Frequency reference for CO2 monitoring

Key members:

A carbon dioxide (CO2) satellite mission based on the so-called LIDAR integrated path differential absorption technique (IPDA) is envisaged to improve the current understanding of the impact of this greenhouse gas on the climate system and changes. The technique consists in deducing the CO2 concentration in the atmosphere from the measurement of near-infrared laser light absorbed by this gas. The observational needs, however, impose severe requirements on the instrument, in particular on the frequency of the laser sensing CO2, as well as on its frequency stability in time.

To this aim, LTF is developing a laser system to serve as frequency reference for CO2, which operates at a 1.57 µm, a wavelength corresponding to a CO2 absorption line, and which is frequency stabilized. Rubidium (Rb) has been preferred to CO2 as absolute frequency reference because it exhibits strong and narrow sub-Doppler transition lines (~20 MHz, FWHM) at 780 nm achievable with low single-mode laser power. A centimeter-scale Rb-filled glass cell is sufficient to frequency lock a laser whereas an optical path length of several meters or more is needed for Doppler-broadened CO2 lines (~400 MHz, FWHM).The high stability reachable at 780 nm from an Rb transition is transferred to 1.57 µm using frequency conversion and modulation techniques. For compactness, the system is built around fiber-pigtailed components.
This project is being carried out in collaboration with the Deutsches Zentrum für Luft- und Raumfahrt (DLR) and Kayser-Threde GmbH and is funded by the European Space Agency (ESA).

Flyer of the final presentation

Rubidium spectrum at 780.24 nm serving as frequency reference for CO2 monitoring at 1572 nm.

Relevant publications:

  1. C. Affolderbach, G. Mileti, “A compact laser head with high-frequency stability for Rb atomic clocks and optical instrumentation”, Review of Scientific Instruments, vol. 76, 073108, 2005.
  2. F. Gruet, M. Pellaton, C. Affolderbach, T. Bandi, R. Matthey, G. Mileti, “Compact and frequency stabilized laser heads for Rubidium atomic clocks”, Proceedings of the International Conference on Space Optics (ICSO), Ajaccio, Corsica, 9 – 12 October 2012, paper 0048, 2012.
  3. R. Matthey, F. Gruet, S. Schilt, G. Mileti, “Rb-based Stabilized Laser System as Frequency Reference for CO2 Monitoring”, Proceedings of the European Frequency and Time Forum (EFTF), Neuchâtel, Suisse, 23 – 26 June 2014, to be published, 2014.
  4. A. Fix, R. Matthey, A. Amediek, G. Ehret, F. Gruet, C. Kiemle, V. Klein, G. Mileti, J. Pereira do Carmo, M. Quatrevalet,  PDF Proc. International Conference on Space Optics, Tenerife, (2014)
  5. R. Matthey, F. Gruet, S. Schilt, and G. Mileti, Compact rubidium-stabilized multi-frequency reference source in the 1.55- μ m region , Optics Lett. 40 (11), 2576-2579 (2015) PDF