ESPRESSO fiber-Link upgrade: III - alignment and integration activities

Abstract

The ESPRESSO spectrograph is a high resolution, super stable echelle cross-dispersed fibre-fed spectrograph, installed in the ESO-VLT Combined Coude Laboratory of the ESO-VLT in Cerro Paranal. In the framework of the Fiber-Link (FL) recovery project, which was necessary to meet the throughput requirement of the instrument, we redesigned and build the whole fibre bundle. The FL subsystem of ESPRESSO is composed by the Input Ends (IE), one per telescope and observing mode, which inject the telescope light into the fibres, the double scrambler and the light combiner for the multi-telescope mode, which merges the light of the four telescopes in a single fibre, and the spectrograph entrance slit. In this paper we focus on the alignment strategy, the tools developed and the activities performed to integrate the different components of the FL. We will describe the gluing system of the mini-lenses on the fibre ends, to guarantee the field and pupil centration; the integration of the IE, where the position and telecentricity of the two channels (star/sky) were necessary to meet the interface with the telescopes; and the integration of the beam combiner for the multi-telescope mode, particularly demanding for the small scale of the elements to integrate and the high accuracy required to guarantee the high throughput. We will also show the procedure for the scrambler alignment for the single telescope modes and the multi- telescope mode developed in laboratory and replicated at the telescope.