Complex spectral line profiles resulting from cryogenic deformation of the SINFONI/SPIFFI diffraction gratings

Elizabeth M. George; Dominik Gräff; Michael Hartl; Heinrich Huber; Frank Eisenhauer; Helmut Feuchtgruber

doi:10.1117/1.JATIS.3.3.035002

27 July 2017 Complex spectral line profiles resulting from cryogenic deformation of the SINFONI/SPIFFI diffraction gratings

Elizabeth M. George, Dominik Gräff, Michael Hartl, Heinrich Huber, Frank Eisenhauer, Helmut Feuchtgruber

Author Affiliations +

Journal of Astronomical Telescopes, Instruments, and Systems, Vol. 3, Issue 3, 035002 (July 2017). https://doi.org/10.1117/1.JATIS.3.3.035002

Abstract

The integral field spectrograph, spectrometer for infrared faint field imaging (SPIFFI), has complex line profile shapes that vary with wavelength and pixel scale, the origins of which have been sought since the instrument construction. SPIFFI is currently operational as part of SINFONI at the Very Large Telescope (VLT) and will be upgraded and incorporated into the VLT instrument enhanced resolution imager and spectrograph (ERIS). We conducted an investigation of the line profiles based on the measurements we could take with the instrument calibration unit, as well as laboratory measurements of spare SPIFFI optical components. Cryogenic measurements of a spare SPIFFI diffraction grating showed significant periodic deformation. These measurements match the cryogenic deformation expected from bimetallic bending stress based on a finite element analysis of the lightweighted grating blank. The periodic deformation of the grating surface gives rise to satellite peaks in the diffraction pattern of the grating. An optical simulation including the cryogenic grating deformation reproduces the behavior of the SPIFFI line profiles with both wavelength and pixel scale as measured with the instrument calibration unit. The conclusion is that cryogenic deformation of the diffraction gratings is responsible for the nonideal line profiles, and that the diffraction gratings should be replaced during the upgrade for optimal instrument performance.

CC BY: © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Citation Download Citation

Elizabeth M. George, Dominik Gräff, Michael Hartl, Heinrich Huber, Frank Eisenhauer, and Helmut Feuchtgruber "Complex spectral line profiles resulting from cryogenic deformation of the SINFONI/SPIFFI diffraction gratings," Journal of Astronomical Telescopes, Instruments, and Systems 3(3), 035002 (27 July 2017). https://doi.org/10.1117/1.JATIS.3.3.035002

Received: 16 March 2017; Accepted: 20 June 2017; Published: 27 July 2017

ACCESS THE FULL ARTICLE

JOURNAL ARTICLE
16 PAGES

DOWNLOAD PAPER SAVE TO MY LIBRARY