Beaming with a double-decker microlaser.

It's easy to overhear words whispered by someone standing near the interior wall of a circular, domed chamber. The whispers echo throughout the gallery, making the words audible to any eavesdropper elsewhere along the wall.

Infrared light injected into a microscopic semiconductor disk follows a similar course, circulating along the disk's edge for long periods with little diminution in intensity. Such a device can act as a laser, spraying coherent light that fans out from the disk's rim (SN: 11/23/91, p.327).

Now, a team of researchers at Northwestern University in Evanston, Ill., and the University of California, San Diego, has found a way to channel the emitted laser light into a beam without greatly degrading the quality of the disk in which the light initially circulates.

Northwestern's Seng-Tiong Ho and his collaborators accomplish this feat by placing a second disk atop the first, joined by a narrow neck. Photons slowly leak from the bottom to the top disk. These photons then leave via a notch cut into the upper disk (see illustration).

"This seems to be an effective way to get the light out in a directed manner," Ho says. "Eventually, we want to make the light come out vertically."

Constructed from disks only 5 micrometers in diameter and mounted in air on a pedestal, this double-decker microlaser is considerably smaller than the tiny semiconductor lasers that scan discs in compact-disc players. "We can make them as small as 2 or 3 [micrometers] in diameter," Ho says.

Ho described the group's experiments at an Optical Society of America meeting, held this week in Dallas. Further details will appear in a forthcoming issue of APPLIED PHYSICS LETTERS.