Large Nonlinear Optical Susceptibility Research Articles

A first-principles study of linear and nonlinear optical properties of 4-nitro-4′-methylbenzylidene aniline

First-principles calculations of two second-order optical response functions as well as the dielectric function for 4-nitro-4(')-methylbenzylidene aniline are performed. Specifically, we evaluate the dielectric function and the second-harmonic generation (SHG) response coefficient over a wide frequency range. Electronic structure obtained from the full-potential projected augmented wave method is adopted in the calculation of optical properties. The calculated results of the refractive indices and the SHG are in good agreement with the experimental values. The linear and nonlinear optical spectra are analyzed and the origins of the peaks in the spectra are discussed in terms of the calculated electronic structure. It is found that the origin of the large nonlinear optical susceptibility is the charge transfer due to the strong "push-pull" effect. The study of the contributions of different transitions to the SHG coefficients shows that the virtual electron process is main. The contribution to the largest component chi(11) ((2)) of the virtual hole process is about 30% of the total static limit of the SHG coefficient. The prominent features in the spectrum of chi(11) ((2)) are successfully correlated with the features of the linear dielectric function epsilon(omega) in terms of single-photon and two-photon resonances.

Imaging metal oxide nanoparticles in biological structures with CARS microscopy

Metal oxide nanomaterials are being used for an increasing number of commercial applications, such as fillers, opacifiers, catalysts, semiconductors, cosmetics, microelectronics, and as drug delivery vehicles. The effects of these nanoparticles on the physiology of animals and in the environment are largely unknown and their potential associated health risks are currently a topic of hot debate. Information regarding the entry route of nanoparticles into exposed organisms and their subsequent localization within tissues and cells in the body are essential for understanding their biological impact. However, there is currently no imaging modality available that can simultaneously image these nanoparticles and the surrounding tissues without disturbing the biological structure. Due to their large nonlinear optical susceptibilities, which are enhanced by two-photon electronic resonance, metal oxides are efficient sources of coherent anti-Stokes Raman Scattering (CARS). We show that CARS microscopy can provide localization of metal oxide nanoparticles within biological structures at the cellular level. Nanoparticles of 20 - 70 nm in size were imaged within the fish gill; a structure that is a primary site of pollutant uptake into fish from the aquatic environment.

オクタデシルトリクロロシラン処理された石英ガラス基板上のポリ（３‐ヘキシルチオフェン）薄膜の形態と非線形光学特性

Polythiophene derivatives in π-conjugated polymers have been attracting the attention of researchers as derivatives retaining extensively potential applications in optoelectronics such as optical switches, optical logic circuits, optical integrated circuit (IC) and so forth. As π-conjugated polymers have high non-localized π electron density, the thin film prepared by π-conjugated polymers has the possibility of a large third order nonlinear optical susceptibility occurring from the thin film. In this study, the π-conjugated polymer used is regioregular poly (3-hexylthiophene-2, 5-diyl) {P3HT}. The substrate preparing P3HT thin film is quartz glass treated by octadecyltrichlorosilane (ODTS) or hexamethyldisilazane (HMDS). P3HT thin films are prepared by a drop-casting on it formed on the surface of quartz glass with self-assembling monolayer (SAM) [ODTS or HMDS]. The molecular orientation or alignment of P3HT thin films with and without SAM is performed using an X-ray Diffraction (XRD) spectrometer and UV/Vis spectrophotometer. Based on these results, the nonlinear optical characteristics of P3HT thin films with and without SAM are performed and investigated with the third harmonic intensity measured by the Maker fringe method.

Large‐Size Bulk and Thin‐Film Stilbazolium‐Salt Single Crystals for Nonlinear Optics and THz Generation

AbstractWe present new stilbazolium salt DSTMS (4‐N,N‐dimethylamino‐4′‐N′‐methyl‐stilbazolium 2,4,6‐trimethylbenzenesulfonate) with both high second‐order nonlinear optical properties and very favorable crystal growth characteristics. We are able to obtain very large area bulk single crystals of more than 3 × 3 × 0.2 cm3 with a high optical quality without using seed crystals by using low‐temperature solution growth. We also demonstrate the growth of single crystalline thin films of DSTMS with an area of up to 6 × 5 mm2 and a thickness between 5–30 μm. Nonlinear optical measurements reveal that DSTMS possesses large nonlinear optical susceptibilities with χ111(2) = (430 ± 40) pm V–1 at 1.9 μm. Highly efficient generation of broadband THz waves with THz electric field strengths of more than 4 kV cm–1 using 160 fs laser pump pulses at a wavelength λ = 1.45 μm and DSTMS crystals has been demonstrated.

Electronic Origin for Enhanced Nonlinear Optical Response of Complexes from Tetraalkylammonium Halide and Carbon Tetrabromide: Electrostatic Potentials of Intermolecular Donor–Acceptor Dyads

Electronic origin for nonresonant enhancement of nonlinear optical response in the complexes formed from tetraalkylammonium halide and carbon tetrabromide is provided in view of electrostatic potentials of intermolecular donor (halide ion)-acceptor (CBr(4)). The calculated electrostatic potentials of donor-acceptor range from -4.83 to -7.70 kcal mol(-1) and show a decreasing order of [Et(4)Cl(-)Br] > [Et(4)Br(-)Br] congruent with [Et(4)I(-)Br] > [Bu(4)Br(-)Br]. The calculated second-order susceptibilities of solid complexes are in an increasing order of [NEt(4)ClCBr(4)] < [NEt(4)BrCBr(4)] congruent with [NEt(4)ICBr(4)] < [NBu(4)BrCBr(4)C(3)H(6)O]. It has been shown that the donor/acceptor dyads make the exclusive contribution to nonlinear optical response. A large size of halide or tetraalkylammonium ion results in a small electrostatic potential and large nonlinear optical response in these charge-transfer complexes. It indicates that a small supermolecular interaction will create a large nonlinear optical response, and it gives a clue to design the molecular complexes with large non-linear optical susceptibility.

Molecular Engineering of Octupolar NLO Molecules and Materials Based on Bipyridyl Metal Complexes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Molecular Engineering of Octupolar NLO Molecules and Materials Based on Bipyridyl Metal Complexes

Coordination compounds are of particular interest for the design of new chromophores with large nonlinear optical (NLO) susceptibilities. They offer a wide range of metals with different oxidation states and ligands, which can give rise to tunable electronic properties. Metal ions are excellent templates to build 2D and 3D octupolar NLO-phores. Their associations with functionalized bipyridyl ligands give rise to octahedral and tetrahedral metal complexes with large first-order hyperpolarizabilities. The ability to functionalize these octupoles allows their incorporation into macromolecular architectures such as polymers and metallodendrimers, We also show in this Account two approaches to induce noncentrosymmetry at the macroscopic level, either by supramolecular organization or by the all optical poling procedure.

Au/TiO2/SiO2 sandwich multilayer composite films with large nonlinear optical susceptibility

Abstract Au/TiO 2 /SiO 2 sandwich composite multilayer films were deposited by alternating multitarget magnetron sputtering technique. Annealing process was performed for as-growth. Au particles appeared between the layers and grew with the increasing of the annealing temperature. The surface plasmon resonance of the annealed films is around 570–590 nm. The third-order nonlinear susceptibility was measured with the backward degenerate four wave mixing (DFWM) scheme at a 532 nm wavelength. The calculated values of χ (3) at 532 nm of the composite films are larger than 1.02 × 10 −6 esu. We assume the multilayer sandwich topology of the Au/TiO 2 /SiO 2 composite films has greatly enhanced the local field factor f and caused a larger χ (3) which is even not measured at the wavelength near the surface plasmon resonance of the composite materials.

Second-harmonic generation in nonpolar chiral materials: relationship between molecular and macroscopic properties

An oriented gas model for the second-order nonlinear optical response for optical second-harmonic generation in axially aligned nonlinear optical chromophores in chiral media is presented. Design criteria for the alignment of chromophores possessing Kleinman-disallowed traceless symmetric second-rank tensor hyperpolarizabilities β resulting in large nonlinear optical susceptibilities χ(2) are enumerated. These chromophores could be oriented in high-density, highly ordered structures due to the absence of dipolar interactions resulting in exceptionally large χ(2) values. The alignment of chromophores that have C2v or Dn(n&gt;2) symmetry in two chiral nonpolar symmetry groups for the medium, D∞ and D2, are considered. Criteria for response optimization and several physical examples are described. Additionally, certain nonpolar symmetry groups for the medium, of which the most easily realizable is probably D2, also admit Kleinman-allowed octupolar susceptibilities for which the optimum chromophore alignment is discussed.

Three dimensional molecular stacking and functionalities of aminonaphthoquinone by intermolecular hydrogen bondings and interlayer π–π interactions

Three dimensional molecular stacking of aminonaphthoquinones affecting largely on their 3rd order nonlinear optical property was evaluated by X-ray crystal analysis. It was found that the intermolecular hydrogen bondings and the interlayer π–π interactions played a significant role in producing large bathochromic shifts of absorption maximum in solid state, and gave large 3rd order nonlinear optical susceptibility. Molecular symmetry and substituent effects on their physical properties were also correlated with their molecular stacking in crystals.

Spectral Properties of tetrathiabenzoquinones and their self-assembly in the solid state

Bis(1,4-dithiacyclohexano)[2,3-b:2′,3′-e]-1,4-benzoquinone 3a and analogous cyclic dithiaquinone derivatives were synthesized. The difference (Δλ) in λmax of these dyes between the solution phase and vapor deposited thin film indicates the degree of strength of the intermolecular π-π interactions in the solid state. The Δλ values were largely affected by the interlayer distances and the steric requirements of the molecules. The three dimensional molecular stacking of dye 3a was evaluated by X-ray crystal analysis and the substituent effects on the properties of analogous dyes were evaluated by the MOPAC and AMPAC calculation methods. The vapor deposited thin film of dye 3a gave large 3rd order nonlinear optical susceptibility. The intermolecular π-π interactions of the dye molecules play an important role for these special functionalities.

Investigation of thermochromic polydiacetylenes by AFM

In recent years, Polydiacetylenes (PDAs) have attracted a great deal of attention owing to their extremely large third order non-linear optical susceptibilities, which are believed to result from their molecular arrangement. It is also known that a specific sub-class of these PDAs, namely, the urethane - substituted PDAs such as ETCD (Bis ethyl urethane of 5,7 dodecadiyn 1,12 diol) and IPUDO (Bis isopropyl urethane of 5,7 dodecadiyn 1,12 diol) exhibit thermochromism. This is the underlying principle behind the potential use of such PDAs in optical devices such as holographic elements, spatial light modulators etc. The surface properties of these PDA materials are critical to their performance as optical devices. There are several indications from Raman Spectroscopy that PDA crystals have surface features distinct from the bulk. Also PDA - IPUDO has been identified as a material with a variable surface. We have investigated the free standing single crystals of the monomeric and polymeric forms of PDA - ETCD and IPUDO by Atomic Force Microscopy (AFM). Large scale as well as molecular resolved images were obtained.

Femtosecond optical correlation using four-wave mixing

A matched-filter optical correlator was built using four-wave mixing in an air-stable degenerate ground state conjugated polymer. The four-wave mixing architecture results in a highly parallel optical computer which completes an image correlation in less than 160 fs. The images correlated were each 5000 pixels in size, resulting in a peak data processing rate of 3 × 10 16 operations per second. The results demonstrate the application of the large third order nonlinear optical susceptibilities of conjugated polymers in optical computing, achieving data processing rates that cannot be approached by current electronic computers.

Processing thin films of KNbO3 for optical waveguides

Abstract Thin film waveguides of ferroelectric materials hold great promise for use in active integrated optics devices because of the high optical confinement possible in a thin film structure. KNbO3 is an attractive material for active devices because it possesses large nonlinear optical susceptibilities and large electro-optic coefficients. KNbO3 films with low optical losses are required to produce efficient devices. Epitaxial films of KNbO3 (110) have previously been deposited on single crystal MgO (100) using ion beam sputtering techniques. However, these films contained microstructural defects due to the large lattice mismatch (>4.0%) between KNbO3 and MgO which resulted in high optical losses. Recent work has focused on determining the relationships between microstructure and optical loss through the use of lattice matched substrates. Film composition, epitaxial quality and optical properties of KNbO3 films deposited on MgO and MgAl2O4 have been investigated and are compared.

Design and synthesis of ferroelectric liquid crystals. 15.1FLC materials for nonlinear optics applications

Abstract We have recently reported the first FLCs designed specifically for large second order nonlinear optical (NLO) susceptibility χ(2); a series of o-nitro-1-methylheptyloxy biphenylbenzoates and phenyl biphenylcarboxylates. Properties of a stable room-temperature C* mixture of two such components (1:1 W316/W317 = MX5679) are presented. The nonlinear susceptibility, as evidenced by the Type 1 eeo deff for second harmonic generation (SHG) from 1,064 nm light for MX5679 is indeed large relative to other FLCs which have been evaluated for χ(2) (deff (ZLI3654) = 0.0016 pm/V, deff (SCE9) = 0.0037 pm/V, deff (MX5679) = 0.16 pm/V). The synthesis and some properties of second-generation FLCs designed for NLO applications is also described.

An Approach to the Design of Ferroelectric Liquid Crystals with Large Second Order Electronic Nonlinear Optical Susceptibility

Abstract Ferroelectric liquid crystal thin films in the Clark-Lagerwall surface-stabilized geometry exhibit well known spontaneous polar orientation of functional groups. The symmetry of the system thus allows the existence of bulk electronic second order nonlinear hyperpolarizability x(2) within thc context of the simple dipolar model. For all FLC materials examined to date, however, the magnitude of x(2) is small, presumably since the particular functional group arrays oriented along the polar axis possess small molecular hyperpolarizdbility β. Using the Boulder Model for the molecular origins of the polar order occurring in FLC films, it is possible to design materials with functionalized aromatic rings oriented along the polar axis of the film. Since such functional arrays may show respectable values of β, it should be possible to obtain FIX films (both low molecular weight and polymeric) with useful magnitude of x(2) using this approach. Results of initial experiments aimed at design of FLC materials...

Second-order nonlinear optical properties and polymorphism of benzophenone derivatives

Some di-substituted benzophenone derivatives were found which have large nonlinear optical susceptibilities and short cut-off wavelengths of about 400 nm. The second harmonic generation (SHG) activity of 4-methoxy-4′-nitrobenzophenone, which was relatively suitable for a frequency doubler among benzophenone recrystallization rate. The difference in SHG activity was attributed to polymorphism, based on results of X-ray analysis and differential scanning calorimetry.

Scalar and vector holographic gratings recorded in a photoanisotropic amorphous As_2S_3 thin film

Theoretical explanations of the kinetics of scalar and vector holographic gratings are developed, and experimental results are obtained in amorphous AS(2)S(3) thin films. The large nonlinear-optical susceptibilities are evaluated from experimental data in the vicinity of the fundamental absorption edge, and it is found that chi((3))(1111) congruent with 3.2 x 10(-2) esu and chi((3))(1122)/chi((3))(1111) congruent with 0.98.

Phase-matched second harmonic generation in potassium malate

The linear and nonlinear optical properties of the organic crystal potassium malate (KM) are investigated. High birefringence and a broad transmission range combined with a rather large nonlinear optical susceptibility were found in this material. Phase-matched second harmonic generation is possible down to about 488 nm of fundamental wavelength.

An exceptionally large linear electro-optic effect in the organic solid MNA

The dc linear electro-optic effect and the x-ray crystal structure of the organic molecular solid 2-methyl-4-nitroaniline (MNA) have been studied. Of two crystal orientations measured, one polar orientation was found to have an exceptionally large figure of merit for electro-optic phase retardation, comparable to that of LiNbO3. Comparison with second harmonic generation results demonstrates that the linear electro-optic effect in MNA is primarily electronic in nature. The origin of the large macroscopic second order nonlinear optical susceptibility is traced to a single large component of the corresponding microscopic molecular susceptibility.