Concave Mirror Master Hologram Verification
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Solution Overview
Problem
Existing volume reflection holograms in security documents, such as passports and identity cards, are difficult to verify as they require favorable lighting conditions, leading to incomplete information recording during reconstruction.
Innovation Solution
A method and device for producing a master hologram with a concave mirror-like property, where the reference light is designed as a diverging light field from a point-shaped or line-shaped source region, enhancing the reconstruction properties and making the hologram easier to verify by focusing the image at a viewing location.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat homogeneous diffraction structure master hologram is used, then the manufacturing process is simple and reproducible, but the reconstruction requires favorable lighting conditions and has limited angular range
Solution Approach 1:
The patent applies curvature by replacing the flat homogeneous diffraction structure with a concave mirror-like structure. This curved surface focuses incident light to a focal point, creating a conical light distribution that enhances the angular range for reconstruction and improves visibility under various lighting conditions, while still maintaining the planar holographic recording medium for simple manufacturing.
2Reliability
If a volume reflection hologram is used with high wavelength and angular selectivity, then the hologram is difficult to replicate and falsify, but the reconstruction is difficult under ordinary lighting conditions
Solution Approach 1:
The concave mirror-like structure provides the necessary angular selectivity and wavelength sensitivity for security while the focal point geometry creates a conical light distribution that is visible under ordinary lighting conditions. The curvature focuses light from various angles to the focal point, making the hologram verifiable without requiring specific lighting arrangements.
Solution Approach 2:
The patent changes the geometric parameters of the diffraction structure by introducing a curved surface with specific focal length. This modifies the light distribution pattern from a planar to a conical arrangement, enabling the hologram to be reconstructed with white light from various angles while maintaining security characteristics.
3Difficulty of detecting and measuring
If the master hologram has a concave mirror-like property with focusing capability, then the reconstruction image is focused at a viewing location improving detectability, but the manufacturing process becomes more complex
Solution Approach 1:
The concave mirror-like structure is implemented as a curved diffraction element that can be directly recorded on a planar holographic medium. The curvature is encoded in the diffraction pattern, allowing the focusing capability to be achieved without complex mechanical components, thus limiting the increase in manufacturing complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The concave mirror-like property of the master hologram improves the detectability and reconstruction of individualized volume holograms, allowing for easier verification and complete information capture, even under less favorable lighting conditions.
Implementation Method 1
The diffuse scatterer (10) is designed to transmit the incident directed first coherent light (110) and to convert it into diffusely scattered light (115)
Implementation Method 2
guided into the holographic recording material (40) as object light (119) by a Fourier lens (30)
Implementation Method 3
a second coherent light coherent with the first coherent light is irradiated into the holographic recording material (40) as reference light (129) from a side facing away from the Fourier lens in order to form a volume hologram in the holographic recording material (40)
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention relates to a method for producing a master hologram (45) for a contact copying process comprising the steps of: generating first coherent light (110) and a second coherent light (120) coherent to it; shining the first light (110) onto the diffuse diffuser (10) to generate diffusely scattered light (115), which is limited by an aperture (20) arranged immediately adjacent to the diffuse diffuser (10) and is directed by a Fourier lens (30), in one focal plane (32) of which the diffuse diffuser is arranged, into the holographic recording material (40) as object light (119); and shining the second light (120), coherent to the first coherent light (110), into the holographic recording material (40) as a reference light (129) from a side facing away from the Fourier lens (30) to align the image in the to form a planar reflection volume hologram (45) from holographic recording material (40),wherein the reference light (129) is generated as a diverging light field (128) emanating from a point-like or line-like source region (127). The invention further relates to a device for producing master holograms, a method for producing individualized holograms with a concave mirror-like hologram, and holograms of a concave mirror-like planar diffuser exhibiting a different diffraction efficiency according to an individualized pattern.