Yuquan Shen

Photoinduced permanent gratings inside bulk azodye-doped polymers by the coherent field of a femtosecond laser

Permanent holographic gratings were fabricated in bulk azodye-doped polymethylmethacrylate by the coherent field of a femtosecond laser. Optical microscopy and atomic force microscopy observations revealed that the gratings consist of two parts, surface relief gratings on both surfaces and refractive index modulated volume gratings in the interior of the polymers. The diffraction efficiency of the first-order Bragg for the gratings was estimated to be 90%.

Modulated conjugation as a means of improving the intrinsic hyperpolarizability.

A new strategy for optimizing the first hyperpolarizability based on the concept of a modulated conjugated path in linear molecules is investigated. A series of seven novel chromophores with different types of conjugated paths were synthesized and characterized. Hyper-Rayleigh scattering experiments confirmed that modulated conjugation paths that include benzene, thiophene, and/or thiazole rings in combination with azo and/or ethenyl linkages between dihydroxyethylamino donor groups and various acceptor groups result in enhanced intrinsic hyperpolarizabilities that exceed the long-standing apparent limit for two of the chromophores. The experimental results are analyzed and interpreted in the context of quantum limits, which show that conjugation modulation of the bridge in donor/acceptor molecules simultaneously optimizes the transition moments and the energy-level spacing.

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. ...

The fabrication of permanent holographic gratings in bulk polymer medium by a femtosecond laser

Refractive-index-modulated holographic gratings have been recorded for the first time in the interior of polymer bulk, by a femtosecond laser at 800 nm. The polymer bulk was prepared by doping an azo dye, HPNA in polymethylmethacrylate. This sample preparation process is quite simple. Multi-photon absorption and, as a result, photoinduced changes in isomer population were postulated as a brief discussion on the mechanism of the grating formation.

Dynamic studies of degenerate four‐wave‐mixing in an azobenzene‐doped polymer film with an optical pump

Degenerate four‐wave‐mixing was performed in azobenzene‐doped polymethyl methacrylate film under a low power continuous‐wave laser at 632.8 nm with a pulsed pump laser of 532 nm. Different temporal profiles of the degenerate four‐wave‐mixing signal were observed under different pump energies, which originated from the relaxation processes between the energy levels of azobenzene during the photoisomerization, especially the transferring processes between the triplet states of the two isomers, trans and cis.

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.

Study on the thermal properties of doped PMMA systems

The thermal optical coefficient (TOC) and volume thermal expansion coefficient (TEC or β) of poly(methyl methacrylate) (PMMA) polymers doped with azobenzene dyes were investigated. A novel approach for determining the TEC has been suggested and a non-linear variation in the TOC with increasing wt% of the dopant has been observed and tentatively explained. In addition, the refractive index (RI) contrast necessary for forming a waveguide was demonstrated to be easily achievable by adding a higher-refractive-index material to the blank polymer. Copyright

Holographic recording and light amplification in doped polymer film.

We reported an experimental study of holographic recording and signal light amplification through higherorder diffracted waves from holographic gratings recorded in an acceptor-donor-substituted azobenzene-doped poly(methyl methacrylate) thin film.

Low-power phase conjugation in push–pull azobenzene compounds

Push-pull azobenzene compounds were synthesized by the diazocoupling reaction, and low-power phase conjugation of azobenzene-compound-doped poly(methyl methacrylate) films was studied with a He-Ne laser at 632.8 nm. It is shown that this kind of polymer has appreciable third-order optical nonlinearity, with a chi((3)) of approximately 10(-4) esu in the tail of absorption.

Magnesium Ethoxide as an Effective Catalyst in the Synthesis of Dicayanomethylendihydrofurans

Abstract Magnesium ethoxide was used for the first time in the synthesis of the titled compounds. In these preparations, product yields were significantly improved compared with similar synthesis catalyzed by other metal ethoxides. The effectiveness of magnesium ethoxide as catalyst was tentatively rationalized.