Absorption based Sensors

NO Sensor

Due to environmental concerns and shrinking resources, combustion control is becoming increasingly more important. An important pollutant in combustion processes is NO. We are therefore developing a NO sensor based on modern laser technology. We also have a CO sensor in preparation.

The sensor is based on absorption in the UV spectral range. The UV range has the advantage that typical transition strengths are stronger such that the ultimate sensitivity can be higher than with comparable sensors in the infra-red range. Another advantage is that no background signal due to the absorption of other species are present.

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Photograph of the NO Sensor Setup


The UV light is generated by frequency summing a blue diode laser in an external cavity (395 nm, 9 mW) with a diode pumped, frequency doubled Nd:YAG laser (532 nm, 100 mW) in a beta barium borate crystal (BBO). In the one-pass configuration we generate approximately 300 nW of light at around 226 nm, which corresponds to the X-A transition in NO.

The measurement is performed using two photo-multiplier, one for the reference and the other for the signal itself. So far we have achieved a sensitivity of 5 ppm per m absorption length in the laboratory.

Principle setup of the NO sensor.
Sample spectrum including a fit of the theoretical model to the data.


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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