Laurendeau says this technique is very effective for learning about the combustion process, but he and his students had to overcome several challenges to make it work.
"The fluoresced light can be garbled by light from other sources," Laurendeau explains. "For example, the liquid fuel droplets reflect and scatter the laser light, which gives you a giant background signal that has to be separated out from the real signal you want to see. Also, there's a problem called 'quenching,' where the pollutant molecules lose their energy not by fluorescing light, but just by bumping into one another, which you also have to correct for."
Laurendeau and his students developed a method to compensate for the quenching called laser-saturated fluorescence.
"Basically, we take a measurement in two parts," he explains. "First, we shine the laser on the flame to obtain a 'signal' from the fluorescing nitric oxide. But that reading also contains a lot of background noise. We then change the wavelength of the laser so that we don't get a signal from the nitric oxide we're just measuring background. After we have all the data, we subtract the background noise out, and we're left with just nitric oxide measurements. The whole thing can be done in an afternoon."
Laurendeau also is experimenting with putting a special filter in front of the detector that could get rid of the background noise altogether.
When Laurendeau started his flame experiments in the early 1980s, little
funding was available because no one yet knew whether it would work and
there were no immediate practical ap
Contact: Amanda Siegfried