NIRS : Near-Infrared Spectrometer

What's the NIRS !?

The Near-Infrared Spectrometer (NIRS: Noda et al. 1994, Noda et al. 1996; see IRSA IRTS Bibliography Listing) is a grating spectrometer with two 12 element InSb linear arrays, and is one of the four focal-plane instrumens of the Infrared Telescope in Space (IRTS) mission, which was launched in March 1995. The NIRS was designed to measure the absolute sky brightness with coarse spectral resolution ; searching for extragalactic background light is the primary purpose of the obsevations. The wavelength coverage of the NIRS ranges from 1.4 to 4.0 micron with a spectral resolution of 0.12 micron. The field of view is 8' x 8'. The NIRS has been calibrated and tested with the flight IRTS telescope in the laboratory. The response and noise were found to be as expected from the design values. After integrating all of the focal-plane instruments with the telescope into the flight cryostat, NIRS shows good performance and is able to achieve a high sensitivity in orbit.


Size 135 x 154 x 102 mm3 (over all)
Weight 1.18 kg
Entrance apaerture 1.4 x 1.4 mm2
Field of view 8 x 8 arcmin2
Temperature 1.8 K
Detection system
Detector InSb
Element size 1 x 0.5 mm2 (per element)
Number of elements 24 (2 x 12 elements)
Wavelength coverage 1.43-2.54 micron, 2.88-3.98 micron
Resolution 0.12 (0.10 at channel 1)
Total capacitance ~50 pF
Readout method Charge-integrated amplifier
Temperature of J-FETs ~70 K

Observation Targets

  • Zodiacal light / Interplanetary dust
  • Galactic diffuse light / UIR band at 3.3 microns
  • Late-type stars
  • Extragalactic background light

Photographs of the NIRS
        NIRS assembled                                 NIRS detector & J-FET

More photographs of NIRS are available here.