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Magic mirrors: Secret pictures hidden utilizing liquid crystals

A way borrowed from historical “magic mirrors” makes use of liquid crystals to hide pictures from all however the correct of sunshine



Physics



5 May 2022

Han dynasty magic mirror

A Han dynasty magic mirror. When brilliant mild shines onto the mirror it displays a hidden sample close by

Robert Kawka / Alamy Stock Photo

Windows and mirrors embedded with liquid crystals can conceal pictures that seem solely when the correct of sunshine is shined on them. The approach, impressed by a 4000-year-old trick for constructing “magic mirrors”, could also be a step in direction of growing higher shows for 3D pictures.

A magic mirror or window appears to be like clear till a light-weight is shined onto it to disclose a secret picture. Craftspeople in historical China and Japan made magic mirrors out of bronze that equally hid pictures, however physicists solely started to grasp how they work round 15 years in the past.

Felix Hufnagel on the University of Ottawa in Canada and his colleagues used these insights to construct a brand new kind of magic mirror and window. Their variations comprise a state of matter often known as a liquid crystal. While liquids stream freely and crystal atoms are organised in stiff grids, liquid crystals break up the distinction: their molecules are each fluid and organized in patterns.

Magic mirror

A magic mirror reveals a picture

Hufnagel et al.

Many tv screens make use of liquid crystals as a result of their properties, like  color, might be managed by altering the patterns of the molecules. The new approach makes use of the same thought, making use of an electrical voltage to the liquid crystals to point out totally different pictures. “By tailoring the orientation of the molecules, we essentially decide what image will be formed,” says Hufnagel.

For millennia-old mirrors, very slight bumps and indentations on their surfaces made mild bounce off in simply the precise technique to kind a picture. By comparability, the liquid crystal magic home windows are utterly flat and clean.

The researchers had been additionally in a position to resolve precisely what properties the sunshine should have to uncover the hidden picture, equivalent to its polarisation. Using the fallacious type of mild ends in nonsense pictures or the unfavourable of the hidden picture.

Images revealed by the brand new approach look clear when considered from totally different angles and distances. The researchers say this implies it may very well be used to enhance projectors for 3D pictures, which regularly solely present a pointy picture when the viewer faces them good.

Journal reference: Optica, DOI: 10.1364/OPTICA.454293

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