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Abstract

Reflection holograms are described and are prepared from a transmission hologram. The reflection hologram is divided into a plurality of sequential parallel notional strips each of which is divided into bands, the bands and strips extending across the hologram from one side or end to the other and being parallel. Each band of a strip contains information derived from a respective notional strip into which the transmission hologram was divided during production of the reflection hologram. Thus each strip of the reflection hologram contains information derived from the whole of the transmission hologram. The reflection hologram is produced from the transmission hologram by a process in which each band of a notional strip of the reflection hologram is exposed in turn to a respective notional strip of the transmission hologram. The reflection hologram may be copied by placing it in contact with photosensitive holographic material and exposing the latter by notional strips with reference to respective notional strips in the reflection hologram. The exposure may be by way of exposing each strip in turn using a continuous laser beam or by way of exposing several strips at once using a pulsed laser beam and a holographic optical element.

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First Claim