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Microstructures make polymers lase

10 Sep 2002

Researchers say a simple embossing technique is an alternative method for making mirrorless polymer lasers.

Researchers from the UK universities of St Andrews and Exeter have made microstructured polymers using a simple embossing technique. The team believes this is the first time that the embossing has been used to make photonic structures in light-emitting polymers. (Applied Physics Letters 81 1955)

The approach, known as hot-embossing, also offers an efficient and simple alternative to complex fabrication schemes such as photolithography, electron-beam lithography and chemical etching.

To emboss the microstructures, the researchers press the polymer against a master pattern and heat it to 200°C. At this temperature, which is above the polymer's glass transition temperature, the polymer begins to soften and take-on the pattern of the template.

Cooling allows the polymer to drop below its transition point, leaving the pattern imprinted on the surface. "The resulting microstructures have dimensions of 400 nm," says group leader Ifor Samuel. "And we believe we can make smaller structures with this technique."

Samuel's group has already fabricated efficient LEDs and is now applying this approach to control light-emission from polymer-based lasers. "Microstructures can modify the light emission from polymer films by Bragg scattering," explains Samuel. "You can get feedback using this Bragg effect. No mirrors are involved."

The team's initial microstructured-lasers are based on a polymer emitting at 620 nm and produce pulses with powers on the order of 10 nJ. The system is optically pumped using a nitrogen-pumped dye laser, but Samuel believes there is scope to reduce the overall size of the system.

"By changing the polymers, there is the potential to get other colours," Samuel told Optics.org The devices are also tunable, thanks to the broad emission spectrum characteristic to the polymers.

According to Samuel, a tuning range on the order of 20 nm is possible. "This gives the potential to reach wavelengths where there are currently no sources available," he says. The group is now continuing its investigation into the effects of microstructures on light and hopes to make a more practical system.

This work was carried out in the Organic Semiconductor Centre as part of the Ultrafast Photonics Collaboration.

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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