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Tunable organic laser emits blue light

07 Jun 2004

Biomedical applications may benefit from an organic solid-state laser tunable between 401 and 434 nm.

Researchers in Germany claim to have developed the first organic solid-state laser to emit pulsed deep blue light. The team says the source tunes from 401.5 to 434.2 nm and opens the way for cost-effective bio-fluorescent monitoring and diagnosis. (Applied Physics Letters 84 4693)

According to Thomas Riedl from Technical University Braunschweig, one of the main challenges was finding a stable organic material that emits in the deep blue. Riedl and colleagues teamed up with Covion Organic Semiconductors and identified a spriobifluorene derivative as a candidate material. The Frankfurt based firm synthesized the compound.

The laser is based on a segmented distributed feedback (DFB) grating, with each device having up to six separated Bragg grating segments. A thin film of the organic material is deposited on top of the grating. Optically pumping a different segment of the grating adjusts the laser’s wavelength. The intricate grating design was fabricated by PTB (the German metrology institute) using e-beam lithography.

“Although the gratings we use are silicon based, they could be made from polymers once an initial reference has been formed,” Riedl told Optics.org. “This would allow a very cheap device, suitable for even single-use applications.”

The team pumps its DFB laser with a nitrogen laser emitting 337 nm 500 ps pulses at a rep rate of 20 Hz. The result is 3 W of pulsed output tunable over 32.7 nm. Riedl says that such a wide tuning range will give scientists more freedom in their choice of fluorescent bio-markers. With less emphasis on the wavelength source, the marker could be matched more effectively to its biological application.

The German group now hopes to extend the laser’s emission range into the UV to produce a source spanning from 370 to 750 nm. This requires tighter control of the lithography process. Recognizing its potential commercial value, the team is actively seeking development partners.

This work has been funded by the German Ministry of Education and Research ( BMBF) under contract FKZ 13N8166.

James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.

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