Microscopic Hyperpolarizability Research Articles

Dispersion of the linear and nonlinear optical susceptibilities of disilver germanium sulfide from DFT calculations

The dispersion of the linear and nonlinear optical susceptibilities is calculated for disilver germanium sulfide (Ag2GeS3) using the all-electron full potential linearized augmented plane wave (FP-LAPW) method. Calculations are performed with four exchange correlations namely local density approximation (LDA), general gradient approximation (GGA), Engel–Vosko generalized gradient approximation (EVGGA), and modified Becke–Johnson potential (mBJ). Our calculations give a band gap of 0.40 eV (LDA), 0.42 eV (GGA), 1.03 eV (EVGGA), and 1.30 eV (mBJ) in comparison with our measured gap (1.98 eV). The mBJ exchange correlation gives the best agreement with experiment. We find that the calculated linear optical susceptibilities of Ag2GeS3 show considerable anisotropy which is useful for second harmonic generation and optical parametric oscillation. To analyze the spectra of the calculated χ 113 (2) (ω), χ 232 (2) (ω), χ 311 (2) (ω), χ 322 (2) (ω), and χ 333 (2) (ω), we have correlated the features of these spectra with the features of ɛ2(ω) spectra as a function of ω/2 and ω. From the calculated dominant component |χ 333 (2) (ω)|, we find that the microscopic second-order hyperpolarizability, β333, the vector components along the dipole moment direction is 41.2 × 10−30 esu at static limit and 222.9 × 10−30 esu at λ = 1064 nm.

Acentric Nonlinear Optical 2,4-Dihydroxyl Hydrazone Isomorphic Crystals with Large Linear, Nonlinear Optical Susceptibilities and Hyperpolarizability

A systematic ab initio study of the linear, nonlinear optical susceptibilities, and hyperpolarizability of noncentrosymmetric-monoclinic 2,4-dihydroxyl hydrazone isomorphic crystals (DHNPH) within density functional theory in the local density approximation (LDA), general gradient approximation (GGA), the Engel-Vosko generalized gradient approximation (EV-GGA) and modified Becke-Johnson potential (mBJ) has been performed. The complex dielectric susceptibility dispersion, its zero-frequency limit and the birefringence are studied. Using scissors’ corrected mBJ we find a large uniaxial dielectric anisotropy (-0.56) resulting in a significant birefringence (0.61). We also find that 2,4- DHNPH possess large second harmonic generation. The calculated second order susceptibility tensor components for the static limit |χ(111)(2)(0)| and |χ(111)(2)(ω)| at λ=1.9 μm (0.651 eV) and at λ = 1.064 μm (1.165 eV) are 53, 91, and 209 pm/V, respectively. A remarkable finding, applying the scissors’ correction has a profound effect on value, magnitude and sign of χ(ijk)(2)(ω). In additional we have calculated the microscopic hyperpolarizability, β(111), vector component along the principal dipole moment directions for the dominant component. We find that the value of β(111) equal to 47× 10(-30) esu, in good agreement with the measured value (48.2× 10(-30) esu).

Second Harmonic Generation and Hyperpolarizabilities of the Double-Cubane Compound [Sb7S8Br2](AlCl4)3: Chalcogenide in Ionic Liquids

Because noncentrosymmetric [Sb7S8Br2](AlCl4)3 single crystals possess a wide optical transparency region, it is a promising material for nonlinear optical applications. We have calculated the dispersion of linear and nonlinear optical susceptibilities including optical second harmonic generation (SHG) using a relaxed geometry. We find that the fundamental optical absorption edge situated at about 2.03 eV is in excellent agreement with the experimental data. Calculations of ε(2)(xx)(ω), ε(2)(yy)(ω), and ε(2)(zz)(ω) tensor components of the frequency-dependent dielectric function are presented. The single crystal possesses a considerable anisotropy of linear optical susceptibilities, which usually favors an enhanced phase matching conditions necessary to observe SHG and optical parametric oscillator (OPO) effects. Our calculations show that, in [Sb7S8Br2](AlCl4)3, |χ123(2)(ω)| is the principal tensor component having the highest value of SHG at zero frequency limit as well as at 1.165 eV (λ = 1064 nm) laser wavelength generation. The microscopic second-order hyperpolarizability, β123, of the dominant SHG component is calculated at the static limit and at λ = 1064 nm.

Effect of modified donor units on molecular hyperpolarizability of thienyl-vinylene nonlinear optical chromophores

Highly efficient and thermally stable nonlinear optical chromophores based on the phenyl vinylene thiophene vinylene (FTC) donor-π-acceptor structure have been synthesized and investigated. The donor part of the chromophores was modified with additional donor units, resulting in the enhanced nonlinear optical property with large molecular hyperpolarizability. Hyper-Rayleigh scattering measurement indicated nearly threefold increase of the molecular hyperpolarizability for novel chromophores compared with the benchmark FTC chromophore. Furthermore, measurement of the electro-optic coefficient confirmed that enhancement of microscopic molecular hyperpolarizability of the chromophores can be effectively translated into macroscopic electro-optic property. Measured electro-optic coefficients were nearly twofold larger than that for the benchmark FTC. Thermal analysis indicated that the synthesized chromophores showed the excellent temperature stability with decomposition temperatures up to 280 °C.

Control of the Orientational Order and Nonlinear Optical Response of the “Push−Pull” Chromophore RuPZn via Specific Incorporation into Densely Packed Monolayer Ensembles of an Amphiphilic 4-Helix Bundle Peptide: Second Harmonic Generation at High Chromophore Densities

The macroscopic nonlinear optical response of the "push-pull" chromophore RuPZn incorporated into a single monolayer of the amphiphilic 4-helix bundle peptide (AP0) covalently attached to a solid substrate at high in-plane density has been measured. The second-order susceptibility, chi(zzz), was found to be in the range of approximately 15 x 10(-9) esu, consistent with a coherent sum of the nonlinear contributions from the individual chromophores (beta) as previously measured in isotropic solution through hyper-Rayleigh scattering as well as estimated from theoretical calculations. The microscopic hyperpolarizability of the RuPZn chromophore is preserved upon incorporation into the peptide monolayer, suggesting that the chromophore-chromophore interactions in the densely packed ensemble do not substantially affect the first-order molecular hyperpolarizability. The polarization angle dependence of the second harmonic signal reveals that the chromophore is vectorially oriented in the two-dimensional ensemble. Analysis of the order parameter together with information obtained from grazing incidence X-ray diffraction help in determining the chromophore orientation within the AP0-RuPZn monolayer. Taking into account an average pitch angle of approximately 20 degrees characterizing the coiled-coil structure of the peptide bundle, the width of the bundle's tilt angle distribution should be sigma < or = 20 degrees, resulting in a mean value of the tilt angle 23 degrees < or = theta(0) < or = 37 degrees.

Synthesis, third-order nonlinear absorption and refraction of fullerene dyads containing fluorene

Two new fullerene–fluorene dyads, N-methyl-2-(2-fluorenyl)-3,4-[60]fuller-pyrrolydine ( 1) and N-methyl-2-(2-fluorenyl)-3,4-[70]fullerpyrrolydine ( 2), were synthesized and their structures were confirmed by MALDI-MS, 1H NMR and FT-IR. Their electrochemical and optical properties were investigated by cyclic voltammetry and Z-scan technique, including, electronic potentials, two-photon absorption cross-sections ( σ 2), nonlinear refractive indexes ( n 2), microscopic second-order hyperpolarizabilities ( γ R ) and third-order nonlinear susceptibilities ( χ I ( 3 ) and χ R ( 3 ) ). Importantly, the χ I ( 3 ) and σ 2 in 2 were increased above 35% due to [70]fullerene unit than that of 1.

Ultrafast optical nonlinearities and figures of merit in acceptor-substituted 3,4,5-trimethoxy chalcone derivatives: Structure-property relationships

By performing both Z-scan and transient transmission measurements with 130 fs laser pulses in the near infrared region, we investigated structure-property relationships for χ(3) in acceptor-substituted 3,4,5-trimethoxy chalcone derivatives. We determined all nonlinear parameters, including two-photon absorption (2PA) cross section, 2PA-induced excited-state absorption (ESA) cross section, microscopic second-order hyperpolarizability, and lifetime of the excited state in these molecules. We found that the microscopic second-order hyperpolarizability γR and 2PA cross section σ2PA in chalcone derivatives increase as the acceptor strength of the molecules increases, which demonstrates an enhancement in optical nonlinearities by simple structural variations. We evaluated the one-photon, two-photon, and effective three-photon figures of merit for acetone solutions of chalcone derivatives at irradiance of 100 GW/cm2. Furthermore, we observed optical limiting behavior in these compounds, which result from both 2PA and 2PA-assisted ESA. These results indicated that chalcone derivatives are a promising candidate for applications on nonlinear photonic devices.

Problems in the comparison of theoretical and experimental hyperpolarizabilities revisited

The relationship between nonlinear susceptibilities and hyperpolarizabilities defined using different conventions is reexamined. In previous work [Willetts et al., J. Chem. Phys. 97, 7590 (1992)], relations between different conventions for microscopic hyperpolarizabilities have been derived, but the application of the corresponding conversion factors led to several inconsistencies. It is shown that different conventions for macroscopic susceptibilities have to be taken into account, too, in order to arrive at consistently comparable values. The complete set of conversion factors between several conventions are given for second harmonic generation, electric field induced second harmonic (EFISH) generation, and third harmonic generation. As an illustration, experimental EFISH and hyper-Rayleigh scattering results of p-nitroaniline are compared with each other and with recent results of ab initio computations including solvation effects. Several problems in the comparison of computational and experimental values are also discussed.

Synthesis, molecular structure, spectroscopic studies and second-order nonlinear optical behaviour of N, N′-(2-hydroxy-propane-1,3-diyl)-bis(5-nitrosalicylaldiminato- N, O)-copper(II)

N, N′-(2-Hydroxy-propane-1,3-diyl)-bis(5-nitrosalicylaldiminato- N, O)-copper(II) has been synthesized. The crystal structure has been determined by X-ray diffraction analysis, and linear optical characterization has been determined by UV–vis spectroscopy. It was found that the molecule under investigation has solvatochromic behaviour in the UV region, implying non-zero microscopic first hyperpolarizability. To reveal the microscopic nonlinear optical (NLO) properties, the static first hyperpolarizabilities ( β) and the electric dipole moments ( μ) were evaluated by using the ab initio finite field (FF) method. According to the results of the FF calculations, the synthesized compound exhibits non-zero β values, and it might have microscopic NLO behaviour.

Study On The Second Order Optical Properties Of N-(2,4-Dichloro)-Salicylaldimine

N-(2,4-Dichloro)-salicylaldimine was synthesized, characterized by elemental analysis, FT-IR, and UV-visible spectroscopy, and its crystal structure was determined. The title compound is almost planar and contains short intramolecular O-H. . .N hydrogen bonds [O1-N1 2.601(1) A° ]. It remains transparent in the visible region and has solvatochromic behavior in the UV region in the range 198 - 349 nm, implying non-zero microscopic first hyperpolarizability. The ab-initio quantum mechanical calculations (finite field second-order Møller Plesset perturbation theory) of the studied compound have been carried out to compute the electric dipole moment (μ) and the first hyperpolarizability (β ) values. The ab-initio results also show that this ligand might have microscopic nonlinear optical behavior with non-zero values.

Nonlinear optical properties, synthesis, structures and spectroscopic studies of N-(4-nitrobenzylidene)- o-fluoroamine and N-(3-nitrobenzylidene)- p-fluoroamine

N-(4-nitrobenzylidene)- o-fluoroamine ( 1) and N-(3-nitrobenzylidene)- p-fluoroamine ( 2) have been synthesized. The crystal structures of both compounds have been defined by X-ray diffraction analysis, and characterized by FT-IR and UV-visible instrumental methods. The recorded spectrum by UV-visible spectroscopy for the investigated compounds show good transparency in the visible region, and have solvatochromic behavior in the UV region, implying nonzero microscopic first hyperpolarizability. We also report ab initio quantum chemical calculations of the electric dipole moments ( μ) and the first hyperpolarizabilities ( β) of the studied compounds. Our results suggest that the investigated ligands might have microscopic nonlinear optical (NLO) behavior with nonzero values.

The investigation of nonlinear optical properties of N-(3-fluorophenyl)naphthaldimine

A new ligand N-(3-fluorophenyl)naphthaldimine (C 17H 12NOF) has been synthesized. The physical properties and structure of this ligand have been characterized by X-ray diffraction analysis, elemental analysis, FT-IR, 1H-NMR and UV–visible spectroscopies. It is found that the title compound has solvatochromic behavior in the UV and visible regions, implying non-zero microscopic first hyperpolarizability. The electric dipole moment ( μ) and the first hyperpolarizability ( β) values of the investigated molecule have been computed using ab initio quantum mechanical calculations (finite field second-order Møller Plesset perturbation theory). The calculation results also reveal that the synthesized molecule might have microscopic nonlinear optical (NLO) behavior with non-zero values.

Optical poling of oligoether acrylate photopolymers doped by 1- H-pyrazolo[3,4-b]quinolines derivative chromophores

Second harmonic generation excited by Nd:YAG laser ( λ=1.32 μ m) was observed during the investigation of second-order optical poling process in 1- H-pyrazolo[3,4-b]quinolines chromophores incorporated within the oligoether acrylate (OEA) photopolymer matrices. We have found that the observed SHG output is correlated well with the values of corresponding dipole moments. Due to incorporation of the chromophore into photopolymer matrices second-order microscopic hyperpolarizabilities of the composites substantially increase (up to 3.01 pm/V). The investigated composites possess long-lived photopolarized states and after about 10 5 laser pulses the output SHG output signal did not decrease below 75% compared to the SHG signal in the beginning of the treatment. Optimal conditions of the optical poling corresponded to power density of the doubled frequency beam about 0.024 GW/cm 2 and chromophore content about 5.2% (in weighting unites).

Electric field induced second harmonic generation: Second and third-order hyperpolarizabilities of 4-amino-4′-nitrodiphenyl sulfoxide

The second-order hyperpolarizability (β), and the third-order hyperpolarizability (γ) of 4-amino-4′-nitrodiphenyl sulfoxide (ANDSO) has been determined using the technique of electric field induced second harmonic (EFISH) generation in liquid. The third order macroscopic nonlinear susceptibility of ANDSO was first determined by comparing the intensity of the frequency doubled Nd:YAG laser pulse from the EFISH cell containing ANDSO solution to that of a reference material. The microscopic hyperpolarizabilities γ and β for ANDSO were extracted from the nonlinear susceptibility using local field factors, bond additivity concept and knowledge of the dipole moment of the molecule. Comparison of β and γ obtained in the present work to those obtained by other investigators for other molecules shows a superior microscopic nonlinear properties for ANDSO.

Femtosecond Third-Order Optical Nonlinearity of Conjugated Polymers Consisting of Fluorene and Tetraphenyldiaminobiphenyl Units: Structure−Property Relationships

Femtosecond time-resolved optical Kerr effect technique has been used to investigate the third-order nonlinear optical (NLO) properties of a series of conjugated polymers consisting of fluorene and/or tetraphenyldiaminobiphenyl (TPD) units designed to elucidate structure−property relationships for the microscopic second-order hyperpolarizability γ in polymeric materials. The γ per repeated unit of the series of polymers has off-resonant values at 830 nm in the range of 2.0 × 10-33−2.4 × 10-31 esu, demonstrating a large modulation of nonlinear optical response by simple structural variations. The γ values of alternative copolymers containing fluorene and TPD moieties are 2 orders of magnitude higher than the γ value of the homopolymer polyfluorene, revealing the vital role of the strong electron donor TPD in the NLO enhancement. The fluorene segment was found to result in 4-fold enhancement of γ in TPD-containing copolymers compared to p-phenylenevinylene segment, indicating that the planar rigid ring of fluorene is an efficient third-order NLO chromophore. No relationship between the magnitude of γ and the optical band gap was found. The large variation of γ value with molecular structure of these polymers can be explained by molecular exciton theory other than the band theory.

On the Relation Between Conformational Changes and Optical Properties in Oligothiophenes, 2. Linear and Nonlinear Optical Properties

The dependence of microscopic electronic non-resonant polarizabilities (a) and second-order hyper-polarizabilities (y) of short oligothiophenes on the mutual torsional ring orientation was investigated by employing the time-dependent Hartree-Fock method within the AM1 approximation. The a and y quantities exhibit the uniform shape of the torsional dependence regardless of the mutual ring's orientations for all the systems under study (minima occur for perpendicular geometries and maxima are indicated for planar structures). The frequency dependence of y hyperpolarizability below the first resonance frequency is fairly well evaluated in the form of a simple power series. The trends of AM1 results agree with the current theoretical treatments as well as experimental data/

Macroscopic and microscopic second-harmonic response from subphthalocyanine thin films

The second-harmonic generation (SHG) yield of both evaporated and spin-coated films of some tri-substituted subphthalocyanines has been measured for three linear polarizations of the fundamental beam. Partial molecular ordering in the spin-coated films was achieved by the corona poling technique. For the evaporated films the ordering is obtained through the evaporation process itself. By proper fitting of the SHG yield data and assuming C∞v symmetry the three nonzero independent components, χ31(2), χ15(2) and χ33(2), of the susceptibility tensor have been determined for the two types of films. Kleinman symmetry condition (χ31(2)=χ15(2)) is not obeyed. Values close to 10−9 esu have been obtained for the highest χ31(2) component of the spin-coated films containing trioctylsulfonylsubphthalocyanine molecules. For the evaporated films the susceptibility values are somewhat higher, indicating a significant degree of molecular ordering. For both types of films χ33(2)≪χ31(2), χ15(2), at variance with the case of linear molecules. From a statistical analysis of the macroscopic SHG emission the nonzero components of the microscopic (molecular) hyperpolarizability tensor, β15, β31 and β33, have also been estimated. The results indicate that β33≈0, and that β31 and β15 are dominant in accordance with the pyramid-shaped molecular geometry. The additional inplane components βyxx=−βyyy=βxxy=−β22 appearing in the C3v molecular symmetry cannot be determined from the macroscopic data.

Precise study of nonlinear optical coefficients and hyperpolarizabilities in cold-drawn and poled ferroelectric Nylon 11 films

This paper presents a precise study of second-order optical nonlinearity of uniaxially cold-drawn and poled ferroelectric Nylon 11 films. The effects of drawing and poling on refractive indices and second-order nonlinear optical coefficients have been investigated. Drawing caused increase of refractive index (n) parallel to the drawing direction nX, and decrease of n perpendicular to drawing direction in the plane of film nY, as well as decrease of n on the poling direction parallel to film thickness direction nZ. Poling caused significant increase of nZ and decrease of nY. These n results imply that poling aligns the molecular chains so that carbonyl groups in Nylon backbone orient in the poling direction (Z-axis). Cold-drawn and poled Nylon 11 films belong to the mm2 point group. Dependence of second-order harmonic generation (SHG) intensity on incidence angle, i.e., Maker fringe pattern, could be precisely fitted using five independent nonzero tensor components, d33, d32, d31, d15, and d24. However, Kleinman symmetry was not satisfied: d31≠d15 and d32≠d24. The tensor components d33, d31, d15, and d24 increase with increasing remanent polarization, whereas the value of d32 was negligibly small irrespective of the intensity of the remanent polarization. Tensor components of microscopic first-order hyperpolarizability, βzxx, βzyy, βzzz, βxxz, and βyyz were determined. Tensor component βzzz was the largest and βzxx had negative sign. Second-order nonlinearity was largely suppressed in the vicinity of the melting point of Nylon 11.

On the Calculation of Local Field Factors for Microscopic Static Hyperpolarizabilities of Molecules in Solution with the Aid of Quantum-Mechanical Methods

We present a simple computational method to connect the computed ab initio values of static dipole polarizabilities and hyperpolarizabilities of molecules in solution with their experimental counterparts. The connection is done in terms of local field factors. We show that formulas used by experimentalists are not adequate, and that they can be replaced by a reformulation of the quantum-mechanical codes for the calculation of (hyper)polarizabilities in solution by using a realistic description of the solvent reaction field (i.e., a cavity with the proper molecular shape). This reformulation leads to an additional set of hyperpolarizability values which take into account local modifications to the external static field. This second set of values has a direct relation with the macroscopic susceptibility tensors and, when compared to that derived from standard calculations, allows one to evaluate realistic local field factors.

Second harmonic generation in push-pull ethylenes: Influence of chirality and hydrogen bonding

The effect of chiral substituents and hydrogen bonding functional groups on the microscopic and macroscopic second-order non-linearities in some donor-acceptor substituted ethylenes has been investigated. It appears that extensive intramolecular and intermolecular hydrogen bonding helps to improve both the microscopic hyperpolarizability (β) as well as the powder second harmonic generation (SHG) efficiency in these compounds. The substitution of the chiral a-methylbenzylamine donor guarantees a non-centrosymmetric structure. Cocrystallization with triphenylphosphine oxide (TPPO) does not appear to yield better SHG efficiency in the a-methylbenzylamine substituted ethylene compound which has an extended hydrogen bonding network.