An experimental frequency reference locks a laser to an iron absorption line in sunlight. The preprint reports measurements of solar oscillations and a partial eclipse, linking the signal to an atomic time standard. Long averaging improved precision, with detrending needed for the strongest result. Proposed measurements of other stars remain beyond what the experiment demonstrated.
Researchers made a laser track the centre of an iron absorption feature in sunlight. Their arXiv preprint presents an experimental optical frequency reference, rather than a new planet detection. An optical frequency comb, which connects optical frequencies to a time standard, tied the measurement to the SI second. The solar line lies at 1565.28 nm. Its changing frequency carries information about motion across the visible solar surface.[1]
The reported uncertainty in velocity was about 4.7 m/s when measuring for 1 second. Several thousand seconds of averaging, combined with removal of a linear trend, brought precision to approximately 30 cm/s. Telescope pointing and natural solar variability affect the longer record. The two performance figures therefore describe different integration times and processing conditions. The authors resolved oscillations of the Sun with a period near 5.5 minutes.[1]
During the partial eclipse of April 2024 in Boulder, the apparatus followed the velocity change measured as different rotating portions of the solar disc were obscured. This added an astronomical test to maintaining the laser lock. Calculations considered applying the approach to other stars using larger telescopes. Those applications remain projections. Stellar surface structure and oscillations introduce variability, so collecting more light does not automatically remove every limitation in a planet search.[1]
