An echelle spectrograph has been constructed for astronomical use at mid-infrared wavelengths. It contains a liquid-helium-cooled echelle grating and a 10 X 64 pixel Si:As impurity band detector array. The array is used to measure a 64-point spectrum with 1000-25,000 resolving power at each of ten points spaced by 0'.'4-3" along a slit. The spectrograph can be used at wavelengths between about 4 and 25 |xm. The instrument has proven to be photon-noise limited with an overall quantum efficiency ranging from ~ 0.02 at 4 jxm wavelength to 0.2 near 20 pan.
An IR camera has been built at the University of California at Berkeley for astronomical observations. The camera has been used primarily for high angular resolution imaging at mid-IR wavelengths. It has been tested at the University of Arizona 61- and 90-in. telescopes near Tucson and the NASA Infrared Telescope Facility on Mauna Kea, HI. In the observations the system has been used as an imager with interference coated and Fabry-Perot filters. These measurements have demonstrated a sensitivity consistent with photon shot noise, showing that the system is limited by the radiation from the telescope and atmosphere. Measurements of read noise, crosstalk, and hysteresis have been made in our laboratory.
The Multiband Imaging Photometer for SIRTF (MIPS) is to he designed to reach as closely as possible the fundamental sensitivity and angular resolution limits for SIRTE over the 3 to 700pm spectral region. It will use high performance photoconductive detectors from 3 to 200äm with integrating JFET amplifiers. From 200 to 700pm, the MIPS will use a bolometer cooled by an adiabatic demagnetization refrigerator. Over much of its operating range, the MIPS will make possible observations at and beyond the conventional Rayleigh diffraction limit of angular resolution.
The Multiband Imaging Photometer for Spitzer (MIPS) provides long wavelength capability for the mission, in imaging bands at 24, 70, and 160µm and measurements of spectral energy distributions between 52 and 100µm at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The Si:As BIB 24µm array has excellent photometric properties, and measurements with rms relative errors of 1% or better can be obtained. The two longer wavelength arrays use Ge:Ga detectors with poor photometric stability. However, the use of 1.) a scan mirror to modulate the signals rapidly on these arrays, 2.) a system of on-board stimulators used for a relative calibration approximately every two minutes, and 3.) specialized reduction software result in good photometry with these arrays also, with rms relative errors of less than 10%.
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