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ATMO-SENSE

The project ATMO-SENSE aims at taking the next steps towards the realisation of a generic gas sensing platform characterized by high sensitivity, fast response time, rugged operation and low power consumption. The photonic sensing concept to be further developed and refined is based on 2f-wavelength modulated Fabry-Pérot photothermal interferometry (PTI), which was recently developed and filed for patent at TU Wien (see Fig. 1. (right) [2]). In PTI, sensitivity and ruggedness strongly benefit from miniaturization. This is in strong contrast to classical absorption measurements, where an increase in sensitivity is typically achieved, by an increase in the optical path length, e.g. through multi-pass gas cells.
Due to its unique characteristics PTI can be applied to a wide range of different gas sensing applications, such as:
           Environmental trace gas monitoring,
           Medical applications (e.g. exhaled breath gas analysis), and

           Manufacturing / production (e.g. process monitoring and process control).

Following the research topic to be addressed by this ERA-NET project on "Photonic Sensing", we have selected an application scenario in the area of Environmental Monitoring, where measurement speed, sensitivity, ruggedness and low power consumption are crucial. We plan to measure fluxes of important trace gas molecules (N2O, CO2, O3, see Fig. 1. (left)) in the atmosphere. For flux measurements the concentration of the target trace gas molecules as well as the wind direction need to be measured. We want to develop the photonic concept which will allow performing those flux measurements in the future.

The ability to measure fluxes of trace chemical species in the atmosphere is of crucial importance in modern environmental research. Having access to time resolved concentrations of multiple chemical components up to sub-parts-per-trillion (ppt) concentration levels and applying the eddy covariance technique, reveals information on the mass transport of these chemical components. By analysing these fluxes, insight can be obtained in complex transport and exchange phenomena like e.g. geochemical compartments, atmospheric information and NxOy emission of different bacteria.


             

Fig. 1. (left) Line intensity of CO2, N2O, and O3 at 296 K with the strong absorbing background matrix of H2O [1]. (right) Fabry Pérot photothermal interferometry setup [2].

 

The main component of the PTI setup is a mid-IR interband cascade laser (ICL) [3] that is developed within the framework of this project. In order to fully exploit the low electrical dissipation capabilities of such a device, it is merged with a surface emitting 2nd order DFB grating [4], which is also beneficial for small footprint monolithic array integration.


[1] Hitran database (https://www.cfa.harvard.edu/hitran).
[2] J. P. Waclawek, V. C. Bauer, H. Moser, and B. Lendl, "2f-wavelength modulation Fabry-Pérot 
     photothermal interferometry",
Opt. Express 24(25), 28958, 2016.
[3] R. Weih, L. Nähle, S. Höfling, J. Koeth, and M. Kamp, "Single mode interband cascade lasers
     based on lateral metal gratings"
, Appl. Phys. Lett. 105, 071111, 2014.
[4] M. Holzbauer, R. Szedlak, H. Detz, R. Weih, S. Höfling, W. Schrenk, J. Koeth, and
     G. Strasser, "Substrate-emitting ring interband cascade lasers", Appl. Phys. Lett. 111,
     171101, 2017.