Press 'n' Peel Lasers: Coaxing light beams out of cheap plastic

Peter Weiss

Like poker chips, lasers may someday be molded out of plastic by the millions. A new laser-making method takes a major step in that direction, its Austrian developers say.

Lasers are devices that emit a coherent beam of light of a single wavelength. Their prices have been coming down over the years, but dirt cheap plastic ones could serve as the heart of mass-produced biomedical and environmental sensors and optical-telecommunications networks, the researchers say. What's more, unlike the lasers currently available, plastic ones could be flexible.

Manufacturers today rely on costly fabrication techniques for making the microchip lasers used widely in CD and DVD players and other gadgets. Those techniques require exacting procedures carried out in tightly controlled conditions and meticulously clean environments.

In the July 17 Advanced Materials, Martin Gaal and Emil J.W. List of the Graz University of Technology and their colleagues describe a simpler method of making lasers by imprinting patterns into plastic under ordinary conditions. The Graz scientists had teamed up with researchers from AT&S, a circuit board maker in Leoben, Austria.

The key to the new technique is a hard mold with a shallow grating on its surface. The nanometer-scale depths and spacing of the ultrafine, parallel ridges provide a fine structure that stimulates laser action.

To make each laser, the researchers press their mold into a droplet of solution. It contains a semiconducting polymer, known by the acronym MEH-PPV, that has been dissolved in a fast-evaporating solvent. When the coating dries, the polymer retains a negative replica of the mold's ridges. That structure, which the researchers peel from the mold, acts as a laser.

"You can imagine the grating as if it was a fingerprint," says List, who led the team. "The real step forward is the ease of fabrication," he notes. "You have nanostructures that you just press into the material. You can do it once, twice, many times. That makes the entire process very cheap."

The tough part is producing a mold with precise nanoscale ridges only 30 nanometers high and roughly 400 nm apart. To do this, the scientists rely on the same photolithographic techniques used to make microchips.

A drawback of the new approach is that the resulting lasers produce light only when stimulated by another laser. Most lasers now in use produce light directly from an electric current. List says that researchers in his lab and many others are already racing to invent electrically driven lasers made out of polymers such as MEH-PPV.

The fabrication method of the Austrian team is not entirely new, notes John A. Rogers of the University of Illinois at Urbana–Champaign. He and his colleagues have used the same approach to create relatively coarse-structured, nonlaser light sources in various shapes, such as rings. Yet List and his coworkers have attained much finer structural features and created patterns that can support laser action, Rogers says. "Those are both … impressive demonstrations," he adds.

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References:

Gaal, M. … and E.J.W. List. 2003. Imprinted conjugated polymer laser. Advanced Materials 15(July):1165–1167. Abstract available at http://dx.doi.org/10.1002/adma.200305047.

Rogers, J.A., Z. Bao, and L. Dhar. 1998. Fabrication of patterned electroluminescent polymers that emit in geometries with feature sizes into the submicron range. Applied Physics Letters 73(July 20):294–296. Abstract available at http://dx.doi.org/10.1063/1.121799.

Schueller, O.J.A. … J.A. Rogers, et al. 1999. Fabrication of photonic crystal lasers by nanomolding of solgel glasses. Applied Optics-LP 38(September): 5799–5802. Abstract available at http://www.opticsinfobase.org/abstract.cfm?id=60771.

Further Readings:

Gorman, J. 2003. Plastic electric. Science News 163(May 17):312–313. Available to subscribers at http://www.sciencenews.org/articles/20030517/bob9.asp.

______. 2000. Nobel prize recognizes future for plastics. Science News 158(Oct. 14):247. References and sources available at http://www.sciencenews.org/articles/20001014/fob8ref.asp.

Weiss, P. 2002. Making a little impression: New chip-making method may mold the industry. Science News 161(June 22):390. Available at http://www.sciencenews.org/articles/20020622/fob8.asp.

______. 1999. Plastic reaches to meet silicon guide. Science News 156(Sept. 18):189. References and sources available at http://www.sciencenews.org/pages/sn_arc99/9_18_99/note7ref.htm.

Wu, C. 1996. Plastic glows with bright laser light. Science News 150(Aug. 24):119. Available at http://www.sciencenews.org/pages/sn_arch/8_24_96/fob2.htm.

Sources:

Martin Gaal
Laboratory for Advanced Functional Materials
Institute of Solid State Physics
Graz University of Technology
Petersgasse 16
A-8010 Graz
Austria

Emil J.W. List
Laboratory for Advanced Functional Materials
Institute of Solid State Physics
Graz University of Technology
Petersgasse 16
A-8010 Graz
Austria

John Rogers
Department of Materials Science and Engineering
1304 West Green Street
University of Illinois, Urbana-Champaign
Urbana, IL 61801

From Science News, Volume 164, No. 4, July 26, 2003, p. 53.