Nonlinear Optical Coefficient D33 Research Articles

The role of doping technology in the formation of nonlinear optical properties of LiNbO3:Mg:B crystals

Nonlinear optical coefficients dij were calculated quantitatively for two series of LiNbO3 crystals double-doped with Mg and nonmetallic B obtained by the methods of the solid-phase (SP) synthesis and homogeneous introduction (HG) of impurities. The addition of boron and the presence of MgLi extrinsic defects increased the efficiency of second-harmonic conversion. Homogeneously doped crystals have been found to be the most suitable medium for second-harmonic generation (SHG). The high value of the total nonlinear optical coefficient d33 (−70.742(5) × 10−9 cm/statV) and the extremely low photorefractive response make the LiNbO3:Mg:B crystal (4.2 mol%) obtained by the HG method promising for use in nonlinear optics.

Effect of magnesium and zinc doping of lithium niobate crystals on nonlinear optical characteristics

The theoretical and experimental values of nonlinear optical susceptibilities for lithium niobate crystals double doped with cations (Zn2+:Mg2+) with similar concentrations obtained using the method of direct and homogeneous impurity introduction were analyzed. The length of Li-O bonds in double-doped crystals (LiNbO3:Zn2+:Mg2+) determined the value of the nonlinear optical second harmonic generation (SHG) coefficients. It was found that impurity and intrinsic defects make a positive contribution to the tensor coefficients of the second-order nonlinear optical susceptibility (dij). The results indicated that the LiNbO3:Zn2+:Mg2+ (3.83:0.97 mol%) crystal is the most suitable medium for SHG application among the crystals studied in the paper, as it showed the maximum calculated value of the nonlinear optical coefficient d33 which was equal to −55.26(2) × 10−9 cm/statV. The measured second harmonic conversion efficiency for this crystal was η = 36%.

Push-pull chromophores with π-deficient benzoazine and π-excessive thiophene cores in conjugated bridge as sources of quadratic nonlinear optical activity of composite polymer materials and molecular glasses

Impact of π-deficient heterocyclic core (A′) in conjugated bridge of D-π-A′-π-A chromophores (D = N,N-dihexylaniline, A = tricyanofuran derivative) on optical and thermal properties has been investigated. Three new chromophores with vinyl-hetaryl-vinyl bridges containing π-deficient benzoazine moiety (quinoxaline, quinoxalinone and quinoline) have been synthesized along with new chromophores with vinyl-thiophene-vinyl bridge containing π-excessive heterocycle and short vinylene bridge, and their properties are compared to reveal the role of π-deficient hetaryl moiety. Their linear optical properties were systematically investigated by UV–Vis spectroscopy and molecular nonlinear optical (NLO) characteristics were predicted by DFT calculations. As the aromaticity of the heterocycle in the bridge increases, a hypochromicity and hypsochromic shift of the absorption maximum manifest themselves in the UV–Vis spectra, the origin of electron transitions was studied by TD-DFT with CAM-B3LYP and PBE0 density functionals. The calculated first hyperpolarizability, βtot, for A′ = quinoxaline, quinoline and thiophene, was shown to be almost independent on the type of the π-bridge core, being in a narrow interval 800–831⋅10−30 esu, while for A′ = quinoxalinone βtot is essentially higher (996⋅10−30 esu). All chromophores exhibit good thermal stability (Td > 192 °C). Thin films of composite polymer materials with PMMA matrix and studied chromophores as guests as well as of some molecular glasses were spin-cast and corona-poled, and their quadratic NLO activity was measured by two different techniques. For materials with guest chromophores containing quinoxalinone, quinoxaline and thiophene moieties in the bridges NLO coefficients d33 were found to be rather close and reached 76 pm/V, what is almost 3 times higher than that for polymer film with quinoline-based chromophore. Rather high values of NLO coefficients for molecular glasses based on chromophores with quinoline, thiophene and quinoxalinone cores were obtained: 52, 124 and 132 pm/V, respectively, which notably exceed the values for composite materials with these chromophores as guests.

Polymer Matrix Effect on Nonlinear Optical Response of Composite Materials Doped with a Chromophore Containing a Divinylqunoxaline π-Electron Bridge

The effect of polymer matrices on the nonlinear-optical properties of composite materials with guest chromophores containing a divinylquinoxaline π-electronic bridge has been investigated. Poly(methyl methacrylate) and different methacrylic copolymers as well as epoxy-amine oligomers with azo chromophores in the backbone or as side groups have been used as polymer matrices. The use of a polymer matrix containing carboxylic groups has resulted in significant decrease in the nonlinear-optical coefficient d33 as compared to the case of poly(methyl methacrylate) matrix with a guest chromophore content of 20 wt%. For materials with binary chromophores, d33 values of the studied materials have been higher than for conventional composites.

Dendronized Polymers with High FTC-chromophore Loading Density: Large Second-order Nonlinear Optical Effects, Good Temporal and Thermal Stability

In this study, two new dendronized nonlinear optical (NLO) polymers were synthesized with high FTC chromophore loading density by introduction of high generation chromophore dendrons on the side chains. Due to their suitable molecular weights, both of them possessed good solubility in common solvents. They also inherited the advantages of dendrimers (large NLO coefficient), especially for PG2 whose NLO coefficient d33 value was as high as 282 pm·V-1. Also, PG2 had a good temporal stability with 80% of its maximum value being retained at the temperature as high as 129 °C.

Dendronized azochromophores with aromatic and perfluoroaromatic fragments: Synthesis and properties demonstrating Ar[sbnd]ArF interactions

Syntheses of four new dendronized azochromophores were performed from 2-(2-amino-5-nitrophenoxy)ethanol, 2-[methyl(phenyl)amino]ethanol, 3,5-bis(benzyloxy)benzoic acid and 3,5-bis[(pentafluorophenyl)methoxy]benzoic acid using azo coupling reaction and ester formation reaction in presence of N,Nʹ-dicyclohexylcarbodiimide and 4-(dimethylamino)pyridine. Arene-perfluoroarene (ArArF) interactions are demonstrated in single crystal structure of dendronized azochromophore between pentafluorophenyl fragment and acceptor part of the azochromophore. The effect of ArArF interactions becomes apparent in thermal and nonlinear optical properties of the chromophores. Glass transition temperatures of synthesized azochromophores are in the range from 37 to 60 °C. Nonlinear optical properties of synthesized azochromophores were characterized by second harmonic intensity measurements in corona poled thin films of pure amorphous solids. Nonlinear optical coefficient d33 values for molecular glasses containing single azochromophore were in the range from 20.2 to 50.5 pm⋅V−1.

Study of novel nonlinear optical material based on Poly(aryl ether ketone) and its application in SHG imaging

Novel nonlinear optical polymer based on poly(aryl ether ketone) was designed and prepared. Such kind of materials showed excellent water solubility and thermal properties, its onset decomposition temperature can reach 314 °C; glass transition temperature can reach 170 °C. Though the nonlinear optical coefficients (d33) is not very large at 1310 nm, just about 13.9 pm/V; such kind of materials show us a low absorption spectral window at red and infrared light area (wavelength longer than 650 nm). Under the laser of 1310 nm, the morphology of the poled films can be detected by second harmonic generation (SHG) scanning microscopy.

Synthesis and characterization of novel polyhalogenaromatic polyimide material for electro-optic applications

New highly fluorinated aromatic polyimide based on 4-chloro-2,5,6-trifluoro-1,3-phenylenediamine and 2,2-bis(3′,4′-dicarboxyphenyl)hexafluoropropane dianhydride was prepared by the two methods condensation in a solution followed by a high-temperature solid-state chain extension and one-pot high temperature polycondensation in a benzoic acid melt. The polyimide is soluble in polar amide- and ketone-type solvents, has good thermal stability and a high glass transition temperature. The polyimide films exhibit a low cut-off wavelength and excellent transparency in the UV-vis-near IR range. Low molecular weight prepolymer, formed by the solution condensation, was used to obtain the guest-host electro-optic polymer having a high glass transition temperature. The prepolymer layer doped with azochromophore DR1 (25wt%) was subjected to a combined poling+curing procedure upon a two-stepped heating in a corona discharge field. Nonlinear optical coefficient d33 of the prepared chromophore-doped highly halogenated polyimide film measured by the Maker fringes method is 70pm/V at the fundamental wavelength of 1064nm and remains stable up to 85°C.

Quadratic nonlinear optical parameters of 7% MgO-doped LiNbO3 crystal

Pure and 7% MgO-doped lithium niobate (LiNbO3) single crystals were grown by the Czochralski technique. The shift of optical absorption edge in 7% MgO-doped crystal in direction of shorter wavelength compared to undoped crystal was observed. The second harmonic generation measurements of 7% MgO-doped LiNbO3 crystal were performed at room temperature by means of the rotational Maker fringe technique using Nd:YAG laser generating at 1064nm in picoseconds regime. Experimentally obtained value of nonlinear optical coefficient d33 for 7% MgO-doped LiNbO3 was found to be less than for undoped crystal but higher than for 5% MgO-doped. I-type phase-matched second harmonic generation was achieved and the value of phase-matched angle was calculated. High quadratic nonlinearity together with tolerance to intensive laser irradiation makes 7% MgO-doped LiNbO3 crystal interesting for application in optoelectronics.

Main Chain Dendronized Polymers: Design, Synthesis, and Application in the Second-Order Nonlinear Optical (NLO) Area

For the first time, two nonlinear optical (NLO) main chain dendronized polymers, MDPG1 and MDPG2, were prepared through the Suzuki coupling reaction by utilizing low-generation dendrimers as the monomers. These polymers inherit the advantages of both main chain polymers (which usually demonstrate good stability of the NLO effect) and dendronized polymers (which usually possess a large NLO coefficient) simultaneously. For MDPG2, its NLO coefficients d33 value and d33(∞) value are up to 116 and 20 pm/V, respectively, very similar to those of the normal dendronized polymer DPG2. Interestingly, thanks to its main chain structure, the onset temperature for the decay of its d33 value was tested to be 100 °C, 30 °C higher than that of DPG2.

Using low generation dendrimers as monomers to construct dendronized hyperbranched polymers with high nonlinear optical performance

By combining the structure of hyperbranched polymer and dendrimer, two second-order nonlinear optical (NLO) dendronized hyperbranched polymers, PG1 and PG2, were prepared with satisfactory yields through the Suzuki coupling reaction using low generation dendrimers as the monomers. Due to their highly branched structure, both of them have good solubility and processability. These two polymers inherited the advantages of hyperbranched polymers (good stability) and dendrimers (large NLO coefficient) simultaneously, especially for PG1. Its NLO coefficient d33 value and d33(∞) value were as high as 166 and 27 pm V−1, respectively, and no obvious decay was observed in its d33 value when its thin film was heated to 117 °C.

Six-branched chromophores with isolation groups: synthesis and enhanced optical nonlinearity

Three new six-branched chromophores with different isolation groups were designed and synthesized by incorporating azo chromophores onto phenyl glycerol ester via an esterification reaction. The chemical structures were confirmed by 1H NMR, 13C NMR, FT-IR spectroscopy, mass spectrometry, element analysis and UV-visible absorption spectra. The six-branched dendritic chromophores can form thin films directly without adding any polymer matrix and show a quite high chromophore loading density. After electric poling, the nonlinear optical coefficients (d33) of the dendrimer films were determined to be around 113, 142 and 136 pm V−1, which are almost 3 times the maximum d33 value of the azo-chromophore doped polymer films. The further improvement in optical nonlinearity was successfully realized by mixing the six-branched chromophores containing different isolation groups.

Nonlinear-optical properties of epoxyamine-based thin films

The nonlinear optical coefficients d33 of epoxyamine-based thin films containing 4-amino-4’-nitroazobenzene chromophore fragments in the main chain were measured by a second harmonic generation technique.

The Role of the Chromophore Size and Shape on the SHG Stability of PMMA Films with Embebbed NLO Active Macrocyclic Chromophores Based on a Cyclotetrasiloxane Scaffold

In this work, the second harmonic generation (SHG) and the nonlinear optical (NLO) coefficients d33 of PMMA films, containing 4 wt % NLO active macrocyclic chromophores based on a cyclotetrasiloxane scaffold and of their monomeric structurally homologous NLO active chromophores, were obtained by an electrical poling process and measured at room temperature during a period of many months, after switching off of the orienting electric field. The composite films based on the macrocyclic NLO chromophores have shown much higher d33 values and stability in the time if compared to films based on the monomeric structurally homologous NLO chromophores. Such higher stability in the time is related to a higher decay time τ2 and to a lower rotational diffusional coefficient DR, as a consequence of the increased size of the macrocyclic NLO chromophores. We have observed that also the shape of the NLO chromophores may play a role. A good stability in the time of the d33 values is maintained if the PMMA films, containin...

Terahertz Generation and Optical Properties of Lithium Ternary Chalcogenide Crystals

We have investigated the generation of THz radiation in lithium ternary compounds LiInSe2, LiGaSe2, LiInS2, LiGaS2 and characterized these materials by THz time-domain spectroscopy. Using 800 nm femtosecond excitation pulse, all crystals produce THz radiation due to an optical rectification corresponding to the nonlinear optical coefficient d33. We have measured refractive indices along the x-axis and the z-axis for all crystals in the range 150–700 μm and fitted them by using Sellmeier equation. With respect to the obtained results, velocity-matching between the incident laser pulse and the generated THz wave cannot be achieved at 800 nm, but for shorter wavelengths. Hence, an enhanced THz generation in Lithium ternary compounds may be observed by using a laser emitting below 800 nm.

Second harmonic generation and photochromic grating in guest-host polymer system containing azo amide chromophores

AbstractThe azo sulfonamide chromophores containing long aliphatic chain were used as active nonlinear optical (NLO) materials in films prepared by spin-coating on glass surfaces. The sulfonamides were: N-{4-[{4-[(pyrimidin-2-ylamino)sulfonyl]phenyl}diazenyl]phenyl} decanamide (Amid P); N-{4-[{4-[(1,3-thiazol-2-ylamino)-sulfonyl]phenyl}diazenyl]phenyl} decanamide (Amid T) and N-{4-[(4-nitrophenyl)-diazenyl]-phenyl}undec-10-enamide (Amid N). The host matrix was a copolymer of methyl and butyl methacrylate. The formation of diffraction grating by the guest-host system was successful only in the case of Amid N. The pitch and amplitude of the grating was 930 nm and ca. 45 nm, respectively. Quantum chemical calculations revealed that the chromophores were moderate NLO-fores showing static β values of ca. 110-130 m4/V. Two procedures were involved to align chromophores to determine first order NLO susceptibility: a) corona poling, and b) all-optical poling. The NLO coefficient d33 determined in corona poled film was 25.2, 28.6 and 93.2 pm/V for Amid P, T and N, respectively.

Strain-Induced Modulations of Electro-Optic and Nonlinear Optical Properties of ZnO: A First-Principles Study

Strain-dependent electro-optic constant r33 and nonlinear optical coefficient d33 of ZnO are investigated systematically using density-functional theory based linear-response perturbation method. Miscellaneous properties, such as dielectric constants, elastic constants, piezoelectric coefficients, nonlinear optical coefficients, and electro-optic constants of other II-VI compound semiconductors (both Wurtzite and Zinc-blende structures) are also calculated for comparison with the results of unstrained ZnO. Extensive first-principles calculations show that both r33 and d33 of ZnO decrease almost linearly with increasing strains, which indicates that appropriate compression along the [0001] direction of ZnO could enhance its electro-optic and nonlinear optical properties, while stretching may weaken the corresponding properties. Among the involved Wurtzite structures, ZnO has the highest elastic constant, piezoelectric coefficient and electro-optic constant, showing practical importance.

Enhanced Nonlinear Optical Activity of Molecules Containing Two D−π−A Chromophores Locked Parallel to Each Other

A series of H-shaped second-order nonlinear optical (NLO) chromophores with two parallel and nonconjugated D−π−A units have been synthesized, in which a 9,10-dihydroanthracene is employed as molecular backbone. The measurement results of hyper-Rayleigh scattering (HRS) and UV−vis spectra show that the first molecular hyperpolarizability (β) values of H-shaped chromophores are remarkably increased compared with the corresponding mono-D−π−A unit reference compounds (the enhancements per azo D−π−A unit from 1.2 to 3.0 are observed), without causing a large shift of the absorption band to longer wavelength. Therefore, it gives an available way of solving the trade-off between nonlinearity and transparency in designing NLO chromophores. Furthermore, some main-chain fluoro-containing polyimides embedded with the H-shaped chromophores have also been prepared. The elemental investigation results show that the polyimides exhibit a higher macroscopic nonlinear optical coefficient (d33 = 35.0 to ∼70.2 pm/V), good th...

Synthesis and Properties of Two Second‐Order Nonlinear Optical Polymers: an Attempt toward the Balance between Nonlinearity and Transparence against Intrinsic Trade‐off

AbstractTwo new poly(arylene ether sulfone)s (P1 and P2) with two new accepting group (TCF)‐based chromophores (1 and 2) in side chains, respectively, were designed and synthesized. The two chromophores contain the same electron donating group (dialkylamino group) and the same accepting group (TCF), but different conjugation bridges. Compound 2 contains a combined conjugation bridge (phenyl‐diazene plus styrene), but the bridge of 1 is much shorter (styrene only). A variety of optical properties were studied. Compared with P1, P2 exhibited comparable nonlinear optical coefficient (d33) and better transparency (the maximum absorption was blue‐shifted by 16 nm), though the conjugation bridge of chromophore 2 in P2 was much longer than that of 1 in P1. This result may help design nonlinear optical polymers achieving the balance between nonlinearity and transparence against the intrinsic trade‐off.

Synthesis and Properties of Polyimide-Based Optical Materials

Three types of polyimides (PIs) with different structures and fluorine contents were prepared via a simple two-step method. The PI precursors, poly(amid acid)s (PAAs), were first synthesized from ring-opening polyaddition, then, the PAA films were subjected to thermal imidization. The chemical and the optical properties of the polyimides were investigated and compared. The result showed that all of the polyimides had good thermal stability. The refractive index of the fluorinated polyimide was lower than that of the common polyimide and could be controlled by adjusting the fluorine content in the structure. The second-order nonlinear optical (NLO) coefficient (d33) for the PMDA/ODA polyimide (PMDA = pyromellitic dianhydride and ODA = 4,4’-diamino diphenyl ether) was 10.69 × 10−9 esu at 1064 nm and could be increased to 24.55 × 10−9 esu by doping with a small amount of perylene dianhydride. The optical loss for the PMDA/ODA film and for the 6FDA/ODA film were 0.326 dB/cm and 0.102 dB/cm respectively at 650 nm. Due to many attractive properties mentioned above, polyimide-based materials are expected to have potential applications in the field of organic optical waveguides.