Laser technology reveals hidden gases in complex mixtures

Laser Network reported on January 11th that modern equipment has been fine tuned to detect highly specific gases, including trace gases found in the atmosphere, gases present in combustion exhaust emissions, and gases used in technology plasma applications.

They achieve this by calculating the percentage of light at a certain wavelength that is absorbed or attenuated by the sample. This way, the concentration of the gas can be calculated. The chemicals to be tested determine which detection wavelength should be used. In fact, multiple molecules can absorb the same amount of light, even at carefully selected wavelengths, which is a typical problem.

The efficiency of measurement methods is limited by this phenomenon called cross sensitivity. So far, this issue has been resolved, either by conducting additional measurements at various wavelengths, such as measuring spectra, or by using gas chromatography to separate interfering gases before measurement.

Dr. Ibrahim Sadiek, a former doctoral candidate at Gernot Friedrich and Leibniz Institute of Plasma Science and Technology, has now proven that there is a simpler solution.

Scientists have created a technology that enables them to surpass this cross sensitivity in absorption spectroscopy, even when producing single wavelength data. The scientific journal Science Report recently released a feasibility study on a novel, patent pending dual species one wavelength technology based on selective optical saturation.

This new technology utilizes the optical saturation phenomenon in molecules. Only very high light intensity - now easily generated by lasers - can lead to optical saturation. Subsequently, these molecules showed "transparency" in the absorption spectrum, indicating that the light emitted by radiation is no longer weakened.

The characteristic of the corresponding gas type is the point where the sample becomes transparent. Due to the deviation of concentration measurement caused by light saturation, it was previously believed to be harmful to absorption measurement and should be avoided at all costs.

As shown by Sadiek and Friedrich's research, using selective optical saturation can even measure the number of two molecules that completely interfere with each other at a given wavelength.

For example, a typical problem in practice is the detection of very low concentrations of chlorinated hydrocarbons in the atmosphere.

Currently, his team is conducting maritime research projects to advance the application of this technology in traditional absorption spectrometers. Then, on-site measurements will demonstrate the potential for reducing cross sensitivity to better explore the exchange process at the water air interface. If trace gases have sufficiently diverse saturation intensities, this method can theoretically be used to simultaneously detect multiple trace gases.

Source: Laser Net