The atmospheric dispersion corrector for the Large Sky Area Multi--object Fibre Spectroscopic Telescope (LAMOST)

TL;DR

This paper introduces a novel segmented lens atmospheric dispersion corrector (ADC) designed for the LAMOST telescope, which effectively corrects atmospheric dispersion while minimizing aberrations and obstruction, suitable for large FOV telescopes.

Contribution

A new segmented lens ADC design for large FOV telescopes like LAMOST that reduces aberration and fabrication difficulties.

Findings

The segmented lens ADC effectively corrects atmospheric dispersion.

The ADC design minimizes aberration and obstruction.

Applicable to other large FOV optical fiber spectroscopic telescopes.

Abstract

The Large Sky Area Multi--object Fibre Spectroscopic Telescope (LAMOST) is the largest (aperture 4 m) wide field of view (FOV) telescope and is equipped with the largest amount (4000) of optical fibres in the world. For the LAMOST North and the LAMOST South the FOV are 5 deg and 3.5 deg, the linear diameters are 1.75 m and 1.22 m, respectively. A new kind of atmospheric dispersion corrector (ADC) is put forward and designed for LAMOST. It is a segmented lens which consists of many lens--prism strips. Although it is very big, its thickness is only 12 mm. Thus the difficulty of obtaining big optical glass is avoided, and the aberration caused by the ADC is small. Moving this segmented lens along the optical axis, the different dispersions can be obtained. The effects of ADC's slits on the diffraction energy distribution and on the obstruction of light are discussed. The aberration caused by ADC is calculated and discussed. All these results are acceptable. Such an ADC could also be used for other optical fibre spectroscopic telescopes, especially those which a have very large FOV.