![Relative stability measurement of two laser frequency combs (LFCs). Relative stability measurement of two laser frequency combs (LFCs). LFC1 (18 GHz mode spacing) is in channel A and LFC2 (25 GHz mode spacing) in channel B. a, Series of 100 spectrograph calibrations with one exposure every 61 s, 102 min in total. b, Results obtained with binned exposures of increasing size. The filled circles represent the standard deviation in A-B. The error bars quantify the uncertainty of the standard deviation estimated from the size of the statistical sample.](/sites/default/files/styles/crop_square_2_2_to_320px/public/images/news/figureStabilityLFCs_final.png?h=351fa67d&itok=znhfm24_)
Laser frequency combs (LFCs) are well on their way to becoming the next-generation calibration sources for precision astronomical spectroscopy. This development is considered key in the hunt for low-mass rocky exoplanets around solar-type stars whose discovery with the radial-velocity method requires cm/s Doppler precision. In order to prove such precise calibration with an LFC, it must be compared to another calibrator of at least the same precision. Being the best available spectrograph calibrator, this means comparing it to a second - fully independent - LFC. Here, we report on a test in
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