A new device that absorbs a laser beam -- an anti-laser -- could advance the development of optical computers. The anti-laser has been built by researchers at Yale University, and is outlined in the current issue of Science magazine.

Other uses could include radiology, but scientists expect more applications will emerge. After all, when a working version of the now-ubiquitous laser was first developed 50 years ago, it wasn't clear at the time what uses it might have.

'Coherent Perfect Absorber'

The anti-laser, also known as a "coherent perfect absorber," directs two lasers of approximately the same wavelength toward each other. The laser beams are separated by a cavity composed of a thin sheet of silicon.

The silicon traps the laser beams until their energy is absorbed, the beams cancel each other out, and heat is produced. The researchers said they can produce a version that generates electricity instead of heat.

The process is the reverse of a laser, where photons reverberate within a light-amplifying material until they are emitted from one or both ends. In the anti-laser, silicon creates a loss of coherence, instead of adding more photons to increase the beam's strength, much as a gain medium like gallium arsenide does in a laser.

The device was conceived last year by Yale's Douglas Stone and other researchers, and a team at the university led by Hui Cao recently built a working model. The device absorbed 99.4 percent of the near-infrared light.

'Theory and Experiment'

Stone told news media that "theory and experiment matched very well." Originally, Stone and his colleagues were working to predict what kind of materials could be used to create a laser when they developed the idea.

The new device's claim to fame is that it can absorb a specific frequency. This is the key to its possible use in optical computers. Stone said that technologies needed for optical computers are filters that can be directed at a specific light wavelength, modulators to reduce a light beam's intensity, and transducers to turn light into electricity. The anti-laser can perform all three functions inexpensively.

Next-generation computers that use optical technologies are in development by IBM, Motorola and others. In such machines, the problems of cross talk and other interference, which result from electrical signals that are close to each other in densely packed chips, do not exist.

It's not clear at the moment if anti-lasers have military uses as well. While future military applications are possible, Stone pointed out that, if a high-powered laser was pointed at the anti-laser and the anti-laser absorbed the weapon, a massive amount of heat would still result.

In 1917, Albert Einstein first proposed "stimulated emission," the process which makes lasers possible. The theory of holography, which uses lasers, was first developed in 1947, and the first optical laser was created in 1958.