DISEASE DETECTION/ENVIRONMENTAL MONITORING: Novel design makes mid-IR fiber laser super-sensitive for breath analysis

A fiber laser able to produce 25 times more light than other lasers operating at a similar wavelength has proven able to detect very low concentrations of gases.

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A fiber laser able to produce 25 times more light than other lasers operating at a similar wavelength has proven able to detect very low concentrations of gases.1 Operating in the mid-infrared (mid-IR) frequency range, the band in which many important hydrocarbon gases absorb light, it promises use in detection of diseases such as diabetes, wherein minute amounts of gases not normally exhaled can be detected in the breath. This invention of researchers at Australia's University of Adelaide is also promising for remote sensing of greenhouse gases.

"The main limitation to date with laser detection of these gases has been the lack of suitable light sources that can produce enough energy in this part of the spectrum," said project leader David Ottaway. "The few available sources are generally expensive and bulky; optical fiber makes the new laser more affordable, less bulky, and also easier to work with."

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This mid-IR fiber laser owes its ability to produce 25X the power of standard lasers to a novel setup. The result is greater sensitivity, and thus an ability to analyze breath among other gases.

Researcher Ori Henderson-Sapir explained that a novel approach helped to overcome the hurdles that have prevented fiber lasers from producing sufficient power in the mid-IR. An erbium-doped, zirconium-fluoride-based glass fiber laser operated at 3.6 μm—the deepest mid-IR emission from a fiber laser operating at room temperature—and achieved 260 mW in continuous-wave mode. Using two wavelength pump sources let the researchers leverage long-lived, excited states that would normally cause a bottleneck, and this enabled maximum incident optical-to-optical efficiency of 16% with respect to the total incident pump power. Both output power and efficiency are an order-of-magnitude improvement over similar lasers demonstrated previously. The fiber laser also exhibited the longest wavelength of operation to date for a room-temperature, nonsupercontinuum fiber laser.

The laser has the promise of efficient emission from 3.3 to 3.8 μm, meaning it has incredible potential for scanning for a range of gases with high sensitivity—making it very useful for diagnostics and sensing.

1. O. Henderson-Sapir, J. Munch, and D. Ottaway, Opt. Lett., 39, 493–496 (2014).

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