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Tiny dye laser suits lab-on-a-chip

08 Sep 2004

Japanese research could lead to miniature optical circuits that can perform spectroscopy on a glass chip.

Scientists in Japan have used a femtosecond laser to fabricate a tiny dye laser that is embedded in a block of glass (Optics Letters 29 2007). The development could be a step towards cost-effective "lab-on-a-chip" devices that use miniature optical circuits to analyse liquid samples.

"The laser could be used as an optical source for analysis like absorption or fluorescence spectroscopy," commented Koji Sugioka, a member of the team from the RIKEN research institute in Saitama, Japan that made the device. "We have already succeeded in fabricating some 3D micro-reactor structures in the same glass and we can easily integrate them and the laser in a single glass chip."

The heart of the laser is a miniature rectangular dye chamber (200 µm deep and about 600 µm wide/long) that lies 400 µm beneath the surface of the glass. This chamber is surrounded by four 45° hollow micromirrors. A central hollow bore channel is used to inject laser dye into the chamber.

The hollow structures are made by illuminating photo-etchable glass (Foturan from Schott Glass) with 145 fs pulses from a 775 nm laser operating a repetition rate of 1 kHz. The glass is then baked before the laser-exposed regions of the glass are selectively removed by etching with an acid solution. Finally, the etched sample is baked once more.

Sugioka and his colleagues Ya Cheng and Katsumi Midorikawa initially filled the finished structure with a solution containing the dye Rhodamine 6G. When they pumped it with pulses from a frequency-doubled Nd:YAG the structure started to lase at 578 nm. However, they say that the design is compatible with other laser dyes.

"We can cover every wavelength in the visible range by changing the kind of laser dye solution," said Sugioka. "We have also fabricated a micro twin dye laser that emits two different wavelengths 568 and 618 nm by a single pump laser. In this system, two hollow micro-chambers were filled with the different laser dye solutions Rh6G and Rh640."

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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