Design of optical frequency comb for sky survey astronomical spectrograph calibration

Sky survey telescope is an important approach to ground-based observation of external galaxies, and further research on large-scale structure of the universe, galaxy formation and evolution. Sky survey spectrograph (SSS) with low resolution is included in such kind of telescope system. The spectral measurement accuracy of SSS will determine the accuracy and scientific value of mass spectral data. Currently iodine absorption cell or Thorium-Argon lamp is adopted as the calibration source for SSS. However, the spectral lines are sparse, with non-uniform spectral interval and intensity, and even instable over long time. The novel astro-comb cannot be applied to SSS directly because the spectral intervals are still too dense to be used in SSS with relatively lower resolution. In this paper, spectral mode filtering method with acceptable energy reduction and accurate spectral line frequency is studied to improve current astro-comb to properly distributed spectral lines and solve the above critical problem. Aiming at calibration for the measuring of the spectral lines in 3700-5900 Å region, we design an improved astro-comb system based on Erbium-doped fiber laser and Fabry-Perot filter series. Feasible systematical parameters are given. It will help develop a novel calibration approach with systematic error reduction to less than 1/10000 of that of the current calibration methods.

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