated with the optical interaction with lattices in the visible region for MAPbBr3 SC. The Z-scan method is used to investigate the third-order nonlinear coefficients of SC hybrid organic–inorganic lead halide perovskites, MAPbBr3 with the 2.19 eV optical band gap energy. According to the nonlinear optical (NLO) properties, MAPbBr3 has a high third-order NLO response. The two-photon absorption (2PA) coefficient is found to be 3 × 10-4 cm W−1 using the transmission open aperture Z-scan technique. The nonlinear refraction (NLR) is obtained in the order of 10-9 cm2 W−1 utilizing a close aperture Z-scan, which revealed self-defocusing phenomena. This research shows that MAPbBr3 is a practical and low-priced nonlinear material for ultrafast photonics applications.

Effect of Gaussian and Bessel laser beams on linear and nonlinear optical properties of vertically coupled cylindrical quantum dots

Vertically coupled quantum dots are one of the most interesting and promising structures, which find application in a wide range of fields. Particularly, they are noteworthy candidates as a source of single photon and entangled photon pair sources, as qubits and quantum gates in quantum computation, etc. Various external perturbations can act as an instrument for the manipulation of the properties of these structures and an intense laser field is a great example of this. In this work, vertically coupled cylindrical quantum dots made of InAs in a GaAs matrix with a modified Pöschl–Teller potential have been considered under intense laser fields with two laser beam profiles: Gaussian and Bessel. The energy levels and wave functions have been obtained for this structure. Linear and third-order nonlinear absorption coefficients, refractive index changes and second and third harmonic generation susceptibilities have been investigated at different temperatures and for different values of the laser parameters.

Theoretical investigation of laser field effect on nonlinear optical properties of quantum dots

In this work, we have theoretically investigated the effects of a high-frequency intense laser field on the nonlinear optical properties of a two-dimensional Gaussian quantum dot system. A non-resonant monochromatic intense laser field with circular polarization applied to the system is considered in the framework of a non-perturbative approach. The nonlinear optical properties of the system have been investigated by using the compact-density matrix approach and iterative procedure. The laser field effect on the linear and the third-order nonlinear absorption coefficients and refractive index changes have been examined. Results reveal that the optical characteristics of the two-dimensional Gaussian quantum dot system are considerably influenced by the strength of the intense laser field in addition to structure parameters.

Large-area vapor-deposited Cs3Cu2I5 perovskite thin films for highly effective third-order nonlinear optics

Zero-dimensional (0D) lead-free perovskites hold promise for efficient optoelectronic and photonic devices, but there are still critical challenges in fabricating large-area, high-quality thin films for practical applications. Herein, we report a simple vapor route to prepare 0D lead-free Cs3Cu2I5 perovskite thin films of high optical quality over large areas. Importantly, the deposition approach can be applied to diverse substrates, including mica, fused silica, MgO, and indium tin-oxide (ITO) coated glass. The deposited Cs3Cu2I5 thin films are phase pure and highly uniform. These Cs3Cu2I5 thin films exhibit strong blue emission upon UV light illumination, a broad band centered at 445 nm assigned to the self-trapped exciton emission. Furthermore, third-order nonlinear optical properties of the as-prepared thin films were determined by means of the Z-scan method. These thin films showed the third-order nonlinear absorption coefficient β as ∼ 1.07 × 10−7 m/W, which is five orders of magnitude larger than three-dimensional counterpart, CsPbI3. Thus, we demonstrate that large-area, high-quality Cs3Cu2I5 thin films can be vapor-deposited and have great potentials in optical switching and optical limiting applications.

Temporal Contrast Enhancement Based on the Self-Diffraction Process with Different Kerr Media

In this study, the self-diffraction (SD) process proved to be a competitive method to achieve a seed pulse with high temporal contrast in ultra-intense lasers. Several different nonlinear, transparent Kerr media including BK7 glasses, AL2O3 and CVD diamonds were compared experimentally to obtain SD signals with high energy and high conversion efficiency. AL2O3, with a high third-order nonlinear coefficient and high laser damage threshold, was found to be the best medium to improve the conversion efficiency of SD signals. The highest first-order SD signal of 401.7 μJ was achieved, with the conversion efficiency at approximately 9.1%, when the incident pulse energy was 4.40 mJ. The temporal contrast of the obtained first-order SD signal was improved by 7 orders of magnitude to 1012. As a result, this cleaning pulse will facilitate research involving ultra-intense laser systems and high-intensity laser–matter interactions.

Comparison of sensitivity in nonlinear ultrasonic detection based on Lamb wave phase velocity matching mode

ABSTRACT In nonlinear ultrasonic damage detection, the appropriate Lamb wave mode to accurately characterise the nonlinearity attributed to the material damage should be selected important. However, an effective mode is more difficult to select practically as impacted by the dispersion and multi-mode characteristic of the Lamb wave. In this study, based on the dispersion curve of Lamb waves, the modes meeting the second harmonics and third harmonics phase velocity matching were given, and the nonlinear cumulative effects exerted by different modes on fatigue cracks were compared. In addition, an investigation was conducted on the amplitude change of the second and third harmonics signal of the identical fatigue damage. The results show that the harmonic amplitude decreases with the increase of the fatigue crack length. The third harmonics under the two modes are more sensitive to fatigue damage than the second harmonics. Moreover, the amplitude of the third harmonic excited by S1 mode exceeds that of the other mode. As the fatigue crack length increases, the relative second- and third-order nonlinear coefficients generated by S1 mode have approximately the same trend, first increasing and then decreasing. The results reveal that the third harmonic under S1 mode could more effectively characterise fatigue damage.