Xuchun Liu

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.

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.

Collisionless shockwaves formed by counter-streaming laser-produced plasmas

The interaction between two counter-streaming laser-produced plasmas is investigated using the high-power Shenguang II laser facility. The shockwaves observed in our experiment are believed to be excited by collisionless mechanisms. The dimensionless parameters calculated with the results suggest that it is possible to scale the observation to the supernova remnants using transformation and similarity criteria.

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)

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.

Application of all-optical poling in reversible optical storage in azopolymer films

Abstract Employing all-optical poling technique, we propose a novel method for optical storage based on the mechanism of orientational hole burning and photoinduced molecular reorientation of azobenzene. Recording of an optical binary image was experimentally demonstrated. The recorded information can be stored for a long time and also can be erased rapidly with a circularly polarized light. Furthermore, wavelength conversion of optical image is obtainable using such method. The storage characteristics of two different polymer systems, azo-doped poly(methyl methacrylate) (PMMA) and azo-functionalized polyimide (PI), were investigated and compared.

Poly(p‐diethynylbenzene) Derivatives for Nonlinear Optics

In this Letter, we report the growth of carbon nanofibers arrays by chemical vapor deposition in the presence of magnetic force. We find that when a magnet is applied carbon nanofibers arrays are grown and when the magnet is absent carbon nanotubes arrays are grown at the same experimental conditions. The nanofibers are worse in alignment and less in graphitization than those of the nanotubes grown at the same conditions. What is interesting is that two or three nanofibers can be connected together through a catalyst nanoparticle. These connections might be useful, especially in the fabrication of nanoelectronic devices

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.