Jianfeng Zhai

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%.

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.

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

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.

Phase-matched second-harmonic generation in bulk azodye-doped polymers by all-optical poling

We demonstrate phase-matched second-harmonic generation (SHG) in bulk azodye-doped polymethylmethacrylate using an all-optical poling technique. During the seeding process, samples were irradiated simultaneously by coherent superposition of the fundamental and the second-harmonic light of a nanosecond laser. The measurements for the dependence of SHG on the sample thickness show that the SHG signals increase with the increase in thickness of the samples, indicating that a χ(2) grating that satisfies the phase-matching condition for SHG could be optically induced in the polymer samples.

Synthesis and characterization of a novel styrylthiophene monomer and corresponding heterocyclic polymer for NLO materials

A novel (Trans)-7-[4-N,N-di-((beta) -hydroxyethylamino benzene)] ethenyl 3,5-dinitrothiophene(HBDT) monomer was synthesized and characterized. We also present in this paper an approach to synthesized processible, un-cross-linkable, and thermally stable heterocyclic polymer (Polyurethane) with the monomer covalently incorporated. The details of synthesizing the monomer and un-cross-linked heterocyclic polymer are presented. The un-cross-linked polymer exhibited good solubility in common organic solvents, permitting processing relevant to device fabrication. After being efficiently poled and cured, optical-quality films exhibited moderate nonlinearity and thermal stability.