'Anti-laser' built for first time

An anti-laser – which absorbs light rather than emitting it – has been built for the first time.

A laser shines by producing a cascade of photons that bounce around inside a light-amplifying material before exiting from one or both ends.

In 2010, Douglas Stone at Yale University and colleagues devised a way to reverse the process, with a material that absorbs rather than amplifies light.

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

Now, a team led by Hui Cao of Yale has done just that using a 110-micrometre-wide slab of silicon.

The researchers chose the wavelength of the laser light so that light waves hitting the outside of the slab from the laser beams were in just the right phase with the waves transmitted through the material to trap the light inside the slab.

The silicon absorbed 99.4 per cent of near-infrared light with a wavelength of 998.5 nanometres, turning it into heat. “Theory and experiment matched very well,” says Stone. “We couldn’t have expected to do any better.”

Future computers may use light to transmit signals efficiently between their chip processors. Anti-lasers could be used to modulate the intensity of that light, or to convert light signals into electrical form for on-chip processing, the researchers say.More than 50 years after the invention of the laser, scientists at Yale University have built the world’s first anti-laser, in which incoming beams of light interfere with one another in such a way as to perfectly cancel each other out. The discovery could pave the way for a number of novel technologies with applications in everything from optical computing to radiologyConventional lasers, which were first invented in 1960, use a so-called “gain medium,” usually a semiconductor like gallium arsenide, to produce a focused beam of coherent light — light waves with the same frequency and amplitude that are in step with one another.

Last summer, Yale physicist A. Douglas Stone and his team published a study explaining the theory behind an anti-laser, demonstrating that such a device could be built using silicon, the most common semiconductor material. But it wasn’t until now, after joining forces with the experimental group of his colleague Hui Cao, that the team actually built a functioning anti-laser, which they call a coherent perfect absorber (CPA).