‘Anti-Laser’ Traps All Incoming Light

‘Anti-Laser’ Traps All Incoming Light

Call it the anti-laser. Instead of amplifying light, it would soak it up completely, leaving utter darkness.

A laser shines by producing a cascade of photons that bounce around inside a light-amplifying material before exiting from one end. A team at Yale University wondered what would happen if they could reverse the process, making the material absorb rather than emit a laser beam.

Most lasers emit from one end, but it’s also possible to make lasers emit two identical beams in opposite directions. This requires having identical, partly transparent layers at both ends of a slab of a light-emitting material such as gallium arsenide.

The researchers calculated that if a light-absorbing material like silicon were used instead, then at certain wavelengths, two identical laser beams shone directly at each other would completely cancel themselves out inside the material.

A paper-thin slice of silicon would normally absorb about 20 per cent of the incoming light, but the team showed that in this set-up it would cancel nearly all of the light at 945 nanometres, in the near infrared (Physical Review Letters, vol 105, p 053901).

So far the effect exists only on paper, but team member Douglas Stone says “ongoing experiments are extremely promising, and I have total confidence it can be realised.” The energy from the cancelled beams is converted into heat, but if it could somehow be turned into current, the effect could allow pulses in fibre-optic cables to be converted with high efficiency into electrical signals.

Image of laser light show by JTHammond and only used for illustrative purposes.

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