Absorption based Sensors


TDLAS (Tunable Diode Laser Absorption Spectroscopy) is a powerful tool in many sensing applications. Tunable diode lasers are powerful, narrow linewidth light sources capable of measuring the absorption of gaseous species very accurately. Using appropriate spectroscopic models the concentration of a molecular species can be calculated from the integrated absorption when scanning the laser source across a particular transition provided that the spectral region is free of background absorption from other species.

This project started as a collaboration between Dr. Robert P. Lucht (Mechanical Engineering, Purdue University) and Dr. Jerald A. Caton (Mechanical Engineering, Texas A&M University) and my group at TU Darmstadt.


The goal is the development of real-time sensors for species in the gas phase. We are aiming at absorption based sensors in spectral regions accessible only by non-linear frequency conversion. 

As an example we discuss our Opens internal link in current windowNO sensor in somewhat more detail. This work aims at a realtime sensor for NO in the exhaust of large combustion engines and turbines as used for instance in power plants in order to implement combustion control schemes to optimize the efficiency of the engines while reducing the NO emission of the exhaust. The continuous absorption technique is appropriate for such a task as we are not seeking time resolved information on the exhaust process itself, but rather the information of the entire concentration of NO in the exhaust.

Another possible application for this sensor system is a stand-alone, real-time sensor for the enforcement of the future emission standards.


  • G. J. Ray et al., Opt. Lett., 26 (2001) 1870-1872.
  • Sherif F. Hanna et al., Appl. Phys. B 75 (2002) 113-117.
  • Th. N. Anderson et al., Appl. Opt. 44 (2005) 1491.
  • Robert P. Lucht et al., US Patent 6 982 426
  • R. Barron-Jimenez, J et al., Applied Physics B 85 (2006) 185-197.


Prof. Dr. Thomas Walther

Laser und Quantenoptik
Institut für Angewandte Physik
Fachbereich 05 - Physik
Technische Universität Darmstadt
Schlossgartenstr. 7
D-64289 Darmstadt

+49 6151 16-20831 (Sekretariat)

+49 6151 16-20834 (Fax)




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