Jahjah and colleagues address this important scientific and societal need using an innovative optical technique that involves a quantum cascade laser (QCL). While other studies and other instruments have made use of QCLs, this instrument is one of very few using a quartz tuning fork as the detector. The absorbing gas, methane or nitrous oxide in this case, absorbs the optical energy from the modulated laser, heating the gas and producing an acoustical wave that bends the tuning fork and creates an electrical signal due to the quartz piezoelectricity. While this detection method may not have the ultimate sensitivity of an optical sensor, it has the very large advantage of not requiring cooling of the detector, often using liquid nitrogen or multistage thermoelectric cooling.
An extremely attractive feature of this sensor is its ability to perform sensitive measurements with a very small (few mm3) gas sample, a tremendous advantage over many other existing sensors. The sensor is also suitable to be fabricated into an ultra-compact system based on surface mounted digital electronics. This kind of advance in the integration of all sensor components into a single surface mounted system is what is required to make this new generation of sensor broadly applicable to environmental measurements.
As this type of sensor package is made even more compact and more sensitive it will be very useful in the identification of the source strengths of methane, nitrous oxide, and other gases important to atmospheric chemistry and climate change.
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