et al., Laser Frequency Combs for Astronomical Observations

A direct measurement of the universe’s expansion history could be made by observing in real time the evolution of the cosmological redshift of distant ob-jects. However, this would require measurements of Doppler velocity drifts of ∼1 centimeter per second per year, and astronomical spectrographs have not yet been calibrated to this tolerance. We demonstrate the first use of a laser frequency comb for wavelength calibration of an astronomical telescope. Even with a simple analysis, absolute calibration is achieved with an equiva-lent Doppler precision of ∼9meter per second at ∼1.5micrometers—beyond state-of-the-art accuracy. We show that tracking complex, time-varying sys-tematic effects in the spectrograph and detector system is a particular advan-tage of laser frequency comb calibration. This technique promises an effective means for modeling and removal of such systematic effects to the accuracy re-quired by future experiments to see direct evidence of the universe’s putative acceleration. Recent cosmological observations suggest that the universe’s expansion is accelerating