Doc:
Issue
Date
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VLT-MAN-ESO-14650-4942
P96
24.06.2015
21 of 161
ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
2.2.1.3 The IFU
The Integral Field Unit is an image slicer that re-images an input field of 4”x1.8” into a
pseudo slit of 12”x0.6”. The light from the central slice is directly transmitted to the
spectrographs. The two lateral sliced fields are reflected toward the two pairs of spherical
mirrors and re-aligned at both ends of the central slice in order to form the exit slit as
illustrated in Figure 4. Due to these four reflections the throughput of the two lateral fields is
reduced with respect to the directly transmitted central one. The measured overall efficiency
of the two lateral slitlets is ~85% of the direct transmission but drops to ~50% below 400 nm
due to reduced coating efficiency in the blue. An example of an IFU standard star is showed
in Figure 5.
Figure 4:
Top
: view of the effect of the IFU. The central field is directly transmitted to
form the central slitlet (green) while the each lateral field (in blue and red) are reflected
toward a pair of spherical mirrors and realigned at the end of the central slice to form
the exit slit.
Bottom:
The field before (left) and after the IFU (right). The IFU acts such
that the lateral fields seem to rotate around a corner of their small edge. The two white
slots are not real gaps but just guides to help visualize the top and the bottom of each
slice in the drawing.
