A laser locked Fabry-Perot etalon with 3 cm/s stability for spectrograph calibration

Yulia V. Gurevich*, Julian Stuermer, Christian Schwab, Thorsten Fuehrer, Steve K. Lamoreaux, Andreas Quirrenbach, Thomas Walther

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference proceeding contributionpeer-review


Accurate wavelength calibration is crucial for attaining superior Doppler precision with high resolution spectrographs. Upcoming facilities aim for 10 cm/s or better radial velocity precision to access the discovery space for Earth-like exoplanets. To achieve such precision over timescales of years, currently used wavelength calibrators such as thorium-argon lamps(1) and iodine cells(2) will need to be replaced by more precise and stable sources. The ideal wavelength calibrator would produce an array of lines that are uniformly spaced, narrower than the spectrograph resolution, of equal brightness, cover the entire wavelength range of the spectrograph, and whose frequencies do not change with time. Laser frequency combs are an extremely accurate and stable, albeit technically challenging and costly, option that has received much attention recently.(3) We present an alternative method that uses a Fabry-Perot (FP) etalon illuminated by a white light source to produce a comb-like spectrum over a wide wavelength range. Previous work focused on the development of passively stabilized FP etalons for wavelength calibration.(4-6) We improve on this method by locking the etalon to an atomic transition, the frequency of which is known to <2 x 10(-11).(7) We use a diode laser to observe both the rubidium (Rb) D-2 transition at 780 nm and the etalon transmission spectrum. Saturated absorption spectroscopy is used to resolve the Rb hyperfine lines and precisely determine their locations. Since the etalon spectrum is probed with the same laser, the etalon can be locked by ensuring that one of its transmission peaks coincides with a particular Rb hyperfine peak (via either temperature tuning or a piezoelectric transducer incorporated into the etalon). By measuring the frequency of one etalon peak directly via comparison with the Rb, we remove any drifts or aging effects of the etalon that could cause problems for passively stabilized etalon references. We demonstrate a locking precision that is equivalent to a Doppler precision of 3 cm/s RMS.(8)

Our setup is simple and robust, can be used with various etalons, and works in the infrared as well as the visible part of the spectrum. The combination of low cost, ease of use, and high precision make this calibration system an attractive option for new spectrographs and as a retrofit for existing facilities.

Original languageEnglish
Title of host publicationGround-based and airborne instrumentation for astronomy V
Subtitle of host publication22-26 June 2014, Montréal, Canada
EditorsSuzanne K Ramsay, Ian S McLean, Hideki Takami
Place of PublicationWashington, DC
Number of pages17
ISBN (Print)9780819496157
Publication statusPublished - 2014
Externally publishedYes
Event5th Conference on Ground-Based and Airborne Instrumentation for Astronomy - Montreal, Canada
Duration: 22 Jun 201426 Jun 2014

Publication series

NameProceedings of SPIE
ISSN (Print)0277-786X


Conference5th Conference on Ground-Based and Airborne Instrumentation for Astronomy


  • wavelength calibration
  • exoplanets
  • stabilized etalon
  • radial velocity
  • Doppler technique
  • Echelle spectrograph
  • high-resolution spectroscopy
  • Fabry-Perot

Cite this