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Basics Laser Spectroscopy




LAS - Laser Absorption Spectroscopy


TDLAS - Tuneable Diode Laser Spectroscopy



describes a method in which conclusions regarding the concentration or density of gas or gas components, that have to be examined, can be made from the measured absorption. Due to the laser diode(s) as the radiation source, the LAS or TDLAS is counted to the method of laser spectroscopy. TDLAS has established itself as the term for the use of laser diodes in the NIR range, whereas the term LAS includes general laser technologies in the MIR range like the distributed feedback (DFB) laser, the quantum cascade lasers (QCL), the External Cavity EC-QCL or the Intercavity Laser (ICL). 


The absorption takes place in different spectral regions and is caused by transitions between different energy states of an atom or molecule.  When working with infrared radiation, usually different vibration-rotational oscillations of a molecule occur, which are responsible for the absorption of light.


The emission wavelength of the light source - usually a laser - must be variable in this process. This is in tunable laser diodes, for example VCELS, QCL (Quantum Cascadum laser), DFB (Distributed Feedback) possible by changing the current through the laser diode or by changing their temperature. This makes it possible to take an absorption spectrum of the tuning range, which can be evaluated then.


In addition to the density, it´s possible to draw conclusions concerning the pressure and temperature of the gas on the basis of the absorbance with the TDLAS.


The TDLAS finds nowadays application in the study of particle densities in plasmas, in environmental engineering (determination of concentrations of pollutants), in determining the composition of the atmosphere as well as in medical technology.

KNESTEL offers customers an OEM LAS module consisting of Herriott long path cell, laser driver, evaluation module and control unit with software as well as the integration into a complete OEM analyzer in various sizes. Contact us.



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