Peixian Ye

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.

Observations on the coupling channel of two mutually incoherent beams without internal reflection in BaTiO3

Abstract A new scheme of mutually-pumped phase conjugator that works not relying on the internal reflection has been demonstrated experimentally in both one BaTiO 3 crystal and two separated BaTiO 3 crystals. These new phase conjugators differ from the well known double phase-conjugate mirror in that a channel coupling two incident beams has been observed and shared photorefractive holograms with two or more interaction regions in the crystal have to be formed. Thus, it is also demonstrated that coupling channels of two incident beams can be formed not only with internal reflections inside the crystal but also without internal reflection.

Self‐pumped phase conjugation with a new mechanism in KTa1−xNbxO3:Fe crystals

A new model is proposed to explain the origin of the self‐pumped phase conjugation (SPPC) that we have observed in KTa1−xNbxO3:Fe crystals. In this model SPPC is generated by both four‐wave mixing and backscattering processes rather than by only one of them. The advantage of this kind of phase conjugator is also discussed.

Optical poling and its application in optical storage of a polyimide film with high glass transition temperature

The temperature dependence of optical poling of a side-chain azobenzene–polyimide film with high glass transition temperature was experimentally investigated. With the increase of the sample temperature the light-induced second-harmonic generation increased first, and then decreased as the temperature was near its glass transition temperature. The light-induced second-order nonlinear optical coefficient d33 for the optimum temperature was determined to be 6.9 pm/V, which was about 2.7 times that obtained at room temperature. Compared with optical poling at room temperature, this thermal-assisted optical poling not only enhanced d33 of the polyimide film, but also improved the polar order stability of molecules. Optical storage based on optical poling was also demonstrated experimentally.

Comparison of the temperature dependence of optical poling between guest-host and side-chain polymer films

A comparison of temperature-dependent optical poling between two azopolymers, a side-chain polymer system (disperse red 19-functionalized polyimide polymer) and a guest-host polymer (dispersed red 1-doped polymethyl methacrylate), has been performed at various poling temperatures ranging from 25 to 70 °C. The observed saturation levels of induced second-order nonlinear susceptibility in all cases could be resolved into two components with a faster and a slower decay process after poling, which were respectively attributed to the cis-to-trans isomerization and the loss of induced polar order by orientational diffusion of azo chromophores. The saturation level and its slower decay component were observed to increase with the increase of poling temperature in the side-chain polymer, but to decrease in the guest-host system. The faster decay components were observed to decrease with poling temperature in both the systems. The decay times of the faster component decreased with temperature in the two polymers. ...

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

Abstract 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.

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)

PHOTOREFRACTIVE PROPERTIES AND SELF-PUMPED PHASE CONJUGATION OF TETRAGONAL FE-DOPED KTA1-XNBXO3 CRYSTAL

This letter reports the two‐wave mixing experimental results of tetragonal Fe‐doped KTa1−xNbxO3. A 7.3 cm−1 gain coefficient and 42% diffraction efficiency have been obtained. For the first time internally self‐pumped phase conjugation is being observed in this crystal. At room temperature, the conjugate reflectivity measured is 21%.

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

Abstract 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.

Studies of shallow levels in undoped and rhodium-doped barium titanate

Spectral and temporal characteristics of light-induced absorption for an undoped and a Rh-doped as-grown BaTiO3 crystal were investigated and compared. Two dark-decay time constants corresponding to two shallow levels were observed: 40 ms and 1.2 s for undoped BaTiO3 and 39 ms and 3.4 s for Rh-doped BaTiO3. The light-induced absorption spectra were resolved into two components according to the dark-decay time constants. The resolved spectra reveal that one shallow level in Rh-doped BaTiO3 and one in undoped BaTiO3 are caused by a same impurity defect. The thermal activation energies of these levels were determined to be 0.53 and 0.7 eV for undoped BaTiO3 and 0.57 and 0.8 eV for Rh-doped BaTiO3. The 0.8-eV shallow level in BaTiO3:Rh is caused by Rh4+/5+; the other level, 0.57 eV, is the one that has the same defect origin as the 0.53 eV level in undoped BaTiO3. Other parameters for the shallow levels are also given.