Tunable Diode Laser Spectrometry is an infrared absorption measurement which utilizes the interaction of infrared light with gas molecules to determine the concentration of a target gas. The absorption of infrared light by the gas molecules causes a decrease in IR radiation intensity on the detector/photo diode.
A standard TDLS setup consists of a laser diode, optical lens, gas sample cell and a photo detector. The optical lens in the system collimates the laser light to ensure the light is perpendicular as it hits the photo diode. The laser diode in the detector is tuned to the characteristic absorption lines of a material in a sample gas. Therefore, one laser/detector will be used to measure one gas with little to no chance of any cross-sensitivity with other species in the sample.