Tunable Diode Laser Absorption Spectroscopy

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Tunable Diode Laser Absorption Spectroscopy ( TDLAS , in German for "absorption spectroscopy by means of tunable laser diodes") is a process with whichthe concentration or density of the gas or gas componentto be examined(for example methane or water vapor ) is determinedfrom a measured absorption . A laser diode is usedas the source of the radiation , which is why the TDLAS is one of the methods of laser spectroscopy .

The absorption takes place in lines that are caused by transitions between different energy states of an atom or molecule . If the wavelength of the laser radiation used is in the optical range , these are usually transitions between different electronic energy states. If infrared radiation is used, the absorption usually occurs between different vibration-rotation states of a molecule.

In the TDLAS, the radiation is generated with tunable laser diodes, the emission frequency of which can be varied by varying the current through the laser diode or by its temperature .

In addition to determining a density from the measured absorption of a line, conclusions can be drawn about the pressure and temperature of the gas from the profile of the line.

The TDLAS is used nowadays in the investigation of particle densities in plasmas , in environmental technology (determination of pollutant concentrations) and in the determination of the composition of the earth's atmosphere.

Web links

  • Johannes Kunsch: Diode laser absorption spectroscopy on the way to commercial importance (PDF, 411 kB)