Integral Field Spectrograph Optical Design


As shown in the previous section, the image formed by the diffraction-limited coronagraph suffers from wavelength dependent speckles. The aim of the Integral Field Spectrograph (IFS) is to take the image plane of the coronograph, and form a spectrum for every pixel in this image plane. The coronagraph image plane is divided up using a grid of lenslets, which act as spatial filters forming a grid of pupil images.

For each lenslet, the beam diverges after these pupil images, where it is then collimated, then dispersed by passing through a prism, then refocussed onto the detector.

The optical design for the IFS was developed by Dave King. It consists of:

  • A lenslet array
  • A dioptric collimator of 160mm focal length, consisting of 5 lenses of different glasses, with only spherical surfaces
  • A prism/disperser element
  • A catadioptric camera of 400mm focal length, consisting of a meniscus corrector lens, a spherical mirror, and a field-flattening lens in front of the detector.
  • Two fold mirrors were included to help with packaging.

    The optical design was modelled using the Zemax optical design software. The complete optical train will be built into a cryogenic enclosure, cooled to 78K (-195 degrees Centigrade). The effects of the thermal contraction are taken into account in the optical design.

    A powerpoint presentation of the optical design is available here


    Created by David King on 29 January, 2007