Qiguang Yang

Third-order optical nonlinearity of the carbon nanotubes

Third-order optical nonlinearity of the carbon nanotubes was investigated with both 30-ps-wide and 8-ns-wide Nd:YAG laser beams. Both 1064 and 532 nm were used in each case. The nonlinear optical temporal response was obtained both on the picosecond scale and on the nanosecond scale, and the corresponding mechanism is discussed. Finally, we have compared the average contribution of one carbon atom to the third-order optical nonlinearity in the carbon nanotubes with that in C60, finding some enhancement of the third-order optical nonlinearity in the carbon nanotubes.

Third-order optical nonlinearities of near-infrared dyes

Near-infrared dyes - di- and tri-indocarbocyanine dyes and nickel dithiolenes - were synthesized and their third-order optical nonlinearities in solutions were investigated by using the degenerate four-wave mixing technique. Large third-order nonlinear optical susceptibilities with gamma values of up to 10(-29) esu were observed. The gamma value of the indocarbocyanine dyes increases with increase of conjugation length of the polymethine chain. The central ring structure in the chromophore lowers the gamma value of the indocarbocyanine dyes. With change of the substituents on the benzene ring an increase in gamma value is observed for all the asymmetric nickel dithiolenes. The order of increase of nonlinear hyperpolarizability is as follows: H < Cl < CH3 < C2H5 < CH(CH3)(2)

Excited-state enhancement of the third-order optical nonlinearity of a square planar complex

Abstract Excited-state enhancement of the third-order nonlinear optical susceptibility of a square planar complex, (2,2′-bipyridine)Pt(1,2-dicyano-1,2-ethylene-dithiolate), was observed when the sample was optically pumped by either a picosecond or a nanosecond pump beam of 355 nm wavelength. For the picosecond case, the temporal behavior of the enhancement was investigated, and found to be characterized by a slow and a fast components, which are attributed to populations of the first excited state S 1 and the second excited state S 2 , respectively. For the nanosecond case, the enhancement of the nonlinearity is attributed predominantly to the population of the first excited state S 1 . The molecular hyperpolariabilities of the S 1 state and the S 2 state, γ S1 and, γ S2 , were determined to be 1.9 × 10 −31 and 1.0 × 10 −30 esu, respectively, which are much larger than the γ 8 of the ground state ( γ g −33 esu).

All-optical poling of a polyimide film with azobenzene chromophore

Abstract Permanent all-optical poling of a side-chain polyimide film with azobenzene chromophore using a low power nanosecond laser was experimentally demonstrated. The characteristic kinetics of growth and decay of the induced second-order susceptibility were measured by second-harmonic generation. The second-order nonlinear optical coefficient d33 was determined to be 2.6 pm/V, and was observed to be stable at 85°C.

Permanent optical poling in polyurethane via thermal crosslinking

Abstract Permanent optical poling was achieved in a crosslinkable system, a polyurethane with disperse red 19. Thermal stability of light-induced second order susceptibility was investigated for samples poled at different temperatures. The induced susceptibility d33 of the sample poled at 85°C was measured to be 46 pm/V, and could be stable at that poling temperature. Experimentally, it was demonstrated that the chemical crosslinking of the polymer matrix in optical poling procedures resulted in good stability of polar orientation of the nonlinear optical chromophores.

π-Conjugated soluble nickel-polyyne copolymer : Synthesis and third-order optical nonlinearity

By means of homogeneous stepwise condensation method, both the Ni-polyyne copolymers with PPh 3 and PBu 3 ligands, and modified π-conjugated nickel-containing copolymers have been synthesized and confirmed by infrared (IR) analysis. The Ni-polyyne copolymers obtained are yellow powder having a M w of about 1 ∼ 2 x 10 4 and a molecular weight distribution (MWD) of less than 3, and they are soluble in tetrahydrofuran (THF), CHCl 3 , and toluene. Their third-order nonlinear optical properties have been investigated by a degenerate four-wave mixing (DFWM) technique. The effect of the nature of the ligands attached to the nickel atoms, the structure, and the length of π-conjugation between the 2 metal centers in the main chain on the hyperpolarizability γ of the Ni-polyyne polymers have been discussed. The maximum susceptibility x (3) and hyperpolarizability γ of the Ni-polyyne polymers reach 5.17 x 10 12 and 2.30 x 10 30 esu, respectively.

Dynamic studies of charge-separated-state enhancement of the optical nonlinearity of a porphyrin heterodimer

Light‐induced enhancement of the third‐order nonlinear optical susceptibility of a heterodimer consisting of two different porphyrin monomers, a zinctetra(4‐sulfonatophenyl)porphyrin and a zinctetra(4‐N‐methyl‐pyridyl)porphyrin, was observed when the sample was optically pumped by a 30 ps, 532 nm pump pulse. The temporal behavior of the enhancement was studied. It was found that the enhancement was due predominantly to the population of the charge‐separated state with a large electronic third‐order nonlinear optical susceptibility

Nonlinear Optical Properties of Some New Conjugated Copolymers

The ground- and the excited-state nonlinearities of two new copolymers are investigated in nanosecond scale at 1064 nm. It is found that the excited-state susceptibility is dramatically larger than the corresponding ground-state susceptibility for each sample. The experimental results also give evidence that superlattice structure of the copolymers can enhance, especially for the excited state, the molecular hyperpolarizabilities significantly. This enhancement may be attributed to the confinement effect of the pump-induced carriers.

Photoinduced electron transfer and dynamic behavior of charge-separated state nonlinear optical process in a self-assembled porphyrin supramolecular system

Abstract The spectroscopic properties of a supramolecular system consisting of two oppositely charged porphyrin monomers, zinc tetra(4-sulfonoatophenyl)porphyrin and zinc tetra(N-methylpyridyl)porphyrin were studied by absorption and fluorescence spectroscopy. The stoichiometry of the self-assembled porphyrins were determined by a fluorimetric titration method showing the formation of the 1:1 heterodimer. Photoinduced electron transfer and charge separation in the supramolecular system have been studied by time resolved forward degenerate-four-wave-mixing (DFWM) geometry. The results indicated the formation of the charge-separated state within 30 ps and the recombination time is about 340 ps. Light-induced enhancement of third-order nonlinear optical (NLO) susceptibility was observed.

All-optical poling of several different molecular-design films with azobenzene chromophore

Four different molecule-design films with azobenzene chromophore were investigated in our experiment, which were the guest-host system, the side-chain system, the crosslinked system and the diazo side-chain system. The decaying processes of them were presented and compared in pair. The differences between them were explained with respect to their different molecule design.