A hologram is a three dimensional image recorded onto a holographic medium. Holograms are created by forming holographic structures on the holographic medium. Incident light striking the hologram interacts with the holographic structures and undergoes diffraction. To a viewer, the diffracted light is perceived as a three-dimensional image.
Holograms have a number of uses, including for example, as artwork, in security and anti-counterfeiting devices, as a data storage medium, and to enhance solar power production. Certain applications, such as data storage and solar power production, require a high quality hologram, where the image recorded in the holograph is a very accurate representation of the actual or intended image.
Holograms are often produced by processing the holographic medium in a continuous roll-to-roll process. By “roll-to-roll” it is meant that the holographic media from a roll of unexposed film is fed through an imaging chamber and wound onto a second roll after exposure. Any stray light caused by unwanted reflection during exposure has the potential to create undesired holographic structures in the holographic medium, thereby reducing the quality of the holographic image. Non-optimal holographic elements result in holograms that differ from the original or intended image, thereby impacting the holograms performance in certain applications.
Accordingly, it would be an advance in the state of the art to provide a system and method capable of absorbing stray light generated during exposure of the holographic medium during roll to roll holographic processing so as to increase the quality of the resulting hologram.
In one implementation, a novel light absorbing holographic film for holographic processing is present. The holographic film includes a light absorbing film having a holographic medium disposed thereon. The light absorbing film comprises a substrate and a light absorption layer disposed on a first surface of the substrate. In certain embodiments a second light absorption layer is disposed on a second, opposing surface of the substrate. In other embodiments, a second absorption layer is disposed on top of the first absorption layer.
In another implementation, a system for processing holographic film is presented. The system includes a first source roll of flexible unexposed holographic film having a holographic medium and a second source roll of flexible light absorbing film that comprises a substrate and a light absorption layer disposed on a first surface of the substrate. The system further comprises an imaging chamber and a feed mechanism configured to bring a portion of the flexible light absorbing film into contact with a portion of the flexible unexposed holographic film within the imaging chamber prior to exposing the portion of the flexible unexposed holographic film to light.
In yet another embodiment, a method for processing holographic film is presented. The method including providing a light absorbing film having a substrate with a first surface and a first absorption layer disposed on the first surface of the substrate. The method further includes disposing the light absorbing film on a holographic medium and exposing the holographic medium to light.
In yet another embodiment, a light absorbing film for holographic processing is presented. The light absorbing film comprises a substrate having a first surface; and a first light absorption layer disposed on the first surface of the substrate, where the light absorption layer is a colloidal mixture of gelatin and an absorption medium.
The invention will be better understood from a reading of the following detailed description taken in conjunction with the drawings in which like reference designators are used to designate like elements, and in which:
An holographic planar concentrator (HPC) 100, shown schematically in a cross-sectional view in
As shown in
The increase in PV-conversion efficiency, in comparison with a use of a conventional PV-cell, is also achieved by using multiple junction cells that create electron-hole pairs at the expense of energy of incident light over a wider spectral range than a single junction cell. The use of holographic grating with such spectrum-splitting devices (SSD) also offers some advantages. The hologram can be designed to diffract light within a specific spectral band in a desired direction (for example, towards one PV-cell) and be multiplexed with another hologram that diffracts light of different wavelength in another direction (for example, towards another PV-cell). A precise hologram (i.e., with few or no undesired holographic structures) is necessary to optimize the amount of light diffracted within the specific spectral band.
One example of a holographic SSD 200, shown in
Referring to
Referring to
Referring to
In certain embodiments the absorption medium comprises a dye capable of absorbing a target wavelength or range of wavelengths. Further, in certain embodiments the absorption medium may comprise other materials that are (i) capable of being dissolved or suspended in the gelatin layer, (ii) that exhibit absorption characteristics at a useable thickness, and (iii) that are non-reflective. In such embodiments, the absorption medium may comprise a dichromate compound, such as and without limitation potassium dichromate or ammonium dichromate. In certain other embodiments the absorption medium comprises a silver halide. In yet other embodiments the absorption medium comprises carbon black, an amorphous carbon that has a high surface area/volume ratio.
The fluid resulting from the mixture of the absorption medium with colloidal gelatin is applied to a substrate, such as substrate 404 (
The final thickness of the colloidal gelatin layer is determined by the Beer-Lambert Law (I) and is a function of the absorption constant of the colloidal gelatin, determined in part by the choice of dye/absorption material, and the desired absorbance.
% transmittance=100*e(−t*a) (1)
where, t is the thickness of the gelatin layer and a is the absorption constant of the gelatin layer. The absorption constant is, in turn, a function of the choice of dye/absorption material used. While the thickness of the final colloidal gelatin layer applied can be calculated from the exact absorbance needed, in certain embodiments it is preferred to calculate the final thickness from a greater than necessary absorbance. As will be appreciated, increasing the thickness of the final colloidal gelatin layer to further decrease the percent transmission further ensures that all stray light is absorbed and does not degrade the final hologram. In certain embodiments the percent transmission used to calculate the thickness of the dried gelatin layer is ten times lower than required. In other embodiments the percent transmission used to calculate the thickness of the dried gelatin layer is less than ten times lower than required. In yet other embodiments the percent transmission used to calculate the thickness of the dried gelatin layer is less than ten times lower than required. In various embodiments, the thickness of the dried gelatin layer is approximately 30 micrometers or less. In various embodiments, the thickness of the dried gelatin layer is greater than 30 micrometers.
In certain embodiments the absorption layer 402 is a colloidal gelatin layer indexed matched to the substrate 404. In other words, the index of refraction of the colloidal gelatin layer 402 matches the index of refraction of the substrate 404. As will be appreciated, where the index of refraction of the colloidal gelatin layer 402 is not matched with the substrate 404, at hologram/air boundary (or hologram/liquid boundary, depending on the exposure method), the difference in the index of refraction between the holographic medium and the air will cause some light passing through the holographic medium to reflect off the hologram/air boundary and back onto the holographic medium. Referred to as “Fresnel reflection,” this reflected light can cause aberrations in the resulting hologram, thereby degrading its quality. However, by index matching the colloidal gelatin one can reduce the Fresnel reflection significantly.
The steps indicated by blocks 702-708 of
In certain embodiments the first absorption layer 504 is configured to absorb a different wavelength of light as the second absorption layer 502, thereby allowing target wavelengths to pass unhindered. In certain such embodiments, either the first absorption layer 504 or the second absorption layer 502 is configured to absorb blue/green wavelengths. In other such embodiments either the first absorption layer 504 or the second absorption layer 502 is configured to absorb red wavelengths.
In certain embodiments the first absorption layer 504 is angle dependant. In such an embodiment, absorption layer 504 increasingly absorbs light the greater the angle is from normal and will thus absorb stray light which reflects from the air (or other medium)/absorption layer 504 interface or the absorption layer 504/substrate 404 interface due to Fresnel reflection. As will be appreciated, if not absorbed by layer 504, such light has the ability to reflect off of surfaces back onto the holographic medium, thereby causing further aberrations.
As will be appreciated, while
To create a hologram, the resulting light absorbing film is disposed on a holographic medium such that the absorption layer is in direct contact with the holographic medium, as indicated by block 710 of
In alternate embodiments, the light absorbing film 400 may be disposed in opposite of what is shown in
Once the absorbing film has been disposed on the holographic medium, the holographic medium can be exposed and a hologram generated, as indicated by block 712 of
in certain embodiments the absorbing film is mechanically disposed on the holographic medium such that the holographic film and the absorbing film are maintained as separate structures. By “mechanically disposed” it is meant that the absorption layer of the absorption film is mechanically brought in contact with the holographic film prior to exposure as opposed to the holographic medium and absorbing medium being applied to the same substrate. In such embodiments, to generate the final hologram via continuous processing an alternative system such as system 650 of
The exposed holographic film 604 or 640 conveyed out of the imaging chamber is wound on a roll. Where a separate absorbing film is used, such as depicted in
Where the absorption medium is disposed on the holographic medium, the absorption layer is removed after the holographic medium has been exposed, as indicated by block 714 of
While the invention is described through the above-described exemplary embodiments, it will be understood by those of ordinary skill in the art that modifications to, and variations of the illustrated embodiments may be made without departing from the inventive concepts disclosed herein.
For example, although some aspects of making and using Applicants' light absorbing film has been described, those skilled in the art should readily appreciate that functions, operations, decisions, etc., of all or a portion of each step, or a combination of steps, of the series of steps described may be combined, separated into separate operations or performed in other orders. Moreover, while the embodiments are described in connection with various illustrative structures, one skilled in the art will recognize that the light absorbing film can be embodied using a variety of structures. Furthermore, disclosed aspects, or portions of these aspects, may be combined in ways not listed above.
Furthermore, reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
Additionally, the schematic flow charts included are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of one embodiment of the presented method. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated method. Further, the format and symbols employed are provided to explain the logical steps of the method and are understood not to limit the scope of the method. Although various arrow types and line types may be employed in the flow chart diagrams, they are understood not to limit the scope of the corresponding method. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown.
Likewise, the described features, structures, or characteristics described herein may be combined in any suitable manner in one or more embodiments. In the above description, numerous specific details are recited to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. Accordingly, the invention should not be viewed as being limited to the disclosed embodiment(s).
This application claims priority to, and the benefit of, U.S. Provisional Patent Application Ser. No. 61/561,384, filed on Nov. 18, 2011, titled “Light Absorbing Film for Holographic Processing and Method of Using Same,” and to U.S. Provisional Application Ser. No. 61/563,371, filed on Nov. 23, 2011, titled “Light Absorbing Film for Holographic Processing and Method of Using Same,” the entire contents of both of which are incorporated herein by reference.
Number | Date | Country | |
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61561384 | Nov 2011 | US | |
61563371 | Nov 2011 | US |