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Solvents make lasers in minutes

12 Jun 2003

UK researchers unveil a simple technique that can fabricate a microstructured polymer laser in a couple of minutes.

Researchers in the UK have fabricated a distributed feedback (DFB) polymer laser using a simple, soft lithography process. The team from St Andrews University claims the solvent-assisted micromolding technique, called SAMIM, can pattern a semiconducting polymer film in less that two minutes and may pave the way for development of a range of microstructured photonic devices including lasers. (Applied Physics Letters 82 4023)

Justin Lawrence and his colleagues from St Andrews’ Organic Semiconductor Centre say that because SAMIM does not involve the use of heat or pressure to pattern the polymer films, it is a fast and simple way to make photonic structures.

The first step towards making the laser is to produce a microstructured stamp, which contains the pattern and essentially acts as a template. “This stamp is then inked with a solvent and placed in contact with a light-emitting polymer film,” explains Lawrence. “The solvent dissolves the polymer, which then conforms to the microstructure on the stamp. The solvent evaporates and the stamp is removed from the polymer film.”

The result is a 120-nm-thick polymer film patterned with two perpendicular 400-nm-period gratings. The waffle-like pattern has a depth of 20 nm and is transferred from the stamp to the film in just 100 seconds.

After mounting the patterned film in a vacuum chamber, the team optically excite it using 1-ns pulses from a frequency-doubled, passively Q-switched Nd:YVO4 microchip laser. Above threshold, Lawrence says the film’s emission narrows to a linewidth of 0.6 nm at 638 nm.

According to the authors, the threshold for laser oscillation was 225 nJ and the energy of the surface emitted output was 0.1nJ for a pump energy of 450 nJ. The team is planning to reduce the lasing threshold by increasing the depth of the pattern on the film.

“One could make a single polymer lase over most of a 50-nm-range by changing the period of the microstructure,” Lawrence told Optics.org. “One could also use different polymers and do the same thing in the red, green and blue.”

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

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