THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1995 AND 1996

5. Instrumentation Development

5.2. MICHELLE

The powerful 7 - 25 micron imager/spectrometer MICHELLE, the final optical design for which was illustrated in the last Report, is at the peak of its development activity. Delivery to UKIRT is expected in 1999. The instrument is equipped with two 24-place filter wheels, currently expected to be populated with blocking and line-selection filters, calibration etalons and a polariser. The 5-position grating drum provides for spectral resolving powers of R=250, 1000 and 3000 in the 10 micron (N) band, and R=200 and 1000 across the 20 micron (Q) band. An echelle covers both bands at resolving powers ranging from 15,000 to 30,000. Most of the development hurdles associated with this ambitious instrument have been surmounted. The grating-exchange mechanism has been demonstrated to be effective and reliable, and the Joule-Thompson three-stage cooler has been run for several weeks at liquid helium temperatures. Currently the opto-mechanical sub-systems are being aligned ready for their incorporation into the complete vacuum vessel. The first cooldown is scheduled for spring 1998.

MICHELLE is intended to be delivered with a Santa Barbara Research Corporation 240320 pixel Si:As IBC detector, which has 75 micron square pixels. This will give the spectrometer a pixel FOV of 0.38 arcseconds and the imager 0.21 arcseconds (note that the FWHM of the Airy pattern of UKIRT at 10 microns is 0.55 arcseconds). MICHELLE will be shared between UKIRT and GEMINI-North, on which it is intended to be the first mid-infrared instrument. The fore-optics are therefore interchangeable (upon warmup) between f/16 and f/36.