Disclosed are a holographic writing method and apparatus capable of re-writing (updating) holographic information and quickly writing the holographic information with high efficiency. In an embodiment, a holographic writing method for writing holographic information by emitting a beam at a holographic recording medium containing a photo-responsable polymer material having photoisomerization characteristics that change a molecular structure thereof by absorbing light energy, writes the holographic information by using a writing wavelength different from a maximum absorption wavelength in a light absorption spectrum of photoisomer molecule structures of the holographic recording medium. The maximum absorption wavelength is a wavelength at which light absorption rate is maximum in the light absorption spectrum. A difference between the light absorption rates of the photoisomer molecule structures at the writing wavelength is less than a difference between the light absorption rates of the photoisomer molecule structures at the maximum absorption wavelength.

A method includes providing a radiation with a predetermined intensity profile. The method also includes providing a photo-sensitive medium layer including a mixture of a photo-sensitive material and an absorbing additive. The absorbing additive has a predetermined non-uniform distribution in at least one of a direction within a film plane or a thickness direction of the photo-sensitive medium layer. The predetermined non-uniform distribution of the absorbing additive is configured to result in a predetermined non-uniform absorption of the radiation. The method also includes exposing the photo-sensitive medium layer to the radiation to form a polymer film. The optical film includes at least one predetermined birefringence variation in at least one of a direction within a film plane or a thickness direction of the polymer film.

The invention relates to a process for producing an optical casting comprising at least one volume-holographic optical element by means of at least one casting operation, the process comprising the following steps: providing a casting mould comprising a first mould section having a flat, spherical, aspherical or free-form first surface and a second mould section having a flat, spherical, aspherical or free-form second surface, the first mould section being connectable to the second mould section to form the casting mould, providing at least one holographic optical element, positioning and aligning the at least one holographic optical element with respect to the first mould section or/and with respect to the second mould section, combining the first and second mould sections to form the casting mould, introducing casting material in one or more casting steps, the casting material having a maximum viscosity at 25° C. of 100 000 mPas, curing the casting material, removing the cured casting material comprising the at least one holographic optical element from the casting mould, the at least one holographic optical element being at least partly surrounded by the casting material.

The invention relates to novel compounds which are especially suitable for use as writing monomers in holographic media. The invention further provides a photopolymer and a holographic medium comprising the inventive compounds, and an optical display, a security document and a holographic optical element comprising an inventive holographic medium.

The Disclosure concerns a laser projection arrangement and a process for the generation of virtual images, the purpose of which is to present a solution which allows a representation of multiple virtual images in different distances or planes and different points of view and that can be manufactured economically. On the arrangement side, this purpose is solved when one of at least two picture generating units that generate virtual images that differ in their wavelength and/or their polarization is arranged and when a holographic optical element is arranged on or in the projection surface. On the process side, the purpose is solved when two virtual images with different wavelengths and/or different polarizations are generated, when a holographic optical element is provided which exhibits different optical properties for different wavelengths and/or different polarizations, and when, in the case of projection of the virtual images while making use of the holographic optical element, the virtual images are represented, due to the different optical properties, at different distances from the driver and/or in different points of view from the driver.

A system is provided. The system includes a light source configured to emit an infrared light to illuminate an eye of a user. The system includes a grating disposed facing the eye and including a birefringent material film configured with a uniform birefringence lower than or equal to 0.1. The grating is configured to diffract the infrared light reflected from the eye, and transmit a visible light from a real world environment toward the eye, with a diffraction efficiency less than a predetermined threshold. The system includes an optical sensor configured to receive the diffracted infrared light and generate an image of the eye based on the diffracted infrared light.

An optical device includes a first polarization selective reflector positioned in a first orientation so that the first polarization selective reflector: receives first light in a first direction; redirects a first portion, of the first light, having a first polarization to a second direction that is non-parallel to the first direction; and receives second light in a third direction and transmit a first portion, of the second light. A second polarization selective reflector positioned in a second orientation non-parallel to the first orientation, and adjacent to the first polarization selective reflector so that the second polarization selective reflector: receives third light in a fourth direction; redirects a first portion, of the third light, having the first polarization to a fifth direction that is non-parallel to the fourth direction; and receives fourth light in a sixth direction and transmit a first portion, of the fourth light having the second polarization.

The present invention provides a novel photopolymer formulation comprising matrix polymers, writing monomer and a photoinitiator and further comprising a compound of formula (1) ##STR00001##
where A.sup.1, A.sup.2 and A.sup.3 are each independently hydrogen, fluorine, chlorine, bromine or iodine, R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are each independently hydrogen, halogen, cyano, nitro, amino, alkylimino, azide, isonitrile, enamino, formyl, acyl, carboxyl, carboxylate, carboxamide, orthoester, sulphonate, phosphate, organosulphonyl, organosulphoxidyl, optionally fluorinated alkoxy or an optionally substituted aromatic, heteroaromatic, aliphatic, araliphatic, olefinic or acetylenic radical while suitable radicals may be connected together via bridge of any desired substitution, or in that two or more compounds of formula (I) may be connected together via at least one of the radicals R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5, in which case these radicals therein constitute a 2- to 4-tuply functional bridge, with the proviso that at least one of the radicals R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 is not hydrogen. Further subjects of the invention are a photopolymer comprising matrix polymers, a writing monomer and photoinitiator, a holographic medium comprising a photopolymer formulation of the present invention or being obtainable by use thereof, the use of a holographic medium of the present invention and also a process for producing a holographic medium by using a photopolymer formulation of the present invention.

An optical device includes a first polarization selective reflector; a second polarization selective reflector positioned relative to the first polarization selective reflector so that the first polarization selective reflector directs first light having a first nonplanar polarization toward the second polarization selective reflector and the second polarization selective reflector directs at least a portion of the first light toward the first polarization selective reflector as second light. The optical device includes a first reflector positioned relative to the first polarization selective reflector so that the first polarization selective reflector directs at least a portion of the second light having a second nonplanar polarization toward the first reflector as third light.

The invention relates to a multilayer body with a volume hologram layer and a partial opaque layer, arranged on a surface of the volume hologram layer, which is present in a first area and is not present in a second area. The invention furthermore relates to a method for the production of such a multilayer body, as well as a security element and security document with such a multilayer body.