Richard T. Ingwall

Cationic ring-opening photopolymerimization methods for volume hologram recording

A new photopolymer holographic recording material based on cationic ring-opening polymerization avoids limitations of conventional holographic photopolymers resulting from the free radical chemistry typically employed. The effects of oxygen, moisture, and component characteristics on holographic recording characteristics are described. Sensitivities greater than 0.1 cm2/mJ and refractive index modulations greater than 5 X 10-3 are achievable with negligible changes in the physical dimensions (volume change as low as 0.4%) of the imaged material. Linear recording is observed for exposure fluence up to 20 mJ/cm2. Good Bragg selectivity consistent with the imaged thickness is observed, and both the angular response and the diffraction efficiency are stable in these materials without the need for post-imaging fixing procedures.

Mechanism Of Hologram Formation In DMP-128 Photopolymer

Electron micrographs of volume phase holograms recorded in DMP-128 reveal microstructure that is responsible for holographic activity. Solid and porous layers alternate with a spacing commensurate with the recorded fringe pattern. The difference in material density between the solid and porous regions accounts for the refractive index modulation and therefore the holographic activity of DMP-128 holograms. The pores of the holograms are interconnected and can be filled with many low and moderate viscosity liquids. Diffraction efficiency, bandwidth, and wavelength of maximum efficiency are profoundly and predictably affected by filling the hologram pores.

Hologram: liquid-crystal composites

We describe the formation and selected properties of composites made from DMP-128 transmission holograms and the nematic liquid crystal E7. Analysis of the liquid crystal structure in the composites by polarizing microscopy, refractive index measurements, and differential scanning calorimetry produced two primary observations. (1) Treatment of the interior surface of the porous holograms controls the nature of the liquid crystal alignment; both planar and homeotropic alignment is possible for the E7 composites. (2) Incorporation of E7 into DMP composites significantly reduces its degree of order compared to that for a standard nematic cell.

Fabrication and properties of composite holograms recorded in DMP-128 photopolymer

Special features of the photopolymer system DMP128 can be exploited to form composites comprising a supporting matrix derived from the photopolymer and a dispersed second phase. Examples of two composite types are described here; composites with a nematic liquid crystal and composites used as waveguides. The diffraction efficiency of holograms containing the liquid crystal can be rapidly changed by applying an electric field. Periodic structures can easily be incorporated in the waveguide composites.

Control of Chromophore Length in Electroluminescent Polymers. Part II. Mainchain Polymers

Abstract Electroluminescence emission has been demonstrated in mainchain polyesters and a structurally analogous polyamide. High molecular weight polyesters were synthesized by condensation of a dihydroxy functionalized, substituted, phenylene vinylene analogue, e.g., the lumo-phore, with a variety of dicarboxylic acid chlorides. The structure and hence the conjugation length of the emitting comonomer was predetermined prior to polymerization. Since the diacid moieties did not contribute to the conjugation length and hence the emission wavelength, the structure of the diacid was determined on the basis of its ease of synthesis, reactivity, and solubilizing ability in the final polymer. In each of the polyesters the electroluminescence wavelength of light-emitting diodes made from these polymers was similar to their photoluminescence emission spectrum in solution and the solid state at room temperature. The emission wavelengths ranged from blue to green. The polyamide exhibits a very broad band, nearly whi...