How to cloak a crime in a beam of light

The 14th member of Danny Ocean's team of thieves might just be a physicist, making use of an "event cloak" dreamed up by Martin McCall's team at Imperial College London.

Unlike invisibility cloaks, which bend light around an object, an event cloak would open up a time gap in the light by controlling its speed through optical fibres, and then seal it again to hide all traces of activity within the gap. A modified version could, in principle, allow a safe-cracker to work while the security camera appears to record an empty room.

McCall's colleague Alberto Favaro compares the way it works to the way a road packed with speeding cars can still allow a pedestrian to cross. Some cars slow down, creating a jaywalker-friendly, vehicle-free gap, before speeding up again to re-establish the seamless flow of traffic.

In the Imperial team's blueprint for their cloak, an optical fibre serves as the road, while the photons passing down the fibre take the place of the cars.

This approach relies on an unusual property of silica optical fibres: their refractive index, the measure of how fast light travels through the silica, changes with the brightness of the light. To open an event cloak in the stream of light passing down the fibre, a control laser injects an additional pulse of light. The increased brightness slows the light down, says team member Paul Kinsler.

via How to cloak a crime in a beam of light - physics-math - 16 November 2010 - New Scientist.