Daniel James Mickish

Hologram recording in du Pont's new photopolymer materials

New families of transmission and reflection holographic photopolymer materials and their performance are described. The materials are composed of polymeric binders, monomers, initiation system, and sensitizing dyes. The physical and holographic properties may be controlled by choice of components. Photopolymerization and diffusion of monomers is the proposed mechanism for recording of refractive index modulation. The materials are sensitized from the Uv to the red with typical exposure energies form 10 to 100 mJ/cm2. Hologram recording consists of exposure, UV cure, and heat processing. Significant refractive index modulation occurs during exposure. Processed holograms are insensitive to humidity and temperature. Holographic properties and performance of various formulations are discussed, as well as applications of these materials.

Effects of interfacial polarization and loading factor in dielectric‐loss measurements of composites

The effect of the loading factor (the ratio of the conductive volume to the total volume) of a composite can lead to errors of 20% if not considered when interpreting dielectric‐loss measurements. Free‐carrier interfacial polarization is shown to be unimportant in the interpretation of the Maxwell‐Wagner effect for certain classes of composites contrary to currently accepted thought, whereas it can be important in the interpretation of the Dember effect for the same materials. Non‐Debye loss in cases where free‐carrier interfacial polarization is unimportant is shown to be caused by an additional frequency‐dependent component of the conductivity, e.g., that caused by dipole reorientation or conformational rearrangement.

Determination of x-ray phosphor scintillation spectra

A fast, unique method for determining phosphor scintillation spectra by means of an electronic apparatus is described. A major advantage is that all of the controls are digital. This includes coincidence timing to determine whether an x-ray absorption event has occurred as well as control of the time window during which the number of light photons emitted in response to an x-ray absorption event is counted, and storage of the photon count itself. The apparatus and its logic are described in detail. The scintillation spectra and the resulting calculated Swank coefficient values of several phosphors obtained with this apparatus are presented as examples.