Microscopic Bundle Lases Like a Sieve

Hank Hogan

A recent innovation in lasers might make a bundle -- a microscopic bundle, anyway. Researchers at the Darmstadt University of Tech nology have fabricated a new class of microlasers by using a molecular sieve to hold an organic dye.

Constructed out of a bundle of zeolite (AlPO4-5) tubes with 0.73-nm-wide channel pores, the microlaser produces 687-nm light. The lasing action travels around the diameter of the bundle, reflecting off the internal walls of the structure. As photons make multiple trips around the bundle, the dye amplifies the beam. The result is the intense, coherent light of a laser.

A scanning electron micrograph shows a microlaser constructed with zeolite tubes. The lasing action occurs within the hexagonal boundaries of the 8-µm-diameter optical resonator (shown in outline). Courtesy of Darmstadt University of Technology.

The combination of microlasers and organic dyes is potentially useful for several reasons. Organic dyes have high output, and the wavelength produced is tunable over the entire visible spectrum. However, organic dye lasers are messy, large and power-hungry. Shrinking the optical cavity dimensions of the laser down close to the wavelength of light could potentially fix these problems. Obviously, such a microlaser would be smaller. It would also require less power because restricting the optical cavity would allow only one resonant mode.

While other organic microlasers have been built, the molecular sieve has some unique advantages. Experiments indicate that the organic dye molecules are physically and, on average, electrically aligned. That leads to a strongly polarized light beam, which could prove useful for optical sensing and communication. Also, molecular sieves have economic advantages, as pointed out by research group member Franco Laeri, a professor at the university's Institute of Applied Physics.

"Molecular sieve lasers can be mass-produced in tons with the same methods which are used to manufacture molecular sieves for the petroleum industry," he noted. "What can be achieved is a 'lasing powder.' "

The group has applied for patents, and commercialization of the technology will begin soon. Further research is needed before products can be produced, however. Some of the hurdles include electrically inducing lasing in the sieve bundles and expanding the number of organic dyes that can be used.