A Laser Frequency Comb System for Absolute Calibration of the VTT Echelle Spectrograph

TL;DR

This paper presents a laser frequency comb system designed for precise, absolute wavelength calibration of the VTT echelle spectrograph, enhancing solar spectroscopy accuracy at the meters per second level.

Contribution

The paper introduces a novel laser frequency comb calibration system integrated with the VTT spectrograph for absolute solar spectral measurements.

Findings

Successful installation of the LFC system at VTT in 2011

Achieved absolute calibration accuracy at the meters per second level

Demonstrated advantages over traditional calibration methods

Abstract

A wavelength calibration system based on a laser frequency comb (LFC) was developed in a co-operation between the Kiepenheuer-Institut f\"ur Sonnenphysik, Freiburg, Germany and the Max-Planck-Institut f\"ur Quantenoptik, Garching, Germany for permanent installation at the German Vacuum Tower Telescope (VTT) on Tenerife, Canary Islands. The system was installed successfully in October 2011. By simultaneously recording the spectra from the Sun and the LFC, for each exposure a calibration curve can be derived from the known frequencies of the comb modes that is suitable for absolute calibration at the meters per second level. We briefly summarize some topics in solar physics that benefit from absolute spectroscopy and point out the advantages of LFC compared to traditional calibration techniques. We also sketch the basic setup of the VTT calibration system and its integration with the existing echelle spectrograph.