KMOS pick-off arm optical alignment, calibration, and testing

摘要

The pick-off arm is the part of the KMOS instrument which re-images a sub-field of the VLT focal plane to a position outside of the main field where it can be used for integral field spectroscopy. In this paper we describe the optical alignment and test procedure developed to meet the challenging alignment requirements of the instrument. It is important to note that although the alignment is done at ambient temperature, the alignment of the optical components must be maintained at the instruments cryogenic operational temperature. This paper describes the methods used to achieve the absolute positioning accuracy and the test results obtained and discussed some of the practical difficulties that were encountered.