Scientists have developed a holographic laser projector that is significantly more efficient than today's models and could be incorporated into handheld devices ð allowing you, for instance, to project snaps from a phonecam onto a wall.

It could also be used to replace the screen on a notebook or PDA.

The principle of the projector has been known for some time but has never been translated into an effective product.

The Photonics and Sensors group at Cambridge University's Department of Engineering says it has made a number of breakthroughs, including a custom chip that can generate 200 holograms a second ð four times faster than that needed for 50 frames per second video.

It has also managed to produce sharp images with virtually no 'speckle', a common fault of holographic images.

A character of the diffracted image is that it remains in focus at any range and so does not need a focusing lens.

A company called Light Blue Optics has been spun off to exploit the technology; many of its staff, like director Edward Buckley, are still finishing their PhDs at the university.

The delicate, expensive and short-lived Halide lamps used in today?s projectors translate only a fraction of the energy they use into light. A laser translates much more and nearly all of it is used to create the image.

'We steer light,' said Buckley. 'Other projectors work by blocking light. They throw light away.'

The prototype, shown at a innovations forum at the St John's Innovation Centre, Cambridge, was monochrome but full-versions can be made by using red, green and blue lasers.

'Blue lasers are very expensive at the moment but prices are about to plummet with Blu-ray [the next-generation DVD technology that also uses them]. Red lasers were once as expensive but their prices plummeted when they began to be used in DVD drives.'