Second-order Molecular Hyperpolarizability Research Articles

Diagrammatic theory of linear and nonlinear optics for composite systems

We present a general formalism to model and calculate linear and nonlinear optical processes in composite systems, based on a graphical representation of light-matter interactions by loop diagrams associated with Feynman rules. Through this formalism, we recover the usual second-order response of a simple system by drawing four times fewer loop diagrams than doubled-sided ones. For composite systems, we introduce coupling Hamiltonians between subsystems (for example, a molecule and a substrate), graphically represented by virtual bosons. In this way, we enumerate all the diagrams describing the second-order response of the system and show how to select those relevant for the calculation of the molecular second-order hyperpolarizabilities under the influence of the substrate, including effective second-order contributions from the molecular third-order response. As it applies to all nonlinear processes and an arbitrary number of interacting partners, this representation provides a general frame for the calculation of the nonlinear response of arbitrarily complex systems.

The significant role of molecular dipole arrangements on the second and third-order nonlinear optical properties of a furan based chalcone

In this article, we report an experimental investigation on second and third-order nonlinear optical (NLO) properties of an efficient chalcone material 1-(5-methyl furan-2-yl)-3-(4-nitrophenyl) prop-2-en-1-one (MFNP) along with other characterization techniques. The synthesized material is confirmed through FT-IR and FT-Raman spectroscopic techniques. Single-crystal XRD study showed that the crystal belongs to the triclinic crystal system crystallizing in the P1 space group which is a non-centrosymmetric crystal form. From UV-VIS-NIR spectroscopy, the crystals were found to possess less absorbent in the visible region. Furthermore, the crystal exhibits excellent thermal stability up to 136 °C. The intermolecular interactions in the crystal were identified by obtaining the Hirshfeld surface and the related 2D finger plots. The second harmonic generation (SHG) efficiency of MFNP is three times the standard KDP crystals. Using a continuous-wave laser beam z scan experiment was performed and the “nonlinear refractive index (n2)”, “third-order nonlinear absorption coefficient (β)” and “second-order molecular hyperpolarizability(γh)” were calculated for MFNP. The estimated threshold value for optical limiting was found to be 1.85 kJ/cm2. The excellent experimental results show that MFNP is a very useful material especially in the field of optical power limiting applications.

Fluorescence and Nonlinear Optical Properties of Alizarin Red S in Solvents and Droplet.

The enhancement of the nonlinear properties of materials is an interesting topic since it has many applications in optical devices and medicines. The Z-scan technique was used to study the values of the two-photon absorption (β), second-order molecular hyperpolarizability (γR), third-order susceptibility (χR), and nonlinear refractive index (n2) of Alizarin Red S in different media using a continuous-wave diode-pump laser radiation at 532nm. For Alizarin Red S in a droplet, the β, n2, χR, and γR were estimated at the order of 10-7cm2/W and 10-12cm/W, 10-3m3W-1s-1 and 10-24m6W-1s-1, respectively. The results indicated that the values of β and n2 reduced, whereas the values of χR and γR were enhanced when the solvent was changed from droplet to water, DMF, and dimethyl sulfoxide due to the change in the solvent's dielectric constant (ε). Moreover, the values of β were enhanced by an increase in the concentration of the surfactant in the aqueous solution. The absorption spectra of Alizarin Red S in the aqueous solution was observed at 428nm, and a few red shifts in the absorption spectra were observed with a reduction in the dielectric constant of the medium. The same effect was observed in the absorption spectra of Alizarin Red S in the droplet when the bulk dielectric constant reduced. The dielectric constant can affect the fluorescence spectra of Alizarin Red S when the solution is changed from water to dimethyl sulfoxide. The dipole moments of Alizarin Red S in the different media were studied using the quantum perturbation theory.

Third-order nonlinear optical properties and ultrafast excited-state dynamics of benzothiazolium salts: Transition in absorption and refraction under different time regimes

Two benzothiazolium salts of D-π-A structure, (E)-3-ethyl-2-(2-(pyren-1-yl) vinyl) benzo[d]thiazol-3-ium iodide (EPBI) and (E)-3-ethyl-2-(2-(9-ethyl-9H-carbazol-3-yl) vinyl) benzo[d]thiazol-3-ium iodide (ECBI) were synthesized and spectroscopically characterized. Z-scan measurements were performed at 532 nm with 190 femtosecond and 15 picosecond laser beam respectively. EPBI displays the efficient third-order nonlinear optical susceptibility χ(3) of 1.5 × 10−11 esu and molecular second-order hyperpolarizability γ of 2.8 × 10−29 esu which are one order larger than those of ECBI, and EPBI exhibits reverse saturable absorption and self-defocusing refraction while ECBI exhibits saturable absorption and self-focusing refraction in 15 ps time mechanisms. In 190 fs time mechanisms, both of them exhibits saturable absorption. Further dynamics analysis for these transition in different time regimes and determination of key parameters were performed via DFT calculation and transient absorption experiment.

Nonlinear optical properties of crocin: From bulk solvent to nano-confined droplet

Crocin has a strong Two-photon Absorption (TPA) capability that makes it suitable for medicine and photonic devices. To study the linear and nonlinear optical properties of crocin in solvent and Microemulsion (MEs), Z-scan instruments, Uv–Vis, and fluorescence were used. Nonlinear absorption coefficient (β), nonlinear refractive index (n2), third-order susceptibility (χR), and second-order molecular hyperpolarizability (γR) values were extracted from the Z-scan instrument. The β and n2 reduce with the increase in solvent's dielectric constant (ε). In crocin mixed with MEs, the nonlinear optical values depend on the size and concentration of the droplet at constant crocin concentration. The MEs can enhance the value of β as compared with other solvents. A red shift in absorption spectra of crocin was observed with an increase in ε. However, the absorption peak was constant in the MEs. The ratios of the excited state to the ground state of the dipole moments (μe/μg) of crocin in the solutions were determined by the quantum perturbation theory. It was shown that μe/μg has similar behavior with 1/γR. The value of μg and γR are reduced with an increase in ε.

Bulk crystal growth, spectral, optical, thermal, electrical and third-order NLO properties of benzylidene malononitrile derivative single crystal: a promising material for nonlinear optical device applications

Bulk organic intramolecular charge transfer nonlinear optical single crystal of 2-(2,4-dimethoxybenzylidene) malononitrile (DMM) with the sizes of 24 × 18 × 13 mm3 have been successfully grown by slow evaporation solution growth technique at 35 °C using acetone as the solvent. The lattice parameters of the grown DMM crystal was evaluated by single crystal X-ray diffraction analysis. The optical transmittance (T) data was taken from the well-polished crystal of DMM, and cut-off wavelength (λ = 483 nm) was identified by UV–Vis spectral studies. Thermal stability and melting point (145.78 °C) were studied with TGA–DSC analysis. The low value of the dielectric constant (er) of DMM suggests that the crystal can be used in the microelectronics industry. The laser-induced damage threshold experiment shows that the grown DMM bulk crystal possess an excellent resistance to laser radiation with a high threshold up to 1.75 GW/cm2, much larger than those of several known organic and inorganic NLO materials. The DMM crystal exhibits positive optical non-linearity and reverse saturation absorption. It also exhibited a nonlinear refractive index (n2) in the order of 10−11 m2/W, a nonlinear absorption coefficient (β) in the order of 10−5 m/W, third order non-linear susceptibility (χ(3)) in the order of 10−5 esu and a second-order molecular hyperpolarizability (γ) in the order of 10−33 esu. All the above results indicate that DMM has a potential application as a useful NLO candidate.

Polarization-Resolved Third-Harmonic Scattering in Liquids

Third-harmonic scattering (THS) is an unexplored third-order nonlinear optical process despite the fact that it is quite an easy technique to handle that quantifies the molecular second-order hyperpolarizability γ(−3ω;ω,ω,ω). In a liquid, light interaction is subject to isotropic averaging of the local symmetry (multipolar activity), and the mutual exclusion rules applies. While second-harmonic scattering (SHS) gives access to the dipolar and octupolar response of molecules, the even symmetry representations (isotropic, quadrupolar, and hexacadecapolar) are THS-active. This unique high level of molecular information can be achieved using THS polarization-resolved studies. Third-harmonic scattering, as second-harmonic scattering does but in a complementary way, constitutes a real breakthrough technique to study/monitor molecules, ionic species, nanomaterials, and bulk materials.

Synthesis, growth, structure and characterization of 1-Ethyl-2-(2-p-tolyl-vinyl)-pyridinium iodide (TASI) – An efficient material for third-order nonlinear optical applications

A new organic stilbazolium derivative, 1-Ethyl-2-(2-p-tolyl-vinyl)-pyridinium iodide (TASI), was grown from methanol:acetonitrile (1:3) mixed solvent by slow evaporation technique. Single crystal X-ray diffraction analysis revealed that TASI crystallizes in triclinic system with a centrosymmetric space group P-1. The molecular structure and the presence of expected functional groups of TASI were confirmed by 1H NMR and FT-IR spectroscopic studies. The HOMO and LUMO energies influence the charge transfer takes place within the molecule. The grown crystal was thermally stable up to 210 °C as determined by TG/DTA analysis. UV-Vis-NIR spectral study showed that the grown crystal was transparent in the wavelength range of 438–1100 nm. Mechanical behaviour and surface laser damage threshold were studied to find the suitability of the grown crystal for device fabrication. Studies of its third-order nonlinear optical properties using a Z-scan technique demonstrates that TASI crystal is capable of exhibiting reverse saturable absorption and self-focusing performance with the second-order molecular hyperpolarizability (γ) 4.983 × 10−34 esu. The third-order nonlinear susceptibility of TASI was found to be 8.931 × 10−6 esu, which is higher than a few other stilbazolium derivative crystals.

Study of Structure–Third-Order Susceptibility Relation of Indandione Derivatives

By using the Z-scan method we studied the third-order nonlinear optical parameters of several aminobenziliden-1,3-indandione (ABI) derivatives that have previously been shown to own second-order nonlinear optical properties. Measurements were carried out using two 1064 nm Nd:YAG lasers with picosecond (ps) and nanosecond (ns) pulse widths, respectively. When ns laser was employed in the Z-scan setup, a strong thermal lensing took place resulting in severe overestimation of optical Kerr coefficients. Due to this reason the ps laser was employed to evaluate correct magnitude of Kerr effect. For investigated organic molecules, experimental results show that two-photon absorption at 1064 nm is in correlation with molar extinction coefficient at 532 nm. Here we demonstrate good linear correlation between values of second-order molecular hyperpolarizability determined experimentally and those obtained by quantum chemical modeling.

Electrostatic self-assembled design strategy for tetracarboxylic Nickel(II) naphthalocyanine ultrathin film for high-performance nonlinear optical properties

The rational design and controllable preparation of the solid film with strong molecular coupled effect represents a long-standing challenge for developing advanced practical nonlinear optical (NLO) materials. Here, we report a general electrostatic self-assembled strategy toward fabricating tetracarboxylic Nickel(II) naphthalocyanine (NiNcC4) ultrathin film on solid substrate with an ordered molecular arrangement based on the controllable deposition of anionic NiNcC4 naphthalocyanine and cationic polydiallydimethyldiallylammonium chloride (PDDA). The 30-bilayer P/NiNcC4 film shows an ordered conformation of face-to-face molecular arrangement, ultrathin thickness (126.6 nm) and a Raman enhancement phenomenon, and exhibits a high second-order molecular hyperpolarizability γ of 7.0 × 10−27 esu, which is three orders larger than that of NiNcC4 aqueous solution, demonstrating the potential of strongly molecular coupling effects for advanced self-assembled systems.

Synthesis, Z-Scan and Degenerate Four Wave Mixing characterization of certain novel thiocoumarin derivatives for third order nonlinear optical applications

The third order nonlinear optical features of certain novel thiocoumarin derivatives have been studied. Single beam Z-scan study on these compounds reveals that the compounds exhibit self defocusing effect upon irradiation with 532 nm, 7 ns pulses of Nd:YAG laser. Nonlinear absorption coefficient, nonlinear refractive index and second-order molecular hyperpolarizability values were estimated. The optical power limiting properties of the compounds are found to be attributable to both two-photon and excited state absorption. Some of the samples show nonlinear absorption coefficient (βeff) as high as 24.5 cm/GW. UV–Visible and photoluminescence outputs of these compounds reveal remarkable absorptive and emissive properties. This article also reports extraordinary growth of third order optical nonlinearity in pure coumarin upon certain donor substitutions in lieu of hydrogen. Degenerate Four Wave Mixing (DFWM) signals of the compounds were analyzed to verify the Z-scan results. Electrostatic Surface Potential (ESP) mapping and structure optimization techniques have been employed to interpret the structure-property relationship of each molecule.

Solvatochromic effect on UV–vis absorption and fluorescence emission spectra, second- and third-order nonlinear optical properties of dicyanovinyl-substituted thienylpyrroles: DFT and TDDFT study

The nonlinear optical properties of dicyanovinyl-thienylpyrroles 1–6 compounds were investigated by the determining of the first-order molecular static hyperpolarizability (β) and the second-order molecular static hyperpolarizability (γ) in the ground state by using the HSEh1PBE/6-311G(d,p) level of density functional theory (DFT). The photophysical behavior of compounds 1 and 5 in polar and non-polar solvents was studied by using UV–vis absorption and fluorescence emission spectroscopies. In order to investigate the effects of these solvents, the time-dependent density functional theory (TD-DFT) calculations with the polarizable continuum model (PCM) in the excited state were performed. The UV–Vis absorption and fluorescence emission spectra for compound 5 were also simulated using TD-HSEh1PBE/6-311G(d,p) level, and the major contributions to the electronic transitions for compounds 1–6 were obtained. The β0 value (18.74×10−30esu) calculated by using HSEh1PBE/6-311G(d,p) for compound 2 is 1.49 times lower than the experimental value (28×10−30esu), and 2.34 times greater than pNA value (8×10−30esu). The β and γ parameters for compound 2 is lower than 1 and 3–6 due to electron donating pyrrole ring and electron accepting dicyanovinyl group. Moreover, we used the hybrid DFT methods (B3LYP, M062X, CAM-B3LYP and BHandHLYP) to show the accuracy for first static hyperpolarizability values for compounds 1–6. The β0 parameter for compound 5 in both polar and non-polar solvents was examined by using two level model.

Enhanced microscopic nonlinear optical properties of novel Y-type chromophores with dual electron donor groups

In this Letter, novel Y-type chromophores with dual electron donor groups, containing either styryl or azobenzene based π-conjugated bridge structures, were synthesized and their chemical structures, molecular configuration, microscopic optical properties as well as thermal properties were systematically characterized. The experimental results indicated that eight times increasing of second-order molecular hyperpolarizability as well as 50–100nm blue shift of maximum absorption band for azobenzene based chromophore were observed by introducing Y-type dual electron donor groups, which was derived from the highly efficient ‘total charge transfer’ in this kind of chromophore as confirmed by the density functional theory calculation.

Crystalline perfection, third-order nonlinear optical properties and optical limiting studies of 3, 4-Dimethoxy -4′-methoxychalcone single crystal

Transparent good quality single crystals of organic nonlinear optical material, 3, 4-Dimethoxy -4′-methoxychalcone (DMMC) were grown by slow evaporation solution growth technique in acetone at ambient temperature. The lattice parameters were estimated from powder X-ray diffraction. The crystalline perfection has been evaluated by high resolution X–ray diffractometry (HRXRD). The UV–vis-NIR absorption spectrum reveals that the crystal is transparent between 440nm and 900nm for optical applications. The fluorescence spectrum shows a peak at about 482nm and indicates that the crystal has a blue fluorescence emission. The third order nonlinear optical properties of solution of DMMC in N, N-Dimethylformamide (DMF) solvent has been investigated using Z-scan technique with femtosecond (fs) Ti:sapphire laser pulses at 800nm wavelength. The calculated values of nonlinear refractive index, nonlinear absorption coefficient, and the magnitude of third-order susceptibility are of the order of −7.7×10-14cm2/W, 1.7×10−9cm/W and 6.7×10−12e.s.u. respectively. The two photon absorption (2PA) cross section and molecular second-order hyperpolarizability values obtained is of the order of 10−49cm4s/photon/molecule and 2.8×10−31 e.s.u. respectively. The crystal shows optical-limiting (OL) effects for femtosecond laser pulses at 800nm. The results suggest that the nonlinear properties investigated for DMMC are comparable with some of the reported chalcone derivatives and can be desirable for nonlinear optical applications.

Z-scan study of third-order nonlinear optical properties of three dmit complexes

Three dmit2− complexes, [(C4H9)4N]2[Mn(dmit)2], [(C4H9)4N]2[Cu(dmit)2] and [(C3H7)4N] [Ni(dmit)2], abbreviated as BuMn, BuCu and PrNi, were synthesized. Their third-order nonlinear optical properties in acetonitrile were investigated using the laser Z-scan technique with 20ps pulses at 1064nm. The Z-scan spectra revealed that BuMn exhibited self-focusing effect and negligible nonlinear absorption, BuCu exhibited self-defocusing effect and two-photon absorption, PrNi exhibited self-focusing effect and a stronger saturable absorption. The reason for the difference was analyzed. The nonlinear refractive index n2, the third-order nonlinear susceptibility □(3), the molecular second-order hyperpolarizability □ of these complexes were with the magnitude of 10−18m2/W, 10−13 esu and 10−31 esu, respectively. All these results suggest that these materials are candidates for application in the different nonlinear optical fields at infrared band.

Synthesis, growth, structural and HOMO and LUMO, MEP analysis of a new stilbazolium derivative crystal: A enhanced third-order NLO properties with a high laser-induced damage threshold for NLO applications

A new organic third-order nonlinear optical crystal from stilbazolium family 2-[2-(4-methoxy-phenyl) vinyl]-1-methyl-pyridinium tetrafluoroborate (4MSTB) has been synthesized and grown by slow evaporation method for the first time. The grown crystal structure was confirmed by single crystal X-ray diffraction analysis, and it is revealed that the grown crystal crystallized in a triclinic crystal system with centrosymmetric space group P1¯. The HOMO and LUMO energies were calculated for the grown crystal explains charge transfer takes place within the molecule and confirms the suitability of the title crystal for NLO applications. The presence of various vibration modes of expected functional groups was identified by FT-IR analysis. The transmittance ability of the grown crystal was also analyzed by using UV–Vis–NIR spectral studies and shows that the crystal has no absorption of light in the entire Vis–NIR region. The thermal stability of the title crystal has been investigated by TGA/DTA studies and revealed that the material was thermally stable up to the melting point, 193°C. The hardness number, Meyer index, yield strength, and elastic stiffness constant has been estimated for the grown 4MSTB crystal using Vickers microhardness tester. Photoluminescence excitation studies showed green emission radiation occurred at 517nm. The dielectric properties of the grown crystal have been analyzed as a function of temperature over a wide range of frequency (50Hz–5MHz) by using LCR meter. The result of ac electrical conductivity of 4MSTB was found to be 5.25×10−5 (Ωm)−1. The laser damage threshold (LDT) energy for the grown crystal has been measured by using a Q-switched Nd:YAG laser as a source in single-shot mode (1064nm, 10Hz, 420mJ). The result of LDT indicates that grown title crystal has excellent resistance to laser radiation than those of known some inorganic NLO materials. The chemical etching studies were carried out to assess the perfection of the grown crystals. Its third-order nonlinear optical properties were investigated by Z-scan technique and proved that the 4MSTB crystal possesses two-photon absorptions (TPA) and the self-defocusing effect. The second-order molecular hyperpolarizability (γ) value at 632.8nm is calculated to be 3.555×10−34esu. The photoconductivity study of 4MSTB reveals that the negative photoconducting nature. The obtained all the results in the present work are making a 4MSTB promising candidate for the possible applications in optical switches, optical power limiter, and non-linear optical applications.

Nonlinear optical properties tuning in meso-tetraphenylporphyrin derivatives substituted with donor/acceptor groups in picosecond and nanosecond regimes.

meso-Tetraphenylporphyrin (TPP) and its two substituted derivatives (meso-tetrakis(4-cyanophenyl)porphyrin [TPP(CN)4] and meso-tetrakis(4-methoxyphenyl)porphyrin [TPP(OMe)4]) were synthesized. Their nonlinear absorption and refraction properties were studied using the Z-scan technique in the picosecond (ps) and nanosecond (ns) regimes. The open aperture Z-scan results reveal that TPP and TPP(CN)4 display an identical reverse saturable absorption (RSA) character in the ps and ns regimes. While TPP(OMe)4 exhibits a transition from saturable absorption (SA) to RSA in the ps regime and a typical RSA character in the ns regime. The closed aperture Z-scan results show that TPP(CN)4 and TPP(OMe)4 have regular enhancement of the magnitude of nonlinear refraction as compared to their parent TPP in both the ps and ns regimes. In addition, the second-order molecular hyperpolarizabilities (γ) of these three porphyrins are calculated, and the γ values of TPP(CN)4 and TPP(OMe)4 are remarkable larger than that of TPP. The introduction of the electron-withdrawing group CN and the electron-donating group OMe into TPP has enhanced its nonlinear refraction and γ value, and tuned its nonlinear absorption (TPP(OMe)4), which could be useful for porphyrin-related applications based on the desired NLO properties.

Study on third order nonlinear optical properties of a metal organic complex—Monothiourea–cadmium Sulphate Dihydrate single crystals grown in silica gel

The third order nonlinear optical properties of Monothiourea–cadmium Sulphate Dihydrate crystal were measured using a He–Ne laser (λ=632.8nm) by a Z-scan technique. The magnitude of nonlinear refractive index (n2) and nonlinear absorption coefficient was found to be 4.4769×10–11m2/W and 1.233×10−2m/W respectively. The third order non-linear optical susceptibility χ(3) was found to be in the order of 3.6533×10−2esu. The negative sign of non-linear refractive index shows the self-defocusing nature of the gel grown crystal. The second-order molecular hyperpolarizability γ of the grown crystal is 1.2822×10−33esu. Laser damage threshold was measured by using an Nd: YAG laser (1064nm). Photoconductivity studies of the gel grown crystal revealed that the crystal possesses positive photoconducting nature. The results obtained from Z-scan, laser damage threshold and photoconducting studies reveal that the crystal can be a possible candidate material for photonics device, optical switches, and optical power limiting application.

Nonlinear Scattering and Absorption Effects in Size-Selected Diphenylpolyynes

The nonlinear optical properties of monodispersed diphenylpolyynes with different chain length were studied by using a nanosecond pulsed laser excitation. A strong optical limiting response was detected at laser fluences above 0.35 J/cm2. The nature of the nonlinear effect as a function of the number of carbon atoms in the linear chain was investigated by the Z-scan technique, determining the molecular second-order hyperpolarizability γ. An interesting coupling was found between the decrease of scattering phenomena and the alignment of longer carbon chains in the focus region. The effect of an external highly intense electric field, combined with a detailed density functional theory (DFT) investigation, has been invoked to explain molecular arrangement, polarizability, isomery, and scattering of diphenylpolyynes. The interesting findings derived from our investigations demonstrate that phenyl-end-capped polyynes could be very interesting for various optoelectronic applications.

Theoretical Multipolar Atom Model Transfer in Nitro-Derivatives of N-Methylaniline

The nitroanilines are an example of compounds in which the coexistence of electron-rich and electron-deficient substituents, connected through a conjugated π-electronic system, makes their molecular second-order hyperpolarizability and second-harmonic generation efficiency particularly high. This property makes them extremely interesting from the point of view of charge density distribution analysis. The electron density of three isomeric molecules, i.e., N-methyl-2-nitroaniline, N-methyl-3-nitroaniline, and N-methyl-4-nitroaniline, was calculated theoretically through the multipolar atom model transfer. Two types of refinement models, i.e., multipolar atom model (MAM) and independent atom model (IAM), have been applied for analysis of model improvement concerning the electron-density parameters transfer. It results in a more precise molecular structure in terms of geometry and thermal displacement parameters along with a reduction of statistical refinement factors and residual electron densities. The pro...