Upgrade and Characterization of the SPIFFI/SINFONI optics

TL;DR

This paper details the upgrade and performance characterization of the SPIFFI/SINFONI optical system, focusing on the effects of new optical components and surface deformations on spectral resolution and image quality.

Contribution

It provides a detailed analysis of the optical performance improvements and the impact of upgraded mirrors on the spectrometer's line spread function and throughput.

Findings

Improved spectral resolution after upgrade

Changes in line profiles due to mirror surface deformation

Enhanced throughput ratio post-upgrade

Abstract

The SPIFFI integral field spectrometer is operated as a subunit of the AO instrument SINFONI on the VLT. It will be upgraded and reused as SPIFFIER in the new VLT instrument ERIS. In January 2016 an early upgrade of several optical components was carried out to make use of new technological developments before ERIS will be commissioned in 2020. This Master's thesis focuses on the determination and detailed description of the gain in performance due to the upgrade, with a particular focus on measurements of the exchanged diamond turned mirrors of SPIFFI. An analysis of the surface deformation of these mirrors is done, followed by a determination of the resulting collimator wavefront and its influence on the line spread function of the spectrometer. A careful analysis on the shapes, the variations and the changes of the spectral line profiles due to the upgrade is done. Furthermore, the spectral resolution, the image quality an the relative pre- and post- upgrade throughput ratio are evaluated. Finally these observed quantities are linked to critical optical components that limit the performance of the instrument.