Laser to detect low levels of gases

Researchers at the University of Adelaide have developed a laser with 25 times more light emission than other lasers operating at a similar wavelength. Their research has been published in the journal Optics Letters.

The scientists will use the laser for the detection of very low concentrations of gases. Research has shown that, with various diseases, minute amounts of gases not normally exhaled can be detected in the breath; for example, acetone can be detected in the breath when someone has diabetes.

Project leader Dr David Ottaway said there have been limitations to the use of lasers for gas detection; namely “the lack of suitable light sources that can produce enough energy in this part of the spectrum. The few available sources are generally expensive and bulky and, therefore, not suitable for widespread use”.

The new laser uses an optical fibre which is easier to work with, less bulky, more portable and more cost-effective to produce than other types of laser. The researches claim their invention is “the first … erbium-doped, zirconium-fluoride-based glass fibre laser operating well beyond 3 μm with significant power”, achieving 260 mW in CW at room temperature.

“The use of two different wavelength pump sources allows us to take advantage of the long-lived excited states that would normally cause a bottleneck, and this enables maximum incident optical-to-optical efficiency,” they explained.

PhD researcher Ori Henderson-Sapir said the team was thus “able to overcome the significant technical hurdles that have prevented fibre lasers from producing sufficient power in the mid-infrared” - the frequency range where many important hydrocarbon gases absorb light.

The researchers reported light emission at 3.6 µ - said to be “the longest wavelength of operation obtained to date for a room-temperature, non-supercontinuum fibre laser”. They have also shown that the laser has the promise of efficient emission across a large wavelength spectrum from 3.3-3.8 µ.

“Probing this region of the electromagnetic spectrum, with the high power we’ve achieved, means … [the laser] has incredible potential for scanning for a range of gases with a high level of sensitivity, with great promise as a very useful diagnostic and sensing tool,” said Dr Ottaway.

Potential applications also include detection in the atmosphere of the greenhouse gases methane and ethane.

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