James M. Hoover

Second‐order nonlinear optical measurements in guest‐host and side‐chain polymers

The second harmonic generation (SHG) coefficients dij of several corona‐poled guest‐host and side‐chain polymers have been measured and studied over time using a new Maker Fringe analysis. The electro‐optic coefficient r33 and scattering losses have also been measured in thin‐film waveguides, on silicon and glass substrates, made from some of the polymers. Kleinman symmetry (d15=d31) was not valid for near‐resonant SHG in these materials and d15/d31 was determined. Stable values of d33, for a fundamental of 1.064 μm, were as high as 40 pm/V for one of the side‐chain polymers. Optical waveguide losses determined from scattering measurements were as low as 0.4 dB/cm at 1.06 μm.

Second-order nonlinear optical properties of poled coumaromethacrylate copolymers

Second-order nonlinear optical properties of newly designed and synthesized coumaromethacrylate side-chain polymers are reported. The optimum poling conditions were determined experimentally. The optimum poling temperature for these side-chain polymers is well above the glass transition temperature. The second harmonic coefficient of films poled by coronaonset at elevated temperature and the linear electro-optic coefficient of films poled by contact electrodes were measured. The stabilized value of the second harmonic coefficient, d33, at 1064nm fundamental wavelength was found to be 13 pm/V. The linear electro-optic coefficient, r33, exhibits strong dispersion ranging from 2 to 12pm/V in the wavelength range 477 to 1115 nm.

New syndioregic main-chain, nonlinear optical polymers, and their ellipsometric characterization

New nonlinear optical polymers (NLOP) having potential utility in waveguides for the modulation and switching of optical signals are reported. A new class of chromophoric polymers which assume a folded, polar conformation of the backbone have been prepared. The polymers have a syndioregic arrangement of chromophores within the backbone (i.e., a head-to-head, tail-to-tail configuration). Polymers were synthesized by the polymerization of difunctional, precoupled pairs of chromophores and difunctional, bridging groups. Glassy, noncentrosymmetric films were prepared by electric field poling and by Langmuir-Blodgett (LB) deposition. Characterization of multilayer LB films by null ellipsometry to determine the anisotropic refractive parameters was performed at different angles of incidence and at a wavelength of 1.0 (mu).

New class of mainchain chromophoric nonlinear optical polymers

Head-to-tail mainchain chromophoric polymers have been of interest because of their high chromophore densities [about 30 X 1021 chromophores/cm3 in the case of poly(4-N-ethylene-N-ethylamino)-(alpha) -cyanocinnamate], their proposed tendency to align in an electric field more readily than unconnected chromophores, and the proposed enhancement of the macroscopic hyperpolarizability coefficients. These proposed properties have yet to be proven for the solid state. In fact, results on mainchain nonlinear optical polymers indicate that a much lower degree of alignment resulted than would be expected for unconnected dipoles. It is possible that the head-to-tail configuration of mainchain polymers has too high of an energy barrier to rotation and alignment to allow proper alignment of the dipoles. Therefore, a new class of mainchain polymers, namely head-to-head polymers connected with various flexible spacers (which may allow the dipoles to align) was developed. The synthesis and characterization of these new materials is described. The nonlinear optical properties of several of this new class of mainchain nonlinear optical polymers were compared to the properties of the head-to-tail mainchain polymers.

Organic polymeric materials for nonlinear optics: oligopeptide-bound chromophores in β-sheets

The synthesis and preliminary characterization of new polypeptide-bound chromophores are reported. These polymers were made for the purpose of assembling (beta) -sheets at an air- water surface, and processing them into nonlinear optical films by Langmuir-Blodgett (LB) deposition. These films should be amenable to integration on semiconductor wafers, e.g., as active optical waveguides for phase shifting.

Recent Synthetic Developments in Mainchain Chromophoric Nonlinear Optical Polymers

When the chromophores (dipoles) of a polymer are oriented electrically (electric field poling) and mobility is frozen below the glass transition temperature of the polymer, these materials can be used as frequency doublers (second harmonic generation (SHG)), and materials for waveguides and electro-optical devices.1