and a 2 X 2 arcmin field of view.
NSO is developing a next-generation Near Infrared Magnetograph, NIM-2. NIM-2
is an imaging Stokes polarimeter that employs the Zeeman-sensitive Fe I
lines at 1564.9 and 1565.3 nm. Spectral selection is accomplished with a
rapidly tunable Fabry-Perot etalon from Queensgate Instruments (70 mm
diameter) in series with a tilt-tuned interference filter (1 nm FWHM).
Voltage-tuned liquid crystal retarders from Meadowlark Optics are used for
the polarization analysis. The initial detector is the 256 X 256 InSb array
used in the spectrograph-based NIM-1 (which will continue to be available).
The target detector is a 512 X 512 or larger InSb array from the Aladdin
collaboration in which NOAO is a partner. The NIM electronics have been
upgraded to provide frame rates up to 10 Hz. NIM-2 will take images in a 0.5
nm band around the iron lines with a spectral resolving power approaching
10 and a 2 X 2 arcmin field of view.
During two engineering runs in July and August, the NIM-2 components were assembled and tested. While a good bit of tuning will be needed to achieve optimum performance, the instrument has yielded the first magnetograms. Spectral resolution, currently about 0.02 nm, is expected to improve after fine adjustment of the optical system. An improved liquid crystal variable retarder (5 ms switching time) has recently been delivered. The new device should significantly improve polarization sensitivity over the first-generation instrument. We anticipate that NIM-2 will be commissioned and available to the scientific community in the first half of 1997.
Dave Jaksha, Christoph Keller, Doug Rabin