SPIRE Spectrometer

1
The Spectrometer for SPRE

• Bruce Swinyard
• Rutherford Appleton Laboratory
• U.K.

2
Co-conspirators
Kjetil Dohlen Didier Ferrand Jean-Paul Baluteau
Dominique Pouliquen Pascal Dargent Laboratoire
dAstrophysique de Marseille Guy Michel -
Meudon Jerome Martignac CEA-SAp Peter Ade
Peter Hargrave Matthew Griffin Cardiff
University Donald Jennings - GSFC Martin Caldwell
- RAL
3
History

• The Phase A bolometer instrument proposed for
  FIRST was a tandem FP abandoned because of
  complexity of design
• Design study for SPIRE was based on a grating
  spectrometer
• Concluded that the space available in the
  instrument was not enough to get Rgtfew hundred
• FTS was studied originally a Martin-Puplett
  polarising FTS -gt 50 throughput loss
• Peter Ade at Cardiff produced broad band
  intensity beam splitters in the 15-50 cm-1 range
• A twin beam splitter Mach-Zehnder type FTS is
  therefore possible
• In principle 100 throughput can be achieved
• In practice there is 50 channel loss because the
  detectors cannot cover 15-50 cm-1
• System is background limited therefore a loss of
  raw sensitivity for known line on single point on
  sky is factor 5-10 compared to a grating with
  100 mK detectors and 2-5 for 300 mK detectors
• 100 mK temperatures not a reasonable option for
  SPIRE

4
An Aside What SPIRE could have been (and was
in 1997)
5
Design Overview
6
Optical Design (i)
7
Optical Design (ii)
Lens added to focal plane to make beam telecentric
8
Mapping
CO line emission region
Dusty cold region
9
Beam Splitters

• Based on Cardiff University FIR/sub-mm filter
  technology
• Very flat response with 2RTR2 T2 to good
  accuracy

10
Mechanism (i)

• Based on design by GSFC
• Prototypes built by GSFC and provided to LAM for
  evaluation
• Position encoder is a modified Heidenhain LIP401a
  optical encoder
• Additional/backup position information provided
  by Schaevitz MHR100 LVDTs over a limited movement
  range
• Actuator is designed in-house at LAM based on
  Kimco device

11
Mechanism (ii)
12
Optical Encoder
13
Prototype Tests (ii)
14
Spectral Performance
15
Summary

• The SPIRE imaging FTS has guaranteed resolution
  of 0.4 cm-1 over a 2.6 arcmin FOV
• Resolution 0.04 cm-1 (R1000 at 250 micron) for
  on-axis positions and over some portion of FOV
• Narrow band photometry (2 cm-1) with same
  instrument over 2.6 arcmin FOV
• Sensitivity 2-3e-17 W m-2 for 80 K telescope
  with 4-K telescope a factor of 50-100 better with
  same detectors
• Step and look mode can be employed for best
  continuum performance

16
European SPICA Study

• After discussion with Prof. Matsumoto in June 04
  we have kicked off a small (i.e. unfunded!) study
  into the possibility of Europe providing an
  instrument for SPICA
• Institutes so far expressing an interest are in
  U.K. (RAL, Cardiff, IC, Kent U and Sussex U)
  Netherlands (SRON) and Germany (MPE)
• Keeping study team small at present in order to
  better define what type of instrument we are
  interested in/fits with European interests and
  best exploits SPICA capabilities
• Initial thoughts are that a spectrometer covering
  27 to 160 ?m (H2 to CII) will provide continuity
  with European interests in ISO Herschel and JWST
• This wavelength range also best exploits the low
  background offered by SPICA and gives most bang
  for euro in science
• What type of spectrometer (resolving power
  precise wavelength range imaging etc) will be
  our next point of discussion!