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Researchers are only just beginning to realise the potential of laser-based gas measurements to improve safety and reduce the impact of combustion energy on the environment.

Dr Sean O’Byrne and other members of the Defence and Security Applications (DSA) Research Centre at the University of New South Wales at the Australian Defence Force Academy, are using small lasers to monitor the greenhouse gases produced by automobiles and industry, providing the means to make combustion more efficient and less damaging to the environment.

“If we are to continue using combustion to meet our energy needs, we need to ensure that the combustion is as efficient and clean as possible”, says Dr O'Byrne. “Working on laser sensors will help achieve this aim by measuring the temperature of the flame and the concentration of greenhouse gases such as carbon dioxide and methane, as well as pollutants such as nitric oxide.”

The sensors he describes use a new type of diode laser, known as vertical-cavity surface-emitting lasers, or VCSELs, to detect the combustion exhaust gases. Dr O'Byrne is the only researcher in Australia using VCSELS for combustion measurements and is one of only a few worldwide.  The lasers were originally designed for high-speed telecommunications and can change their wavelength very rapidly - up to a million times per second.  At certain wavelengths, gases absorb laser light, and the transmitted light produces a signal that acts like a fingerprint for each type of molecule that makes up the gas. Several lasers can be combined to measure different gas species simultaneously and the sensors have a variety of potential industrial applications.

One obvious application of this technology is for motor vehicles. By measuring the emission products and their temperature, the fuel and air mixture can be adjusted to provide for more efficient and cleaner burning. Sensors can be placed in the exhaust pipe of a vehicle, measuring emissions as it is driven.  By connecting the sensors to a vehicle computer, the software can change the mixture of fuel and air in the vehicle's engine and notify the driver that a tune-up is needed if the emissions continue to rise over time.

The same technology can be used in power stations, monitoring fluctuations in emissions and alerting the operators of sudden changes in emission levels or of regions in the furnace where combustion is not uniform. Such fluctuations may cause safety as well as efficiency problems.

Another potential safety application of the laser technology is its use as an oxygen sensor in aircraft fuel tanks, where oxygen entering the tank can potentially combine with an electrical spark to cause an explosion. Such an explosion is thought to have caused the Boeing 747 crash in New York in 1996, killing all 230 passengers. A diode-laser sensor can continuously monitor the tank to ensure that oxygen levels never become high enough to form a combustible mixture.