TDLAS

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TDLAS, an acronym for Tunable Diode Laser Absorption Spectroscopy, is a technique for measuring the concentration of certain species such as methane, water vapor and many more, in a gaseous mixture. The advantage of TDLAS over other techniques for concentration measurement is it's ability to acheive very low detection limits (of the order of ppbv). Apart from concentration, it is also possible to determine the temperature, pressure, velocity and mass flux of the gas under observation.

At times TDLAS may refer to Tunable Diode Laser Atomic Absorption Spectroscopy which is used for plasma diagnostic. Here the TDLAS technique is used for measurement of metastable atom densities or neutral atom temperature and for identification of small amounts of impurities in plasmas. It is, also, possible to correlate the metastable atom densities with the partial pressure of a particularly gas in various gases mixture plasma. The main benefit of this method compared to optical emission methods is the exclusion of spectral lines enlargement due to optical instruments used, because, this width is much smaller than Doppler width – it is about the same order as natural width (about 1MHz).

As the name TDLAS suggests, the technique employs a tunable diode laser, viz. VCSEL, DFB, etc., whose emission wavelength is tuned over the characteristic absorption lines of a species in the gas in the path of the laser beam. This causes a reduction of the measured signal intensity, which can be detected by a photodiode, and then used to determine the gas concentration. de:TDLAS