Rewritable Holograms Could Open a New Chapter In Optical Security

Since their use on credit cards in the 1980s, holograms have been associated with optical security. Their distinctive rainbow colour shifting on banknotes, passports, payment cards and branded packaging, offer a quick visual confirmation that an item is genuine.

But a new piece of research suggests that the next generation of optical security could do far more: it could change and even be rewritten after it has been made.

A paper published in Light: Advanced Manufacturing ¹ describes a way of creating reconfigurable holographic patterns that simultaneously work in more than one mode. Under ordinary white light, the device shows a visible grayscale image that can be seen directly by the eye. But shine a laser on it, and it reveals a different hidden holographic image. In effect, the same structure can carry both an overt security feature and a covert one.