Hologram
A diffractive optically variable device. Optical properties of the hologram are defined in terms of diffraction of light going through a diffraction grating. Optical effects occur when changing the angle of observation or illumination. Holograms may contain nano-, microprinting, microimages, covert laser readable images, etc.
Classification of holograms by optical properties:
- Reflection holograms form an image in reflected light. Aluminum foil or a transparent dielectric which reflects not more than 10-20% of light (transparent hologram) are used as a reflection layer.
- Transmission holograms form an image in transmitted light.
KINEGRAM® is a patented solution produced by the Swiss manufacturer OVD Kinegram and used for protection of security documents and banknotes.
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Fig. 1. Romania. Temporary passport issued in 2016:
a — page 2; b — the same. Holograms over the whole document page; c — the same. Diffractive identification device DID® (lower frame, fig. 1b); d — the same. Microtext (upper frame, fig. 1b)
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Fig. 2. Iraq. Special passport issued in 2011:
a — page 3; b, c, d — the same. Zoomed fragment. View at different angles of observation
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Fig. 3. Great Britain. Visa issued in 2004:
a — visa in the form of a sticker; b, c — the same. KINEGRAM®. View at different angles of observation; d — the same. Nanotext (zoomed fragment of the letter K)