Comb-calibrated solar spectroscopy through a multiplexed single-mode fiber channel

TL;DR

This paper introduces a novel solar spectrograph calibration method using a laser frequency comb and a single-mode fiber channel that feeds both sunlight and comb light to achieve high-precision measurements.

Contribution

The study presents a new fiber-based calibration scheme that improves spatial mode matching and calibration accuracy for solar spectroscopy, with potential applications to faint astronomical objects.

Findings

Achieved nearly perfect spatial mode matching between sunlight and comb light.

Demonstrated the method's robustness through comparison with atmospheric absorption lines.

Showed potential for radial-velocity detection using solar oscillations.

Abstract

We investigate a new scheme for astronomical spectrograph calibration using the laser frequency comb at the Solar Vacuum Tower Telescope on Tenerife. Our concept is based upon a single-mode fiber channel, that simultaneously feeds the spectrograph with comb light and sunlight. This yields nearly perfect spatial mode matching between the two sources. In combination with the absolute calibration provided by the frequency comb, this method enables extremely robust and accurate spectroscopic measurements. The performance of this scheme is compared to a sequence of alternating comb and sunlight, and to absorption lines from Earth's atmosphere. We also show how the method can be used for radial-velocity detection by measuring the well-explored 5-minute oscillations averaged over the full solar disk. Our method is currently restricted to solar spectroscopy, but with further evolving fiber-injection techniques it could become an option even for faint astronomical targets.