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We construct a new exact solution of the problem of a filament placed parallel to the interface between two insulators, one of which has a nonlinear susceptibility. [ABSTRACT FROM AUTHOR]

Miller's rule is an empirical relation between the nonlinear and linear optical coefficients that applies to a large class of materials but has only been rigorously derived for the classical Lorentz model with a weak anharmonic perturbation. In this work, we extend the proof and present a detailed derivation of Miller's rule for an equivalent quantum-mechanical anharmonic oscillator. For this purpose, the classical concept of velocity-dependent damping inherent to the Lorentz model is replaced by an adiabatic switch-on of the external electric field, which allows a unified treatment of the classical and quantum-mechanical systems using identical potentials and fields. Although the dynamics of the resulting charge oscillations, and hence the induced polarizations, deviate due to the finite zero-point motion in the quantum-mechanical framework, we find that Miller's rule is nevertheless identical in both cases up to terms of first order in the anharmonicity. With a view to practical applications, especially in the context of ab initio calculations for the optical response where adiabatically switched-on fields are widely assumed, we demonstrate that a correct treatment of finite broadening parameters is essential to avoid spurious errors that may falsely suggest a violation of Miller's rule, and we illustrate this point by means of a numerical example. [ABSTRACT FROM AUTHOR]

Organic imidazolium hydrogen fumarate (IHF) crystals are grown using the slow evaporation method. The IHF has triclinic crystal structure. The 1H NMR spectrum has five chemical shifts for the IHF crystal. The band at 3155 cm−1 in IR occurs due to the presence of O─H stretching vibration of the IHF molecule. The bandgap value of the IHF crystal is determined to be 4.6 eV. The intense violet emission band is noted at 361 nm. The IHF crystal has thermal stability value of 179 °C. Hirshfeld surface is used to find out the different intermolecular interactions of the IHF crystal. The HOMO–LUMO energy gap is determined to be 4.70 eV. The hydrogen atoms have positive potential in the MEP analysis. The high stabilization energy of 56.81 kcal mol−1 is noticed for π*(C1─N7) → π*(C2─C3) interaction. The third‐order NLO susceptibility (χ(3)) of the IHF is 2.08934 × 10−9 esu. [ABSTRACT FROM AUTHOR]

The electronic properties of ZnIn2Se4 crystals have been studied experimentally by spectral ellipsometry and theoretically (from the first principles) using the density functional theory (DFT). Ellipsometric studies in the energy range of 0.7–6.5 eV made it possible to determine the imaginary and real parts of the dielectric function and optical conductivity, as well as the dispersion of the refractive indices, extinction coefficients, and absorption coefficients, and to estimate the values of the Urbach energy, plasma frequency, and nonlinear optical characteristics of ZnIn2Se4 crystals. The electronic band structure, origin of energy states, optical functions for incident light polarized along the crystal optic axis and perpendicular to it, and partial densities of states projected onto atoms are determined by ab initio calculations. The theoretical results are compared with the experimental data obtained by spectral ellipsometry. [ABSTRACT FROM AUTHOR]

Measuring the nonlinear responses of living cells has enabled an understanding of their behavior and functionality. Currently, this response has been studied at radio and optical frequencies, leaving an unexplored gap in the field of microwaves. This paper presents a system that combines microwave technology with a microfluidic platform to measure the nonlinear susceptibility of living organisms to electromagnetic fields. The applied technique involves feeding the system with two tones (2.1 GHz and 4 GHz) to generate third-order intermodulation products (PIMP) at 5.9 GHz. Nonlinear susceptibility was measured from the power levels of PIMP using a spectrum analyzer. Broadband electrodes based on the slot bowtie geometry were manufactured to operate at 5 GHz with a bandwidth of 4 GHz. Additionally, an engineering process is presented to optimize the power of the internal mixer of the spectrum analyzer to obtain the maximum dynamic range and improve the sensitivity of the system. Nonlinear susceptibility to microwaves was analyzed in four samples: pure ethanol, a mixture of ethanol and dimethyl sulfoxide (DMSO), live Escherichia coli (E. coli), and heat-killed E. coli. The results show that ethanol has zero nonlinear susceptibility, whereas when it is mixed with DMSO, a nonlinear response appears at a value of 4 dB with respect to the nonlinear susceptibility of the system in the absence of a sample. Finally, the nonlinear susceptibility of live E. coli to microwaves was detected, with a difference of 8 dB over the reference value and 6 dB with respect to the heat-killed E. coli sample.

We extend the nonstandard (NS) finite difference time domain (FDTD) methodology, originally developed to solve Maxwell's equations in linear materials, to nonlinear ones. We validate it by computing harmonics generation in a nonlinear dielectric and comparing with theory. The methodology also applies to the quantum electrodynamics that describes the interaction of charged particles with electromagnetic fields, and also to the Ginzburg-Landau model of superconductivity. [ABSTRACT FROM AUTHOR]

In this study, the effects of gamma radiation with doses ranging from 0 KGy to 100 KGy on the structural and optical properties of the Beta Metal-free Phthalocyanine (β-H2Pc) powder and films were investigated. X-ray diffraction and scanning electron microscope were used to examine the crystalline and morphological structures of the thin films. While Fourier transform infrared and absorption spectra were utilized to study the changes in molecular structure and energy absorption, respectively. The results showed that while γ-irradiation induced changes in the surface morphology and optical properties of β-H2Pc, the molecular structure remained stable except for the disappearance of the hydroxyl (OH) functional group peak. The irradiation dose was found to affect the dielectric constants, dispersion characteristics, and nonlinear optical susceptibility of the material. The β-H2Pc thin films exhibited high absorption coefficients and refractive index values, making them promising candidates for optoelectronic devices such as solar cells. However, careful consideration of the effects of gamma irradiation on other properties of β-H2Pc such as stability, toxicity, and cost-effectiveness is necessary. [ABSTRACT FROM AUTHOR]

The present article demonstrates the photophysical and nonlinear optical studies of the chromophore 2,2'-(hexane-1,6-diylbis(9 H-carbazole-9,3-diyl))bis(ethene-1,1,2-tricarbonitrile (HCzN). The structure and the purity of the synthesized molecule have been confirmed via Infrared (IR) and Nuclear Magnetic Resonance (NMR) spectroscopies. Absorption and emission spectroscopies have been performed to understand the photophysical properties and we have enumerated the absorption coefficient (α0), refractive index (n0), optical bandgap (Eg), and optical conductivity (σ) for this chromophore. We have also explored the third-order nonlinear optical (NLO) characteristics of HCzN at the concentrations of 1, 2, 3, and 4 mM employing both closed and open-aperture Z-scan methods at 25 mW laser power. This chromophore evinces the self-defocusing and saturable absorption nature for closed and open aperture scans respectively. The calculated NLO parameters such as the coefficients of nonlinear refraction (n2) and nonlinear absorption (β) are found to be of the order of 10−6 cm2/W and 10−3 cm/W respectively with the nonlinear optical susceptibility (χ(3)), and hyperpolarizability (γ) of the order of 10−5 esu and 10–27 esu respectively. The magnitude of NLO parameters varies linearly concerning the concentration. The enhanced values of NLO parameters of chromophore HCzN shows its potential in photonic applications. [ABSTRACT FROM AUTHOR]

We present a study of high efficient terahertz (THz) wave generation in DASB/GaAs, DASC/GaAs, and DAST/GaAs multilayer structures at 1.5THz via difference frequency generation (DFG) process with 1.5µm femtosecond laser pulses. We also compare the conversion efficiency in proposed structures with DASB/SiO2, DASC/SiO2, and DAST/SiO2 multilayer structures and bulk crystals DASB, DASC, and DAST. These structures compensate for phase mismatching in bulk crystals DASB, DASC, and DAST and increase conversion efficiency from 10-5 in bulk organic crystals up to 10-3 in multilayer structures. We show that DASC/GaAs is the best structure to generate 1.5THz waves.

As a representative transition metal oxide, cupric oxide (CuO) has attracted a lot of interest in miscellaneous fields. In the present work, the prominent third-order nonlinear optical (NLO) features of CuO nanosheets were demonstrated via the typical Z-scan technique at 1 μm. The open-aperture (OA) Z-scan measurements at different intensities clearly showed that CuO nanosheets possessed the saturable absorption (SA), reverse saturable absorption (RSA) and optical limiting behaviors. The closed-aperture (CA) Z-scan technology was implanted to investigate the nonlinear refractive index and the third-order nonlinear susceptibility. In virtue of the strong nonlinear optical absorption properties of CuO nanosheets, a stable all-solid-state mode-locked laser with the as-prepared CuO nanosheets as saturable absorber at 1.06 μm was realized for the first time. Our work confirmed that CuO nanosheets exhibited outstanding NLO properties, which might stimulate the development in ultrafast photonics and nonlinear optics.

The nonlinear optical response of graphene oxide quantum dots (GOQDs) fabricated by the carbonization and exfoliation of electrospun polyacrylonitrile (PAN) fibers is reported. Electrospun and carbonized fibers were characterized by SEM and XPS. SEM micrograph confirmed the formation of PAN fibers of 153.44 ± 6.44 nm, while by XPS the binding energies associated with sp2 and sp3 carbon hybridizations were found, after the carbonization process. On the other hand, the GOQDs obtained were characterized by photoluminescence (PL), UV–Vis, Raman spectroscopy, and High-Resolution Transmission Electron Microscopy (HRTEM). The GOQDs size of 10 nm was estimated by HRTEM. Raman spectroscopy showed the D and G bands associated with the sp2 and sp3 hybridizations of the GOQDs, by PL two energy values of 2.67 and 2.97 eV were calculated. The UV–Vis spectrum showed two absorption bands confirming the presence of GOQDs. The nonlinear characterization was carried out using the P-scan technique, previously photodepositing GOQDs onto an optical fiber, using a coherent radiation source at a wavelength of 1550 nm. The results obtained showed a saturable absorption behavior with a value of β=−2.474×10−4m/W and a nonlinear susceptibility of χ(3)≈−7.749×10−4(esu). The results of this work showed that GOQDs obtained can be used for optical switching applications.

The linear dynamic susceptibility is arguably the most important property to specify the magnetization dynamics of a given system. Therefore, this quantity has been studied in great detail and the corresponding measurements known as susceptometry are well-established. Notwithstanding its relevance, the linear susceptibility is inherently limited to describe the magnetization response to weak external fields only. Here, we suggest the framework of Medium Amplitude Field Susceptometry (MAFS) to study the non-linear response which complements the linear susceptibility and provides additional information on the magnetic properties of the system and is applicable to magnetic fields of medium amplitudes. In particular, we introduce the general third-order nonlinear susceptibility χ ˆ 3 as a central quantity that completely specifies the lowest-order non-linear response to arbitrary time-dependent magnetic fields. We show that response functions in medium amplitude oscillatory magnetic fields and parallel superposition susceptometry are contained in χ ˆ 3 as special cases. Also included in χ ˆ 3 are interesting intermodulation effects when the system is probed by a superposition of oscillating magnetic fields with different frequencies. We work out the explicit form of χ ˆ 3 for several model systems for the dynamics of magnetic nanoparticles (MNPs). We expect this unifying framework to be not only of theoretical interest, but also useful for a deeper characterization of MNP systems, giving additional information on their suitability for various applications. [Display omitted] • Extend traditional alternating current (AC) susceptometry from the linear regime to magnetic fields of moderate amplitude. • Introduce third-order nonlinear susceptibility χ ˆ 3 (ω 1 , ω 2 , ω 3) as central new quantity. • Weakly nonlinear regime fully specified by χ ˆ 3 for arbitrary time-dependent fields. • Mean amplitude and parallel superposition susceptometry are special cases of χ ˆ 3. • Intermodulation effects provide additional insights. • Explicit form of χ ˆ 3 (ω 1 , ω 2 , ω 3) worked out for particular model systems of magnetic nanoparticles. [ABSTRACT FROM AUTHOR]

The study is based on annealing-induced Bi diffusion into Se 30 S 30 Sb 40 sites that bring modification in its linear-nonlinear optical, structural, and dielectric properties. The Bi/Se 30 S 30 Sb 40 heterostructure film was annealed at 100,150,200 and 250 °C. The Bi 2 Se 3 and Sb 2 Se 3 phase formation was confirmed from the X-ray diffraction as well as from the Raman study. The morphology has been studied by the field emission scanning electron microscopy images with increased particle size upon annealing. The uniformity and homogeneity of the film were noticed from the energy dispersive X-ray analysis elemental mapping. The bandgap decreased from 1.461 eV (as-prepared Bi/Se 30 S 30 Sb 40) to 1.258 eV (250 °C annealed) with an increment in static refractive index from 2.864 to 3.114 which was noticed from the optical study. The linear optical parameters were tuned with annealing conditions and such changes were understood from the concept of density of states and defects in the film. The increase in dielectric loss factor and decrease in quality factor with annealing is accompanied by the increase in both electronic and optical conductivity. The plasma frequency decreased and optical electronegativity reduced from 1.728 (as-prepared Bi/Se 30 S 30 Sb 40) to 1.692 (250 °C annealed) with annealing. The value of 3rd-order nonlinear susceptibility and non-linear refractive index gets almost doubled (i.e. 1.838 × 10−11 to 3.913 × 10−11 esu and 2.419 × 10−10 to 4.735 × 10−10 esu respectively) with annealing with an increase in the nonlinear absorption coefficient. The hydrophilic nature of the films with annealing was observed from the surface wettability study. The computational study by density functional theory provided the necessary idea for structural and physical parameters of the films. [Display omitted] • Increase in nonlinear refractive index and 3rd order nonlinear susceptibility upon annealing Bi/Se 30 S 30 Sb 40 films. • Optical electronegativity decreased and the nonlinear absorption coefficient increased. • Films became more hydrophilic in nature after annealing. • Decrease in the optical bandgap is due to a change in the local structure. • Increase in dielectric constants is suitable for dielectric applications [ABSTRACT FROM AUTHOR]

The present study extensively investigates the optical and structural properties of β-H 2 Pc thin films before and after annealing at temperatures of 373, 423, 473, 523, and 573 K/1 h, enabling the design of efficient organic-based devices. The mean crystallite size was calculated from XRD and found to be 8.5 nm at 300 K, which increased as the annealing temperature increased, confirming the crystallinity improvement upon annealing. In addition, the SEM images revealed that the grain size increased with increasing annealing temperature. The FTIR results confirmed the high thermal and chemical stability upon annealing. Furthermore, increasing the annealing temperature leads to a decrease in the transmittance spectrum and an increase in the reflectance spectrum. The results revealed a decrease in the optical band gap of β-H 2 Pc films from 1.472 eV to 1.406 eV for the onset gap and from 2.44 to about 2.21 eV for the fundamental gap with increasing annealing temperature to approximately 573 K. Moreover, the nonlinear optical parameters show an increase with higher thermal treatment temperatures. The annealing process has a significant impact on the optical and structural properties, leading to noticeable variations at specific annealing temperatures. [Display omitted] [ABSTRACT FROM AUTHOR]

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. • Investigation of biexciton states in quantum dot under intense Bessel laser. • Calculations of biexciton energies using the variational method. • Investigation of one-photon and two-photon resonances transitions. • Estimation of recombination lifetimes and visualization of localization. [ABSTRACT FROM AUTHOR]

The influence of 532 nm laser irradiation on the optical changes of Ag 2 S/As 2 Se 3 thin films. The irradiation influenced the linear and the nonlinear optical parameters. [Display omitted] • 532 nm laser irradiation on Ag 2 S/As 2 Se 3 thin films has been investigated. • The optical stability of the film under prolonged irradiation is observed from the small change (<10%). • The nonlinearity (χ(3) and n 2) increased with irradiation time. • The optical conductivity and dielectric parameters increased with irradiation time. • Electrical susceptibility decreased with the decrease in nonlinear absorption coefficient (β c). The time dependent laser induced effects on the linear and nonlinear optical properties of Ag 2 S/As 2 Se 3 heterostructure films has been investigated in the current study. The Ag-S-Se-As solid solution formed from the intermixing of Ag 2 S and As 2 Se 3 layers brings changes in the absorption edge and other optical parameters. The increase in transmittance gradually saturated followed by small increase in absorbance. The reduction in bandgap from 1.572 eV to 1.52 eV is due to the increase in defect states and disorder in the film because of the intermixing of two layers. The static refractive index is increased by 6.03% which enhanced the nonlinear refractive index by 38% upon laser irradiation. The optical conductivity increased while the electrical susceptibility decreased with the increase in laser irradiation time duration. The dielectric loss factor increased that reduced the quality factor. The increase in carrier concentration reduced the optical electronegativity upon laser irradiation. The third order nonlinear susceptibility (χ(3)) is doubled at 120 min. laser irradiation. The amorphous nature remains unchanged with laser irradiation as probed by XRD and Raman study. The surface roughness is not much changed as found from AFM study. The stability in structure and morphology of the films make them appropriate candidate for optoelectronic applications, in particular those exposed frequently to laser source. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cr3+ doped La 2 (WO 4) 3 nanoparticles are synthesized by soft chemical method. • The optical limiting properties of La 2 (WO 4) 3 nanostructures using CW laser at 785 nm was reported for the first time. • All sample possess RSA which is caused by two-photon absorption. • The presence of polarizable Cr3+ ions, results enhanced OL behaviour for 0.7 % Cr3+ doped La 2 (WO 4) 3 nanoparticles. In this article, we discuss the nonlinear optical limiting characteristics of pure and Cr3+ doped La 2 (WO 4) 3 nanoparticles using soft chemical method. We studied the third-order nonlinear optical properties of nanoparticle using a continuous-wave (CW) laser system pumped by a diode laser at 785 nm. The results reveal that the materials possess reverse saturable absorption (RSA) and self-defocusing in nature. Due to the presence of near-resonant excitation state, the material exhibits sequential two-photon absorption (excited state induced thermally) process. We observe a higher non-linear absorption coefficient (β) and nonlinear refractive index (n 2) for 0.7 % Cr3+ doped La 2 (WO 4) 3 systems which is higher than that of pure La 2 (WO 4) 3 nanoparticles. The transmittance decreases with increased input fluence for both pure and Cr3+ doped La 2 (WO 4) 3 samples exposing the optical limiting behavior of the prepared sample. The presence of larger concentrations of more polarizable Cr3+ ions, increased density of states, and higher oxygen defects resulted in enhanced OL behaviour for 0.7 % Cr3+ doped La 2 (WO 4) 3 sample. It is found that two photon absorption (β) is increased from 0.41 to 1.16 × 10-3 and third order nonlinear susceptibility (χ(3)) enhances from 3.909 x10-6 to 6.696 × 10-6 esu on Cr doping. The optical limiting threshold of pure and Cr x La 1-x WO 4 nanoparticles was also studied and found to be in the range of 91.2 to 86.2 W/cm2. As a consequence of the obtained results Cr3+ doped La 2 (WO 4) 3 is likely to be an appropriate candidate for CW low-power optical limiting (OL) applications. [ABSTRACT FROM AUTHOR]

• Intersubband transition in CdTe/ZnTe core/shell prolate spheroidal quntum dots. • Third-order nonlinear optical susceptibility. • The Third-nonlinear optical susceptibility shifts with the variation of core, the average shell thickness and eccentricity. In this paper, we have reported a more realistic model simulating the electronic and nonlinear optical properties in CdTe/ZnTe core/shell materials and inverted structure. In this model, we assume a prolate spheroidal shape for the considered nanostructure. The electronic band structure and the set of the wave functions were calculated by solving the Schrödinger Equation in the frame of the Effective Mass Approximation EMA and taking in consideration the Compact Density Matrix. The effects of the size and the eccentricity e on the third-order nonlinear optical susceptibility χ 3 are investigated. It was found that χ 3 is strongly affected by the size of core /shell prolate spheroid quantum dots (CSPSQDs) and the eccentricity e. Indeed, a spectacular red shift of peaks of χ 3 was conspicuous in addition to their intensification. [ABSTRACT FROM AUTHOR]

A transparent Rubidium hydrogen oxalate dihydrate (RbHOH) single crystal was synthesized by adopting the slow solvent evaporation method. RbHOH crystallizes in the triclinic structure with the P 1 ‾ space group. The characteristic FTIR spectrum reflects the vibrational modes of water molecules and hydroxyl groups available in the material. From the absorption spectrum, the lower cutoff wavelength of RbHOH was at 260 nm with an energy gap of 4.74 eV. From TG/DSC, the thermal stability of RbHOH is around 91 °C. The normal indentation size effect of the material was verified with the help of Vickers microhardness analysis.Dielectric measurement has been performed over a wide range of temperature, as a function of frequencies. The third-order nonlinear susceptibility of RbHOH was calculated as 3.95242 × 10−6 esu. [Display omitted] • The grown RbHOH single-crystal crystallized in triclinic structure with P 1 ‾ space group. • The material has a lower cutoff wavelength of 260 nm with an optical bandgap of 4.74 eV. • The material exhibits the normal indentation size effect and belongs to the soft material category. • The negative nonlinearity causes the self-defocusing effect in RbHOH single crystal. [ABSTRACT FROM AUTHOR]