Abstract: A process for hardening gelatin holograms after dehydration involving subjecting the hologram to an atmosphere containing aldehyde vapor and water vapor. The process provides hardening of the gelatin hologram to increase resistance to moisture and heat without adversely affecting diffraction efficiency. Monitoring of the diffraction efficiency during the aldehyde-water vapor treatment allows fine tuning of the hologram efficiency and evenness.

Abstract: A vehicle wheel cover is provided with a reflection-type hologram assembly having multiple exposure images therein. The sun or an artificial light source illuminates the hologram assembly as it rotates as a result of the vehicle moving. The exposure images are successively reconstructed to produce a single image that may be remotely positioned from and stationary relative to the rotating wheel cover.

Abstract: A layer of material having relatively low light sensitivity is interposed between a substrate and a light sensitive recording medium during recording of a slant fringe hologram. The layer frees the ends of the fringes from the substrate to permit greater expansion during a subsequent chemical swelling process, thereby resulting in a slant fringe hologram having improved efficiency. In one embodiment, a separate layer of light insensitive material is applied to the substrate prior to application of the recording medium. In another embodiment, a separate layer of light sensitive material is applied to the substrate and is then desensitized by exposure to incoherent light or by heat treatment prior to application of the recording medium.

Abstract: A method of manufacturing optical elements, such as for head-up displays, from holographically recorded interference patterns in a dichromatic gelatin is disclosed. The exposed hologram pattern is developed through hydration, the hydrated hologram gelatin is dehydrated by contacting the hydrated gelatin with a mixture of isopropyl alcohol and an inert anhydrous fluid, such as a liquid fluorinated hydrocarbon solution. The dehydrated hologram pattern can then be subsequently stabilized, for example, by baking.

Abstract: A method of developing a holographically recorded interference pattern in a dichromatic gelatin structure is provided. The process includes developing the hologram pattern by hydration and dehydration, baking the developed hologram pattern at a temperature equal or above 120.degree. C. for approximately 24 hours, rehydrating the developed hologram and dehydrating the developed hologram at a temperature of approximately 60.degree. C. for approximately 48 hours until the design wavelength response is attained to provide a stabilized hologram.

Abstract: A holographic recording medium is treated to reduce or eliminate unwanted extraneous diffraction and flare. Regions adjacent surfaces of the medium are desensitized to reduce contrast in the holographic fringe pattern along the surfaces, thereby eliminating planar phase grating effects. Treatments include applying a burst of gas or vapor to the surfaces of the medium, irradiating the surfaces with highly absorbed incoherent light, thermally treating the medium as it is built up from sequentially applied layers, building up layers of different concentrations of light-sensitive matrial, and developing diffusion regions at interfaces of layers within the holographic recording medium.

Abstract: A method for treating photosensitive, hydrophilic gelatin holograms to reduce swelling when the gelatin is exposed to moisture. Two reactants which are capable of forming solid reaction products are migrated into the interstitial voids within the gelatin to form a filled gelatin which is resistant to both swelling and shrinkage due to moisture variations. Embodiments are disclosed in which the reactants are migrated simultaneously and sequentially into the gelatin. Examples of a first reactant are silane, chloronated silanes (trichlorosilane and tetrachlorosilane, fluorosilane) and a second reactant oxygen, ammonia, water vapor and suitable gaseous sources of oxygen.

Abstract: Light sensitive recording medium is exposed to highly absorbed incoherent light either before or after a slant fringe hologram is recorded therein to reduce the sensitivity of the medium at surface regions adjacent a supporting substrate. The fringes recorded in the area of reduced sensitivity have lower contrast than those recorded in the remainder of the medium, freeing the fringes from the substrate and allowing greater expansion of the medium during a subsequent chemical swelling process. The increased swelling amplifies the refractive index modulation in the medium to increase the diffraction efficiency of the hologram. Dye may be added to the medium to increase absorbance of the incoherent light.

Abstract: The holograph assembly has first and second hydrophobic substrates layers (14, 12) which carry therebetween a water absorbent layer (16). The holographic image layer (18) is protected against moisture from that side because the water absorbent layer acts as a sponge for the moisture diffusing through the first substrate (14). The upper side of the image layer is protected by first and second cover layers (20, 22) and second water absorbent cover layer (24), all of which must be transparent to view the holographic image. An adhesive may be applied between layers.

Abstract: A holographic recording medium is treated to eliminate side lobes. The method involves exposing opposed surfaces of the medium with filtered incoherent light either before or after a holographic exposure with coherent light. The incoherent exposure produces controlled desensitization of the medium, resulting in a sensitivity profile which increases continuously to a maximum near the center of the layer. A hologram recorded in the layer has a refractive index modulation which is high in the center of the layer and which decreases toward the surfaces of the layer.

Abstract: A method of producing coherent radiation signals which have reduced coherent noise content. The method involves modulation of the position of an apodizer or aperture disposed in the optical path of the radiation provided by the coherent radiation source. The modulation causes diffraction patterns created by the apodizer or aperture to be unstable, hence reducing the noise content of the transmitted radiation. In particular, a method of producing holographic exposures containing reduced coherent noise content is disclosed. The positions of apertures or apodizers utilized in producing the holographic exposure are modulated during the exposure process. The modulation is on the order of wavelengths of the illuminating radiation used to produce the exposure. The position modulation creates a slight fogging of the exposure due to the noise, but the desired hologram is recorded with little or no decrease in efficiency.

Abstract: The systems of the invention form improved reflection and transmission holograms utilizing two beams and eliminating all of the higher energy spurious holographic recordings that are caused by reflections of rays from the outer surfaces of the cover plates. The systems provide movement of the cover plate or movement of the substrate and recording medium during the recording period to prevent formation of the spurious recordings. In some arrangements of the invention, global phase shifters are utilized to maintain the phase of the primary rays forming the desired hologram at a high level.

Abstract: A hologram forming system for forming, from a single beam source and a reflective mirror, a reflective hologram in which spurious reflection and transmission hologram recordings are eliminated. Reflected rays are changed in phase relative to the primary beams during the recording period so that spurious holograms do not form. The remaining effect of the reflected rays is to slightly change the overall refractive index of a phase recording material (such as dichromated gelatin) with a resultant slight loss of available index of modulation or to slightly, uniformly, darken an amplitude hologram film, (such as silver halide) with a slight loss of available contrast. The invention includes hologram forming systems that move the cover plate relative to a fixed recording medium with and without a phase shifter in the primary beam and a hologram forming system that moves the substrate and mirror relative to the fixed cover plate.

Abstract: The hologram forming systems of the invention form diffusion type holograms in which undesired spurious transmission hologram recordings are eliminated. The reflecting surfaces are moved during the recording process so that the reflected rays change in phase relative to the primary recording beams and spurious holograms cannot be recorded with sufficient intensity to form undesired reflections in the developed hologram. Thus, pictorial type holograms such as jewelry holograms or art holograms do not present undesired ghost images or flare patterns to the viewer. The concepts of the invention also include formation of diffusion type holograms for high gain directional viewing screens.

Abstract: An improved process is provided for attaching layers of hydrophilic, photosensitive materials onto hydrophobic plastic substrates, which comprises forming a layer of a polycrystalline, optically transparent, moisture barrier material on the substrate, followed by depositing thereon a layer of a hydrophilic, polar material, prior to depositing the photosensitive layer thereon. The process is especially suitable for the fabrication of pre-holographic elements and holograms. Holograms are fabricated by exposing and developing latent images in the photosensitive layer of pre-holographic elements and attaching to the photosensitive layer by an optical adhesive a protective cover layer comprising a plastic substrate coated with the moisture barrier material and the hydrophilic material. Additional moisture barrier protection may optionally be provided by forming a combination of moisture barrier layers and hydrophilic layers on the outer surfaces of the plastic substrates.

Abstract: An improved method for fabricating a light weight dichromated gelatin hologram package on plastic or glass substrates is provided. The prior art cover plate protecting the gelatin layer is eliminated by depositing on the gelatin a material providing a barrier to atmospheric moisture and possessing abrasion-resistant properties. In one embodiment, the photosensitive gelatin layer is deposited on a plastic substrate employing at least one subbing layer which provides a barrier to atmospheric moisture. Protection of the gelatin layer is provided by a plasma deposited silicon nitride film thereon.

Abstract: Erasable thermoplastic image recording systems having extended useful lifetimes are provided by subjecting the thermoplastic recording medium to a sequence of erasure, exposure to incident radiation cooling and projection in an inert atmosphere while applying corona charge throughout the erasure and exposure cycles. By exposing at a time when the medium is cooling from the erasure step, a heat development step is eliminated which eliminates nearly 50% of the thermal degradation of the thermoplastic polymer. Exclusion of oxygen from the system eliminates the considerable chemical degradation the film suffers from reaction with ozone. Erasure in the presence of a uniform corona charge provides more complete erasure than standard procedures. Lower temperature and shorter heating pulses are permitted with a lower surface tension thermoplastic polymer provided by external plastization of the thermoplastic. The lower surface tension also results in less noisy images and greater lifetimes.