Yasushi Ohe

A novel dry photopolymer for volume-phase holograms

A novel photopolymer for the fabrication of high-resolution volume-phase holograms, which primarily are used for holographic optical elements, is reported. This photopolymer consists of a thermosetting resin as a polymeric binder, a polyfunctional monomer, a photoinitiator, and a sensitizing dye. The chemistry to form images is based on the polymerization of an acrylic monomer initiated by radical species while making the holographic exposure, and accelerated diffusion transfer of the polymerized monomer with postexposure baking, and of a bisphenol-type epoxy resin as a binder initiated by cations with UV exposure, which are generated through photodecomposition of a diaryliodonium salt-sensitized 3-ketocoumarin dye. Exposure of these photopolymer films to an Ar+ laser beam emitting 514.5 nm light at 60–150 mJ/cm2 and subsequent heat treatment resulted in a refractive index alteration according to the light intensity. With this dry process, high diffraction efficiency and heat-stable holograms can be formed.

Application of a novel photopolymer to a holographic head‐up display

A novel photopolymer for fabrication of high-resolution volume holograms, which primarily are used on holographic optical elements such as head-up display (HUD), is reported. This photopolymer consists of bisphenol-type epoxy resin and radically polymerizable aliphatic monomer with diaryliodonium salt and 3-ketocoumarin (KCD) as a complex initiator. The chemistry of imaging formation is based on the radical polymerization of the monomer initiated by a holographic exposure, following by the cationic polymerization of epoxy resin by UV-exposure after post-exposure baking. The yellowish color of hologram derived from KCD, the shape of peak of reconstructed light and the blue shift of wavelength of reconstructed light, were improved in order to satisfy the specifications for the combiner of HUD. A stand type holographic HUD system as an example of automotive display attached on the dashboard of an automobile is demonstrated. The display gives a high contrast image, and the combiner has good durability. Copyright

Application of a photopolymer to a holographic reflector for reflective liquid-crystal displays

A photopolymer for fabrication of volume-type transmission holograms, which are used primarily on the holographic reflector for reflective LCDs, is reported. This photopolymer consists of bisphenol-type epoxy resin and an acrylic monomer with diaryliodonium salt and 3-ketocoumarin as a complex initiator. The chemistry of the imaging formation is based on the radical polymerization of the monomer initiated by a holographic exposure, followed by the cationic polymerization of epoxy resin by UV exposure after postexposure baking. The yellowish color of the hologram derivatives that resulted from the sensitizing dye and from the photospeed were improved to satisfy the specifications for the holographic reflector. The holographic reflector now gives brighter images.

Highly sensitive positive resists for holography

New visibile llight sensitive positive type resists have been developed. The chemistry is based on the hydrolysis of polymers catalyzed by acid which is generated on sensitized photodecomposition of diphenyliodonium (DPI) salt. Dimethoxybenzhydryl methacrylate (DMOBHMA)-phenyl methacrylate (PhMA) copolymer was the best acid sensitive polymer tested, producing photoresists with sensitivity to an argon ion laser light and good holographic properties.