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This work aims to discuss the impact of the interaction of a high-power laser with the SrWO₄/MoS₂ nanocomposites synthesized by the solvothermal method. The effect of different concentrations of MoS₂ on the structural, morphological, optical and nonlinear optical (NLO) characteristics of SrWO₄ nanostructures was studied by utilizing XRD, Raman, FTIR, SEM, TEM, UV–Visible absorption and Open aperture Z-scan technique using Nd: YAG pulsed laser. The composites mitigate the successful interaction of MoS₂ in the SrWO₄ lattice through standard phase confirmation, change in lattice parameters and induced strain from XRD analysis. The mixed morphology shows the blended nature of composites through HRTEM and SEM. The functional and vibrational modes of nanocomposites were explored by FTIR and Raman spectroscopic techniques. The photoluminescence spectroscopy analyzed the influence of defect states. The optical parameters like absorption edge, band gap energy and Urbach energy were calculated by linear optical studies. Z-scan studies show the reverse saturable nature of all samples with more absorption and less transmittance at the focus. The experiment was extended to the analysis of the optical limiting (OL) behavior studies to understand their potential application in laser safety devices. The higher concentration of MoS₂ in the strontium matrix yields a higher nonlinear absorption coefficient of $1.531\times 10^{-10}$m/W and a lower optical threshold of $0.61\times 10^{11}$W/m². The inclusion of 20% MoS₂ in SrWO₄ significantly enhances the nonlinear absorption and the optical limiting ability which can be the best choice of NLO material for future optoelectronics.

This paper presents a theoretical model for an arbitrary $n$-order nonlinear refraction using an elliptical Gaussian beam propagating in a thin nonlinear medium. In contrast to circular Gaussian beams, elliptical Gaussian beams better represent real laser beams and distortions. The model derives an analytical expression for the optical normalized transmittance in $Z$-scan experiments. This is achieved by using the Gaussian decomposition method and weak phase approximation. The transmittance depends on the on-axis nonlinear phase shift, elliptical beam sizes along transverse axes, and the nonlinear refractive index. Fitting the expression to $Z$-scan data extracts these parameters.

A hybrid luminescent-magnetic nanostructure based on graphene oxide, magnesium ferrite, and CdTe quantum dots (QDs) was synthesized (GO@MgFe₂O₄–TMSP–CdTe nanocomposite). The surface of the GO was coated with ferrite nanoparticles using a co-precipitation method. Subsequently, the nanocomposite was linked to CdTe QDs using a TMSP ligand. The structural, optical, and magnetic properties of the nanostructure were investigated. Moreover, the real and imaginary components of the refractive index and dielectric function were assessed using the Kramers–Kronig method based on FTIR spectroscopy across the 500–4000cm${}^{-1}$ spectral range. As a result, the transversal optical and longitudinal optical phonon modes were identified at 436cm${}^{-1}$ and 600cm${}^{-1}$, respectively. Furthermore, this study utilized the Z-scan technique to investigate the nonlinear thermo-optical responses of the prepared sample. The sample’s nonlinear behavior was examined at various laser intensities, revealing significant nonlinear thermo-optical responses in the visible spectrum. The nonlinear absorption coefficient is a result of the two-photon absorption effect, while the nonlinear refractive indices indicate the self-defocusing effect, under varying laser powers. Moreover, the assessment of the figure of merit indicates the potential for the use of this sample in optical switches, based on the experimental results.

A well-aligned single-crystalline barium titanate (BaTiO₃) nanostructured layer was prepared by the growth and conversion of vertically aligned TiO₂ nanorods. This was achieved through a two-step hydrothermal method on fluorine-doped tin oxide (FTO)-coated glass substrates via the dissolution-nucleation-recrystallization mechanism. The morphology, crystal structure and optical properties were investigated using field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), Raman spectroscopy, photoluminescence (PL) and Z-scan techniques. The X-ray and selected area diffraction patterns (SAED) confirmed the formation of the aligned single-crystalline tetragonal BaTiO₃ layer. The room temperature Raman spectrum showed the tetragonal TiO₂-related vibrational modes in BaTiO₃. The PL spectra indicated the coalescence of band edge emissions of BaTiO₃ and TiO₂ in the blue and visible regions of the investigated spectra. The Z-scan experiments performed using the CW Nd:YAG laser revealed a positive nonlinear refractive index on the order of 10${}^{-7}$ cm²W${}^{-1}$, indicating the self-focusing type of cation in the BaTiO₃ sample. The nonlinear absorption coefficient of the BaTiO₃ nanostructures in the order of 10${}^{-7}$ cm W${}^{-1}$ was also calculated. As expected, the BaTiO₃ nanostructure synthesized in this study is a good candidate for use in nonlinear optics.

The slow solvent evaporation technique was employed to grow pure and Brilliant Green (BG) dye-doped bis-thiourea cadmium acetate (BTCA) crystals. This study explores, for the first time, the use of BG dye as a dopant to tailor the optical properties of BTCA crystals. By influencing both linear and third-order nonlinear optical responses, BG doping holds promise for applications in integrated optic devices. The UV-Visible spectrum analysis between 200nm and 1,000nm has been carried out to ascertain the generated crystals optical transparency. The 632.8nm Z-scan measurements with both open and closed apertures were employed to characterize the type of third-order nonlinearity exhibited by the grown crystals and calculated successfully. These properties include the nonlinear refractive index ($n_2$), nonlinear absorption coefficient ($\beta$), and third-order nonlinear optical (TONLO) susceptibility (${\chi }^3)$. Calculated values of the ${\chi }^3$ of pure BTCA and BGDBTCA crystal are found to be $2.448\times 10^{-6}$ and $3.658\times 10^{-6}$esu, respectively.

In this study, natural crystalline material collected from the head of the Pomadasys maculatus fishes are characterized for their potential applications in various fields including laser optics. Interestingly, the natural otolith crystals exhibit two-photon absorption-induced optical limiting characteristics under Nd:YAG laser excitation. The optical limiting threshold for otolith crystals was found to be $6.22\times 10^{12}$W/m². The presence of Calcium (Ca), Copper (Cu), Potassium (K), and Sodium (Na) is confirmed by ICP-OES analysis. The presence of Ca is primarily from the functional group of otolith that was found on the surface of otolith. From the GCMS analysis, 25 compounds were found in the methanol extract of otolith. The magnetic property of Pomadasys maculatus fish sample was analyzed by vibrating sample magnetometer (VSM). The decomposition/mass loss over a temperature was analyzed by thermogravimetric analysis (TGA) and also the endo and exothermic event temperatures and phase transitions were observed from Differential Thermal Analysis (DTA).

The optical limiting properties of a 1,7-dithien-3-yl-3,5-di-4-hydroxyphenyl-azaBODIPY dye and its silver nanoparticle (AgNP) conjugate on the nanosecond timescale at 532 nm are reported. The photophysicochemical properties are compared to those of the parent 1,3,5,7-tetraphenylazaBODIPY complex. The thien-3-yl rings at the distal positions facilitate conjugation to AgNPs through the Ag-S interaction and a significant red shift of the main azaBODIPY spectral band. Favorable optical limiting properties are obtained that suggest 1,3,5,7-tetraarylazaBODIPYs and their nanoparticle conjugates merit further in-depth study in this context. This is further enhanced by conjugation to AgNPs.

The valence electronic properties of some unsubstituted and peripherally substituted oxo-titanium phthalocyanines are reported. Semiempirical quantum chemical calculations show that the nature of peripheral substituents has a strong bearing on the valence electronic properties, including the state dipole moments and absorption wavelength. The non-linear optical response was measured around the the Q-band resonance. The effect of different substituents and substitution patterns on the non-linear behaviour of the samples was determined. The combined results suggest that tuning of electronic and optical properties is effectively achieved by functionalization of the edges of the conjugated ring.

Deposition of zinc sulfide (ZnS) thin films on Si (1 0 0) and glass substrates has been performed using RF magnetron sputtering method. Film structure has been analyzed by X-ray Diffraction (XRD), while the scanning electron microscope (SEM) images have been used to explore the film morphology. FTIR and Raman spectroscopies have been used to confirm the film composition. The stoichiometry has been verified by Energy dispersive X-ray spectroscopy (EDX) technique. The XRD patterns have indicated that the films possess a polycrystalline nanocrystallite cubic structure. The optical properties of the grown films were characterized by optical transmittance measurements (UV–Vis). The deduced energy bandgaps of the films show an increase from 3.75 eV to 3.88 eV with the power source changes from 90 W to 125 W. Furthermore, Z-scan technique (CW diode laser $\lambda =635$ nm) was employed to estimate the nonlinear optical absorption of the prepared ZnS films.

The structural dependence of nonlinear optical properties associated with ADP-doped PVA/PVP polymer composites is discussed in this work. Polymer composites are fabricated using the solution casting method. X-ray diffraction (XRD) was used to perform structural analysis on these samples whose average crystallite size increases with an increase in dopant concentration. Results from UV–Vis–NIR spectra show that the samples are transparent in the IR region. The Z-scan technique was established by following the method described by Sheik-Bahae et al. The shape of the open aperture plot suggests that the samples exhibit two-photon absorption. The NLO properties such as nonlinear absorption coefficient ($\beta )$, two-photon absorption cross-section (${\sigma }_2)$ and the imaginary part of third-order nonlinear susceptibility $({\chi }^{(3)})$ were investigated at 1064 nm and these values were found to be in the order of $\sim {10}^{-7}$W/cm, $\sim {10}^{-20}$cm⁴/GW and $\sim {10}^{-14}$esu, respectively. The open aperture Z-scan method yielded optical limiting data, from which the optical limiting threshold was calculated to be in the order of $\sim {10}^{13}$W/m². Functional data analysis uses a suitable basis representation to assess the functional correlation between global and local variables.

Investigation of nonlinear absorption coefficient of eosin blue dye based side chain poly(methacrylate) films is presented using diode pumped Nd:YAG laser radiation (λ=532 nm) and the Z-scan technique. The effect of the concentration in polymer film and the increase in the number of methylene spacers, hooked to the eosin blue dye, on the nonlinear absorption coefficient is also discussed. It is shown that the nonlinear absorption coefficient in samples is due to the two-photon absorption effect. Moreover, the optical limiting characteristics of polymers film are explored.

The third-order optical nonlinear properties of CdSe quantum dots (QDs) and CdSe-C₆₀ QDs are investigated by Z-scan technique with picosecond pulses at the wavelength of 800 nm. The value of the nonlinear absorption coefficient β of CdSe-C₆₀ QDs is measured to be 2.9 cm/GW, which is about two times larger than that of CdSe QDs. The nonlinear refraction index γ of CdSe-C₆₀ QDs is -2.8 × 10^-3cm²/GW, which is about seven times larger than that of CdSe QDs. Presence of C₆₀ contributes to the larger optical nonlinearity of CdSe-C₆₀ QDs comparing with CdSe QDs.

The optical nonlinear absorption properties in sputtering Indium nitride (InN) film were investigated under the excitations of nanosecond, picosecond and femtosecond pulsed lasers by open-aperture transmission Z-scan technique (TZ-scan). Under the condition of hν > E_g, the saturable absorption (SA) phenomena induced by one-photon transition were observed in both nanosecond and picosencond pulsed TZ-scan measurements. When 2hν > E_g > hν, the film presented SA due to the two-photon transition under the excitation of picosecond laser. However, at femtosecond 800 nm, the film showed the two-photon absorption (TPA) instead of SA, and the TPA coefficient tended to a saturable value as the excitation intensity increased. The results indicate that the InN film is a kind of good saturable absorber.

3-hydroxyflavone (3-HF) is an organic molecule with excited-state intramolecular proton transfer (ESIPT) effect. The nonlinear optical properties of 3-HF in the three different polar solvents (cyclohexane, ethanol and their mixture) were investigated by Z-scan technique under the excitation of the 1064 nm picoseconds laser pulse. The 3-HFs in these solvents exhibit the self-defocusing effect and their nonlinear refraction indices are in the order of $10^{-19}{\mathrm{\text{m}}}^2/\mathrm{\text{W}}$$(10^{-12}\mathrm{\text{esu}})$. The large nonlinear refraction indices may allow them to be widely used for the optoelectronic devices.

Thioglycolic acid capped cadmium selenide (CdSe) and CdSe@ZnO core–shell quantum dots have been synthesized in aqueous phase. The sample was characterized by UV-vis spectrophotometer, TEM and Z-scan technique. The nonlinear optical parameters viz. nonlinear absorption coefficient $(\beta )$, nonlinear refractive index $(n_2)$ and third-order nonlinear susceptibilities $({\chi }^3)$ of quantum dots have been estimated using second harmonic of Nd:YAG laser. The study predicts that CdSe@ZnO quantum dots exhibits strong nonlinearity as compared to core CdSe quantum dots. The nonlinearity in quantum dots is attributed to the presence of resonant excitation and free optical processes. The presence of RSA in these nanoparticles makes them a potential material for the development of optical limiter.

For the nonlinear materials, not only the ratio ρ of the imaginary to the real part of the third-order nonlinear susceptibility but also the finite aperture size S exert a great influence upon the appearance of a peak on the Z-scan transmittance curve. This article investigates the ρ dependence of the critical aperture size S^c, which determines whether a transmittance peak occurs or not, and the dependence of the critical value ρ^c on the parameter S for the thin-sample and low irradiance limits with a Gaussian beam. These results may be applied to the adjustment of experimental conditions at all times and the assessment of the correctness of data analysis. The experiment with CS₂ seeking the critical value S^c has verified above results.

We suggest an accurate method for extracting nonlinear refraction from the closed aperture Z-scan transmittance curve with the aid of the open aperture Z-scan transmittance curve; this method possesses very high accuracy, especially, in the presence of nonlinear absorption and/or for the larger linear transmittance of the aperture. The relative error of the results given by our method is only weakly dependent on the intensity of the incident light; which is a significant advantage over other methods. This method is also demonstrated experimentally on a solution of Ni(mpo)₂ complex.

The nonlinear optical properties of heterocyclic compounds (1-7) were investigated. π-Centers benzo[1,2-b:4,3-b']dithiophene (1) and trithia[5]helicene (5) were studied. Compounds 2-4, 6 and 7 possess either donor-π (D-π) or donor-π-acceptor (D-π-A) structures. The optimized geometry of 7 shows a 3D helical structure. Two-photon absorption cross-sections related to the third-order nonlinear susceptibility were measured using open-aperture Z-scan techniques. Compound 7 has a two-photon absorption cross-section of 103 GM when excited at 720 nm. Important molecular structure-nonlinear optical property relationships are formulated.

The nonlinear refraction in the single- and double-sided 40-bilayer TMAF/PSS electrostatic self-assembly films were measured by closed-aperture Z-scan technique with picosecond laser pulses (with duration of 40 ps at 532 nm). The materials contain a positively charged material trifluoroacetic acid (TFA) salt of amino-substitute methanofullerene derivative monoadduct fullerene (TMAF) and a negatively charged material ploy (sodium 4-styrenesulfon ate) (PSS). The experimental results show that under the conditions of the peak intensity I₀ = 7.0 GW/cm², both the single- and double-sided films demonstrate third- and fifth-order non-linearities, and the fifth-order non-linearity has greater contribution to the nonlinear refraction than the third-order nonlinearity. The theoretical fittings also prove that the nonlinear refraction coefficients both γ and η are almost the same for the same materials no matter what the measurements are from the single- or the double-sided films.

A highly-conjugated polar dye with three aromatic rings connected with azo groups was prepared and it was incorporated in polycinnamate. It showed a third-order nonlinear susceptibility of 8 × 10^-10esu determined by a Z-scan technique. The unpoled and poled films show the same susceptibility indicating the polymer film could not be poled. The open aperture Z-scan showed negligible two-photon absorption at 1064 nm.