CRIRES User Manual
Doc. Number: ESO-254264
Doc. Version: P109.4
Issued on:
2021-12-01
Page:
9 of 99
Document Classification: ESO Internal Use [Confidential for Non-ESO Staff]
Figure 2: Light path sketch of the upgraded CRIRES.
The CRIRES instrument mounted at UT3 of the Very Large Telescope (VLT) observatory is
an upgraded version of the original/old CRIRES (oCRIRES) instrument, which was in
operation from 2006 to 2014 at the UT1 of the VLT. oCRIRES was a unique instrument,
accessing a parameter space (wavelength range and spectral resolution) up to now largely
uncharted. It consisted of a single-order spectrograph providing long-slit (40 arcsecond)
spectroscopy with a resolving power up to R=100 000 in the wavelength regime from 0.95
to 5.2 micron. The setup, however, was limited to a narrow, single-shot, spectral range of
about 1/70 of the central wavelength, resulting in low observing efficiency for many scientific
programmes requiring a broad spectral coverage.
The CRIRES upgrade project, CRIRES
+
, has transformed this VLT instrument into a cross-
dispersed spectrograph with the goal to increase the simultaneously covered wavelength
range by up to a factor of ten. A new and larger detector focal plane array of three Hawaii
2RG detectors with 5.3μm cut-off wavelength replaced the existing detectors. For advanced
wavelength calibration, custom-made absorption gas cells and a Fabry-Perot etalon system
have been added. A spectro-polarimetric unit allows the recording of circular and linear
polarized spectra. This upgrade is supported by dedicated data reduction software allowing
the community to take full advantage of the new capabilities.
Figure 2 summarizes the overall concept of the CRIRES upgrade. The main, high resolution
spectrometer unit remains untouched. The new cross-disperser unit substitutes the old re-
imager and pre-dispersing sub-systems.
