AS READERS of The Economist will no doubt recall, Tupac Shakur, a rapper, was murdered in 1996. It therefore came as a surprise, to say the least, when he appeared on stage in 2012. Clever visual manipulation it certainly was, but claims that Mr Shakur’s performance was a hologram were overblown. Holography maintains its sense of magic, but significant consumer applications have remained doggedly distant.

The growing interest in what is known as augmented reality (AR) may finally change that. AR is an approach to take the world that consumers see and overlay information or interfaces onto it. Just how that will be done is a subject of fervent speculation and sporadic, staggering investment. In October, a total of $542m was raised from investors including Google by Magic Leap, a company which deals in augmented reality technology (but no one seems to have figured out just what kind).

One of the problems, though, is that where information is to be added to the field of vision, it invariably interferes. Current AR devices like Google Glass incorporate a small screen in the furniture of the wearer’s glasses. Far from augmenting reality, such devices actually deny wearers some of it. But it may be worse than that; a paper published this week in the Journal of the American Medical Association suggests that Google Glass users actually have worse peripheral vision than those who wear glasses of a similar size. The technology creates blind spots where there were none.

Holography may provide a way out of this conundrum. Holograms are created by sending two laser beams onto a material that can capture an image, such as photographic film. One beam travels directly, and the other reflected off an object to be imaged. The criss-crossing of the two beams creates a pattern that, when itself lit up with ordinary light, projects a faithful 3D image of the object. What makes the idea suitable for AR systems is the fact that the film can be transparent.

TruLife Optics, a London-based firm, in collaboration with Britain’s National Physical Laboratory (NPL), has created a holographic element the size of a postage stamp. They start with a thin, transparent layer of a mix of chemicals familiar from traditional photographic film, including gelatin and silver halides. They create the holographic pattern by firing a laser through it onto a mirror. The incoming and reflected beams interfere in the film and leave a pattern that acts, itself, like a mirror. The firm’s idea is to use two of these transparent holograms, placed at either end of a “waveguide” that looks a bit like a microscope slide. An image projected onto one of them is turned and funnelled along the waveguide. When it hits the second hologram, it is turned again, parallel to the incoming image but shifted along a bit.

Because the whole assembly is transparent, an image projected from, say, the region of the ear in a forward direction could therefore be projected into the eye without interfering at all with vision. But the work needs more focus than that. Existing AR technologies rely on a fixed point of focus, which might lead to fatigue. Simon Hall, of the NPL, has been working with the TruLife team on a way around that. Mr Hall reckons that the solution is to use the same kit to bounce harmless infrared light off of the eye and collect what comes back. That gives clues as to where the eye is looking and, crucially, at what distance it is focused. The incoming image can then be re-focused to accommodate where, and at what depth, the wearer is looking. Or it could be used to determine that the wearer is looking away, and the image can be turned off altogether. Because, sometimes, you just want to watch Mr Shakur perform.

This article was published in The Economist on 5th November 2014.  See this link.