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Near Infrared Magnetograph: The Sequel (1Dec94)
(from NSO, NOAO Newsletter No. 40, 1 December 1994)

NIM-2 is a concept for a near-infrared imaging magnetograph based on a
narrowband filter and an infrared array camera. It will complement rather
than replace the existing spectrograph-based NIM instrument. A principal
objective of NIM-2 is to study the evolution of the vector magnetic field in
active regions. NIM-2 will use the 1.56 um g = 3 line of Fe I to provide
true field strengths in sunspots and plages. This line is completely split in
kilogauss fields, so the three polarized Stokes components are comparable in
magnitude--an advantage for vector magnetometry. At the expense of
somewhat lower spectral resolution, NIM-2 will have an advantage over
NIM in studying spatial structure and evolution because the whole spatial
field will be imaged simultaneously rather than built up by scanning.

NIM-2 will use the same infrared array camera (Amber 256 X 256) and data
acquisition system as NIM. A Queensgate Fabry-Perot etalon was ordered at
the end of the last quarter. The etalon will be stable to 0.02 cm^-1 and
tunable over a free spectral range of 3 cm^-1 at video rates. Rapid sampling
of the line profile and nearby continuum will be synchronized with
polarization modulation by liquid crystal variable retarders.

Doug Rabin

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