The detector signal is spectrally decomposed into harmonic frequency components of the laser

modulation frequency.

The second harmonic of the signal is used to measure the concentration of the absorbed gas.

Both line amplitude and line width are Both line amplitude and line width are extracted from the second

harmonic line shape.

Therefore the measured concentration is not sensitive to changes in the line shape (line amplitude and

line width).

The measured concentration is not sensitive to line shape changes (line width and line width) caused by

background gases.

Note: The analyser measures only the concentration of free molecules in a given gas and is therefore not 

sensitive to molecules bound to other molecules in complexes and molecules attached to or dissolved in

particles and droplets.

Care should be taken when comparing results with those obtained by other measurement techniques.