Narrow Results

In the sight of the present demand of scientific exploration in nonlinear optics (NLO), we synthesized a symmetric donor–$\pi$–acceptor–$\pi$–donor (D–$\pi$–A–$\pi$–D) type organic chromophore [2-[2,6-di((E)-styryl)]-4H-pyran-4-ylidene]malononitrile (M1) for linear and nonlinear optical studies. The structural character of the compound M1 was confirmed using ¹H NMR, ${}^{13}$C NMR, and IR spectroscopy. The intramolecular charge transfer (ICT) in molecule M1 has been analyzed using absorption and fluorescence spectrometry in different nonpolar and polar solvents. The optical bandgap, optical conductivity, and linear refractive index of M1 were also calculated using UV–Vis absorption spectrum in CHCl₃. The thermogravimetric analysis (TGA) was also carried out to check the thermal stability of the compound M1 and it was found to be thermally stable up to 200^∘C. Furthermore, the third-order optical nonlinearity in M1 has been investigated elaborately using the $Z$-scan technique with a continuous wave (CW) diode laser at 520nm. The nonlinear absorption ($\beta$), nonlinear refraction ($n_2$), and nonlinear optical susceptibility (${\chi }^{(3)}$) were computed for various solution concentrations as well as several laser powers and the magnitude of all the parameters were found to vary linearly with concentration and power. The magnitude of two-photon absorption cross-section (${\sigma }_{\mathrm{\text{TPA}}}$) was also calculated and found to be of the order of 10${}^{10}$ GM. The optical limiting performance of the compound was also studied in different solution concentrations using the same laser. Furthermore, DFT and TD-DFT theoretical calculations were performed for the support of experimental results.

Nanoparticle Lead sulfide was synthesized via simple chemical method and deposited on glass substrates at different substrate temperatures by thermal evaporation technique. The synthesized nanoparticle PbS was analyzed and confirmed by X-ray diffraction (XRD), Scanning electron microscopy SEM with EDX and thermogravimetry. The structural, optical, morphological and electrical properties of the deposited films were studied using XRD, UV-Vis, Raman, SEM with EDX, atomicforce microscopy AFM and Hall Effect measurements. The thickness of the deposited samples was measured using thickness profilometer. The Raman shift in the peak occurs toward lower energy with increasing substrate temperature deposited lead sulfide. The Z-scan study with open aperture was carried out at 532 nm using 5 ns laser pulse on the deposited films which shows that nonlinear absorption arises from saturable absorption process. The deposited PbS film exhibits p-type conductivity in Hall measurement.

Optical limiting properties of 2,6-dibromo-3,5-distyrylBODIPY dyes were investigated by using the z-scan technique at 532 nm in the nanosecond pulse range. A strong reverse saturable absorption response was observed even in solution, which suggests that compounds of this type are potentially suitable for use in optical limiting applications.

The synthesis and characterization of a series of 3,5-di-$p$-benzyloxystyrylBODIPY dyes with different substituents at the meso-aryl position is reported. The photophysical and nonlinear optical properties are described. BODIPYs of this type are found to be suitable for optical limiting at 532 nm on the nanosecond timescale. An enhancement of the population of the T${}_{\mathrm{\text{1}}}$ state through the incorporation of bromine atoms at the 2,6-positions does not result in an enhancement of the optical limiting properties on a nanosecond timescale. This suggests that, in contrast with phthalocyanines, access to excited state absorption (ESA) from the T${}_{\mathrm{\text{1}}}$ state through the introduction of a heavy atom effect does not provide a significantly improved reverse saturable absorbance response compared to ESA from the S${}_{\mathrm{\text{1}}}$ state.

The results of recent studies on the optical limiting properties of BODIPY dyes at 532 and 1064 nm are described and compared. The optical limiting properties of novel 1,7-dimethyl-3,5-di-4-dihydroxyborylstyryl- and 3,5,7-tristyryl-1-methyl-BODIPY dyes were studied in CH₂Cl₂ and C₆H₆ and polystyrene thin films using the open aperture Z-scan technique at 532 nm with nanosecond laser pulses to provide an example of how the effective nonlinear absorption coefficient, the third order susceptibility, hyperpolarizability and limiting thresholds can be calculated.

Third-order nonlinear optical property of multiferroic bismuth ferrite (BiFeO₃) nanoparticles sintered at different temperatures has been studied by employing Z-Scan technique. BiFeO₃ (BFO) nanoparticles (NPs) were synthesized by the sol–gel process with different sintering temperature of 823K, 923K and 1023K. XRD reveals that all samples have single-phase rhombohedral structure with R3c space group with no secondary phases present. The calculated crystallite size for samples sintered at 823K, 923K and 1023K is found to be 75nm, 87nm and 94nm, respectively. Crystal structure parameters and phase analysis of the BFO samples are obtained by the Rietveld refinement (FullProf) method. FTIR spectra show the absorbance peaks at 448cm${}^{-1}$ and 533cm${}^{-1}$ which confirm the synthesis of NPs. SEM images show the agglomerated spherical particles. Average crystallite and particle size of the samples are found to increase by increasing the sintering temperature. EDX verifies the constituent elements and reveals that stoichiometry in sample preparation is well-matched with the atomic ratio of the experimental quantity. The nonlinear absorption coefficient is characterized by the Z-Scan method employing continuous wave (CW) laser operating at 532nm wavelength. Nonlinear absorption coefficient ($\beta$), evaluated by open aperture Z-scan data, is found to decrease with an increase in the particle size of the BFO NPs. BFO nanoparticles synthesized by optimizing the synthesis temperature can be used for the various applications of futuristic multiferroic and optical devices.

Two major reasons limit porphyrins photonic applications: (i) the difficulty of handling them in liquid solutions and (ii) their degradation with long exposure to light. This necessitates the use of appropriate solid matrices to host the porphyrin compounds such as Nafion (117), a stable and inert ion exchange polymer. The first part of this publication confirms such a possibility. In addition to their effective NLO properties, an enhancement of the Soret and Q-bands' absorbance width have been observed by blending three different porphyrin molecules in the Nafion column matrix membrane. This is an important development towards achieving efficient photon-harvesting medium for possible application in photonic devices. The second part of this contribution reports on the self-assembly/molecular recognition of a specific class of porphyrins giving rise to tubular nano-systems with potential THG nonlinear properties.

The optical limiting properties of three meso-pentafluorophenylstyrylBODIPY dyes are investigated in the presence and absence of methyl groups at the 1,7-positions that hinder free rotation of the meso-aryl group. Pentafluorophenyl groups are introduced at the meso-position, while 4-diethylaminostyryl groups are introduced at the 3- and/or 5-positions to form dyes with strong donor-$\pi$-acceptor (D-$\pi$-A) properties to enhance the dipole moment of the molecule. Favorable optical limiting properties are obtained for all three dyes, with the highest second-order hyperpolarizability value obtained for a monostyryl dye with no methyl groups at the 1,7-position. Bromination at the 2,6-positions of a 1,7-methyl substituted dye is found to result in second-order hyperpolarizability that is an order of magnitude lower than that calculated for the analogous non-halogenated dye.

Nanoparticles of Titanium dioxide $({\mathrm{\text{TiO}}}_2)$ with its unique optical and electronic characteristics is an important material for photochemical catalysis. The efficiency of catalytic activity of ${\mathrm{\text{TiO}}}_2$ anatase nanostructures is greatly influenced by the photo-generated bound excitons. It is found that the interaction of bound excitons generated in ${\mathrm{\text{TiO}}}_2$ enhances the cubic nonlinearity of the system due to strong oscillation of photo-generated bound excitons. The trapped electron hole pair concentration is directly proportional to the photocatalytic efficiency of the ${\mathrm{\text{TiO}}}_2$ anatase nanostructures. In our report, we show how these photo-generated bound excitons play a significant role in origin of third-order optical nonlinearities. In particular, we have measured large phase shift and seen two photon absorption process through closed and open aperture Z-scan, respectively, using femtosecond pulses at 532nm.

The copper oxide nanoparticles (CuO NPs) were synthesized via solution combustion approach with Bengal gram powder as a fuel. The XRD analysis confirms the monoclinic structure of CuO NPs. FT-IR spectrum reveals the formation of CuO NPs. SEM studies show that the NPs are nearly spherical, and the elemental composition was confirmed by EDAX. The absorption spectra revealed a direct optical band gap of 1.50eV. DFT calculations were performed to determine the HOMO–LUMO energy bandgap and found to be 1.72eV, which is in good agreement with the experimental value. The Z-scan technique was used to investigate the third-order nonlinear optical (NLO) characteristics using DPSS continuous wave laser (532nm, 200mW). A high reverse saturation absorption and negative nonlinear refractions were observed. Third-order NLO parameters $\beta$, $n_2$ and ${\chi }^{(3)}$ were found to be $19.6\times 10^{-5}$cm/W, $-1.12\times 10^{-8}$cm²/W and $5.97\times 10^{-7}$esu, respectively. The CuO NPs also displayed strong optical limiting behavior with a limiting threshold of 2.11kW/cm².

The synthesis and characterization of a novel dibrominated 1,3,5-tristyrylBODIPY dye is reported, and its potential utility as a singlet oxygen photosensitizer and optical limiting material is assessed. The main spectral band lies in the therapeutic window, and there is a moderately high singlet oxygen quantum yield making the dye potentially suitable for use in biomedical applications and as an optical limiting dye at 532 nm. The optical limiting parameters are comparable to those reported previously for 3,5-distyrylBODIPYs, which suggests that mixtures of 3,5-distyryl and 1,3,5-tristyryl compounds that are formed in Knoevenagel condensation reactions could be used for this application. Theoretical calculations are used to assess the effect of 1,3,5-tristyryl substitution. A smaller red shift of the main spectral band is observed upon styrylation at the 1-position than is the case with the 3,5-positions due to there being smaller MO coefficients at this position, limiting the utility of this structural modification method for shifting the main BODIPY spectral band further into the therapeutic window.

An experimental work has been done to measure the nonlinear refractive index of poly(2,5-dimethylaniline) (PDMA). In this work, a continuous wave (cw) Ar-ion laser has been used to calculate n₂ for a novel polymer; poly(2,5-dimethylaniline): synthesized from 2,5 dimethylaniline. The single beam Z-scan technique was used with laser beams of 514 and 488 nm wavelengths, taking PDMA in methanol solvent at different concentrations. The order of n₂ was found to be of the order of ~ 10^-14 esu.

Azo dyes with different pull/push substituents are selected as photosensitive molecules. Guest–host amorphous azo polymer samples are prepared by doping these azo dyes directly in poly(methyl methacrylate) polymeric matrices. Nonlinear optical properties of these pull/push type azo dye-doped polymers are investigated using the Z-scan experiment. The influence of the pull/push substituents and the azo dye concentration on the nonlinear optical property is studied.

In this work, the Au@Ag bimetallic core–shell nanostructures were synthesized by a seed-mediated growth. The crystal structure, morphology, elemental composition, atomic concentration, and absorption spectrum of the as-synthesized nanoparticles were characterized by means of X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible linear absorption spectrum, respectively. The femtosecond third-order optical nonlinearities of nanoparticle dispersions were investigated by carrying out the femtosecond-pulsed $Z$-scan measurements at 800nm. The experimental results indicate that Au@Ag core–shell nanoparticles exhibit the positive refractive nonlinearity and negative absorptive nonlinearity. The third-order nonlinear refraction indexes of Au and Au@Ag nanoparticles are measured to be $2.50\times 10^{-7}$ and $6.39\times 10^{-7}$cm²/GW, respectively. The results show that the bimetallic nanoparticle has potential possibility in nonlinear photonic applications.

The new prepared hybrid salt 1,1’-(Ethylene-1,2-diyl)dipyridinium pentacyanidonitrosoferrate(II) pentahydrate was synthesized. Then, it was characterized using different spectroscopic methods. The nonlinear optical properties of the new compound were investigated using the simple $z$-scan technique with a CW diode laser radiation ($\lambda =532$nm). Also, the $z$-scan technique with pump/probe configuration was utilized to observe the Cross Phase Modulation (XPM) phenomena. Theoretical fit to the new experimental data was performed to calculate the third order nonlinear optical parameters including the nonlinear refractive index, which is about $-5.90\times 10^{-7}$cm²/W. This kind of molecule is considered to be promising candidate for using in future optoelectronic devices.

The slow evaporation solution growth technique (SEST) was used to successfully grow inorganic single crystals of sodium sulphamate (NaS) in ambient conditions. The titled crystal’s structural and optical characteristics were evaluated using a variety of spectroscopic techniques. Powder X-ray diffraction (PXRD) analysis and Fourier transform infrared (FT-IR) spectroscopy were used to examine the crystal structure characteristics. Using UV-Vis spectroscopy, the optical properties of the NaS crystal were carefully examined, and the optical bandgap was determined using Tauc’s plot. The HR-XRD analysis examined crystalline perfection. Additionally, photoluminescence spectroscopy determined the emission spectra, and time-resolved photoluminescence measured the decay rate. The $Z$-scan technique was also used to examine the titled crystal’s nonlinear optical (NLO) performance.

The optical limiting properties of crown-ether-substituted scandium(III) phthalocyaninate complexes, bis-tetra-15-crown-5-phthalocyaninates Sc[(15C5)₄Pc]${}_2^{•0}$ (I) and Sc[(15C5)₄Pc]${}_2^{-}$ (Ia), together with monophthalocyaninate [(15C5)₄Pc]Sc(OAc) (II) were measured by using the Z-scan technique (532 nm laser and pulse rate of 10 ns). It was revealed that expansion of the $\pi$-system on moving from the monomeric Sc complex II to sandwich compound I and changing the electronic state of the sandwich compound from the anionic Ia species to the neutral radical I improves the optical limiting properties. The Im[${\chi }^{(3)}$] values obtained lie in the 10${}^{-12}$–10${}^{-10}$ esu range that is consistent with those reported previously for other organic chromophores. The crystal structure of sandwich Sc(III) complex I was elucidated by means of single-crystal X-ray diffraction analysis and was used to guide a series of theoretical calculations. It was demonstrated that the application of simplified time-dependent density functional theory (sTD-DFT) calculations can provide reasonably accurate predictions for compounds of this type when the geometries of the complexes are clearly defined.

The optical limiting properties of three meso-pyridyl-distyrylBODIPY dyes with differing alkyl substitution patterns at the 2,6- and 1,7-positions on the pyrrole moieties are investigated. Styryl groups are introduced at the 3,5-positions to form dyes with strong donor-$\pi$-acceptor (D-$\pi$-A) properties. Favorable optical limiting properties are obtained for all three dyes, with the highest second-order hyperpolarizability obtained for a dye that is unsubstituted at both the 2,6- and 1,7-positions suggesting that the optical limiting properties are enhanced when the meso-aryl ring can freely rotate into the plane of the BODIPY core.

Third-order nonlinear optical properties of tetra-phenyl porphyrin (H${}_{\mathrm{\text{2}}}$TPP) derivatives viz., H${}_{\mathrm{\text{2}}}$TPP(OH)${}_{\mathrm{\text{4}}}$ and Zn(II)TPP doped in boric acid glass thin films were measured using single beam Z-scan and forward degenerate four-wave mixing (DFWM) techniques. Excited state lifetimes and absorption cross-sections were estimated from these experiments. Thickness of the porphyrin doped sandwich glass films were determined using DFWM technique for the first time. The values of nonlinear refractive index ($n_2$) obtained for these systems are are found to be sensitive to the nature of substituents in porphyrin molecule. These results are interpreted in terms of delocalized $\pi$ electrons contributing to the third-order optical nonlinearity.

Selenium nanoparticles were fabricated using a physical deposition method based on heterogeneous condensation. The Selenium nanoparticles were deposited on a quartz substrate and the ultrafast nonlinear optical responses were investigated by using the $Z$-scan technique. The nanosize films showed two-photon absorption and a large positive nonlinear refractive index at 800 nm excitation wavelength. The obtained real and imaginary parts of the intensity-dependent complex third-order nonlinear susceptibility of the Selenium nanoparticles ranged from $10^{-11}$ to $10^{-8}$ (esu) for different irradiance levels.