SPIFI was the first submillimeter direct detection imaging spectrometer.  It was designed for use in the far-IR and submm (200, 350, 450 micron) windows available to the 1.7 m Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at the South Pole, and in the submm (350 and 450 micron) windows available to the James Clerk Maxwell Telescope (JCMT) on Mauna Kea in Hawaii. SPIFI's detector is a 5 x 5 element array of monolithic silicon bolometers cooled to 60 mK in an adiabatic demagnetization refrigerator. SPIFI uses free standing metal mesh Fabry-Perot interferometers to deliver spectroscopic images at resolving powers as large as R = 10,000 (or a velocity resolution, as small Dv = 30 km/s) over the entire array.


Nearly all submillimeter spectroscopy to date has been done with heterodyne receivers.  These receivers will remain the spectrometers of choice for very high velocity resolutions: ∆v < 5 --> 10 km s-1. However, recent advances in bolometer technology permit background limited direct detection to similar resolutions.  It can be shown that direct detection is in principle more sensitive than phase sensitive schemes (cf. Harris, A. I. 1990, in "From Ground-Based to Space=Bourne Sub-mm Astronomy", ESA SP-314, 165).

Monochrometers such as grating spectrometers and Fabry-Perot interferometers (FPIs) are the instrument of choice for background limited systems.  However, for spectral resolutions > 10,000 at 370 µm, a single pass grating needs to be > 1.8 m long!  Clearly a multiple pass instrument such as FPI is preferred.

In addition, the South Pole has the lowest water vapor burden of any developed site on the planet.  During the winter, the 350 and 450 µm windows are always open.  This results in a transparency that can be twice that of Mauna Kea.  The 200
µm window is also open in mid-winter.  Until the Stratospheric Observatory for Infrared Astronomy (SOFIA), SPIFI on AST/RO was the only system viable for large scale, sensitive [N II] work. The observation of the [N II] line in the Carina nebula was part of the PhD thesis of Tom Oberst.

The Antarctic Submillimeter Telescope and Remote Observatory located at the South Pole.

The James Clerk Maxwell Telescope located close to the summit of Mauna Kea, Hawaii.

Highlights of SPIFI at JCMT

38 µm continuum image (Latvakoski et al. 1999)

SPIFI Image Gallery

For more information about the James Clerk Maxwell Telescope, visit the JCMT Homepage.
For more information about the
Antarctic Submillimeter Telescope and Remote Observatory
AST/RO Homepage.