Large Third-order Nonlinear Optical Response Research Articles

Theoretical study on the spectroscopic and third-order nonlinear optical properties of two-dimensional charge-transfer pyrazine derivatives

ABSTRACTIn this paper, density functional theory method was employed to study the electronic absorption spectrum and electronic static second hyperpolarisability of X-shaped pyrazine derivatives with two-dimensional charge-transfer structures. Computational results show that the push–pull electron abilities of the substituent groups and the length of the conjugated chains affect the electronic spectrum and static second hyperpolarisability of the pyrazine derivatives. As the push–pull electron abilities of the substituent groups or the length of the conjugated chains increases, the frontier molecular orbital energy gap decreases, resulting in increased second hyperpolarisability and redshift of the electronic absorption bands. The electronic absorption spectra of the pyrazine derivatives maintain good transparency in the blue light band. The electronic static second hyperpolarisability exhibits a linear relationship to the frontier molecular orbital energy gap. Particularly, increasing/decreasing the push–pull electron abilities of the substituent groups considerably affect the static second hyperpolarisability in long conjugated systems, which is important to the modulation of molecular organic nonlinear optical (NLO) properties. The studied pyrazine derivatives show large third-order NLO response and good transparency in the blue light band and are thus promising candidates as NLO materials for photonics applications.

Large third-order nonlinear optical response of porphyrin J-aggregates oriented in self-assembled thin films

The preparation and characterization of a self-assembled material showing a high nonlinear response and good photostability to ultrashort laser pulses is presented. The material is built by alternate deposition of tetrakis(4-sulfonatophenyl)porphyrin diacid (H4TPPS2−) and poly(diallyldimethylammonium chloride) (PDDA) forming electrostatically self-assembled multilayers (ESAMs). UV-visible absorption and emission experiments show that in this matrix H4TPPS2− is present mainly in its J-aggregated form. Furthermore, linear dichroism experiments on a 3 bilayer film show a preferential alignment of the porphyrin aggregate with the J-band transition dipole moment parallel to the film surface. The two photon absorption (TPA) properties of these films are investigated with the Z-scan technique at 806 nm, employing 130 fs pulses. The samples exhibit strong nonlinearities with a very large two-photon absorption coefficient βTPA of 50 cm GW−1. The origin of this large response is investigated. It has been already demonstrated that aggregation enhances the molecular TPA cross section of H4TPPS2− from 30 to 1000 GM in water solution thanks to cooperative effects. In a 20 bilayer film a further increase by a factor of 1.7 is observed and explained in terms of preferential alignment of J-aggregates in the multilayers.

Core-Modified Expanded Porphyrins with Large Third-Order Nonlinear Optical Response

The third-order nonlinear optical response through measurement of two-photon absorption cross-sections (TPACS) for aromatic core-modified expanded porphyrin analogues by a femtosecond open aperture Z-scan method is reported. The values reported here are among the largest known so far in the literature for any organic molecules.

Bismuth manganite: A multiferroic with a large nonlinear optical response

We report evidence for ferroelectricity in bismuth manganite epitaxial films from optical second-harmonic generation (SHG). The change in the polar symmetry of SHG signals under external electric fields is correlated to specific changes in the ferroelectric domain microstructures. We also observe giant enhancement of SHG by 3 to 4 orders of magnitude with effective ${d}_{f}\ensuremath{\sim}193\mathrm{p}\mathrm{m}/\mathrm{V}$ under electric fields of \ensuremath{\sim}707 V/mm. The material also exhibits a large third-order nonlinear optical response with nonlinear absorption coefficient ${\ensuremath{\alpha}}_{I}\ensuremath{\sim}\ensuremath{-}0.08\mathrm{c}\mathrm{m}/\mathrm{k}\mathrm{W}$ and nonlinear refractive index ${n}_{I}\ensuremath{\sim}\ensuremath{-}0.53\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}{\mathrm{cm}}^{2}/\mathrm{W}.$

Wavelength dependence of ultrafast and large third-order non-linear optical response of polyacetylene nanoparticles

The third-order optical non-linearity was measured in nanopolyacetylene using femtosecond optical Kerr effect technique at wavelength from 790 to 860 nm. The ultrafast non-resonant effective second-order hyperpolarizibility for single polyacetylene nanoparticle was estimated to be as large as 1.0×10 −27 esu, which corresponding to the γ c of single carbon atom contribution equals to 5.0×10 −33 esu. We ascribed the observations to the highly ordered structure of nanopolyacetylene and delocalization of the π electrons along the conjugated chains was supposed to be responsible for such properties.

Large third-order nonlinear optical response of conjugated copolymers consisting of fluorene and carbazole units

Off-resonant third-order nonlinear optical properties using degenerate four-wave mixing measurements in solution at 1064 nm have been studied for novel π-conjugated, processible, optically transparent and thermally stable copolymers constituted of carbazole and fluorene. The second-order hyperpolarizability γ 1111 per repeat unit of the polymer containing alkyne segment (Cz-PFE) is as high as 6.5×10 −31 esu. The large nonlinearity of Cz-PFE is attributed to its rigid planar and intrachain charge transfer structure.

Large third-order nonlinear optical response of a conjugated copolymer consisting of 2,5-diethynylthiophene and carbazole units

The third-order nonlinear optical (NLO) properties of a novel π-conjugated copolymer constituted of electron-rich carbazole and 2,5-diethynylthiophene have been studied using degenerate four-wave mixing (DFWM) at 1064 nm. The off-resonance second-order hyperpolarizability γ per repeated unit is estimated to be 2.2×10 −31 esu; the nonresonant third-order susceptibility χ (3) approaches (8.6±1.7)×10 −10 esu. The large ultrafast nonlinearity originates from an instantaneous electronic polarization.

Two-photon resonance enhanced nonlinear optical response in C 60-copolymer charge transfer complex

Ultrafast third-order nonlinearity of C 60-poly tetrahydrofurfuryl methacrylate charge transfer complex was measured using femtosecond optical Kerr gate at both 640 nm and 820 nm wavelength. In the material's two-photon absorption region, extra large third-order nonlinear optical response was observed.

Large third‐order nonlinear optical response from molecules with effective multidirectional charge‐transfer transitions: New design of third‐order nonlinear chromophores

Enhanced values of the second molecular hyperpolarizability, γ, are reported for molecules that undergo significant multidirectional charge redistributions between the ground and excited states, e.g., charge is displaced from the periphery to the center, or vice versa, upon excitation, in during large changes in electric moments higher than dipole moments. The γ‐values are compared with those for polyene‐like molecules having a similar number of π‐electrons. It is demonstrated that the “periphery‐to‐center charge‐transfer” design concept is fruitful and should lead to new molecules with high γ‐values.