Spectrographs: Integral Field Units
E
N C Y C L O P E D I A O F
A
S T R O N O M Y A N D
A
S T R O P H Y S I C S
Figure 2.
Schematic of IFU types (from Content 1997).
Figure 3.
OASIS optical layout.
Slicer IFU
The slicer IFUs use mirrors in the telescope focal plane
to cut the field of view into a number of strips which are
then rearranged into a one-dimensional long strip. The
slicer is composed of two sets of mirrors: the first set slices
the field of view in a number of strips and reflects them
into different directions while the second set rearranges
the strips and aligns them into one continuous long strip.
Slicer IFUs are comparable with fiber IFUs in terms of
spectral coverage, but they are more efficient in terms of
packing efficiency as the spatial sampling is continuous
along each strip. The tilt of each submirror produces a
defocus between the two edges of each slice. This defocus
translates into losses in spatial resolution and throughput.
This gives a practical limit to the maximum number of
slices that can be accommodated by such an IFU as defocus
increases with the number of slices.
The only working slicer IFU in operation today is the
three-dimensional instrument built at MPE (Weitzel et al
1996). It operates in the near infrared (H and K band)
and has been successfully used on a number of 4 m class
telescopes.
A variation of this principle which limits the defocus
has been proposed by Content (1997) (figure 4): the mirrors
have curved surfaces to allow the pupil-relay mirrors to be
reduced in size. The tilt of each component is then reduced
and consequently the defocus aberrations are decreased.
Applications
IFUs have been successfully used on a large variety of
objects, from the study of
PLANETARY SURFACES
to the most
distant
QUASARS
.
A good example of IFU possibilities is given in the
study of the Einstein cross, the gravitationally lensed
Copyright © Nature Publishing Group 2001
Brunel Road, Houndmills, Basingstoke, Hampshire, RG21 6XS, UK Registered No. 785998
and Institute of Physics Publishing 2001
Dirac House, Temple Back, Bristol, BS1 6BE, UK
3
