NICMOS provides imaging capabilities in broad, medium, and narrow band filters, broad-band imaging polarimetry, coronographic imaging, and slitless grism spectroscopy, in the wavelength range 0.8-2.5 µm. NICMOS is an axial instrument and has three adjacent but not contiguous cameras, designed to operate independently and simultaneously. Each camera has a different magnification scale, and is equipped with a dedicated 256 x 256 HgCdTe Rockwell array. The pixel size and field of view are 0".043 and 11"x11" in Camera 1 (referred to as NIC1), 0".075 and 19".2x19".2 in NIC2, and 0".2 and 51".2x51".2 in NIC3. Information about detector performance can be found in the NICMOS Instrument Handbook and at the NICMOS WWW page:
http://www.stsci.edu/ftp/instrument_news/NICMOS/Each camera is provided with its own set of filters, mounted on three independent wheels. There is a total of 20 filter positions on each wheel, of which one is BLANK and three of the others are occupied by either polarizers or grisms. The remaining 16 positions of each filter wheel are occupied by broad, medium, and narrow band filters. The list of these filters is given in the NICMOS Instrument Handbook. The filters (including polarizers and grisms) cannot be crossed with each other, and are used as single optical elements.
topnicmos.html
NIC1 and NIC2 each contain three polarizers, whose principal axes of transmission are separated by 120 degrees. The spectral coverage is fixed for each camera. The polarizers cover the wavelength range 0.8-1.3 µm in NIC1, and 1.9-2.1 µm in NIC2. Observations in the three polarizers of each camera are used to derive the Stokes parameters of linearly polarized light.
The filter wheel of NIC3 contains three grisms which can be used to perform slitless spectroscopy in the wavelength range 0.8-2.5 µm. The three grisms cover the range 0.8-1.2 µm, 1.1-1.9 µm, and 1.4-2.5 µm, respectively.
In NIC2, a coronographic spot is imaged onto the focal plane and provides a circular occulted region of 0".3 in radius (with a useful effective radius of 0".4). For coronographic imaging, an acquisition sequence is required at the beginning of the observation to center the target under the occulting spot.
Each 256 x 256 detector array is divided into four 128 x 128 quadrants, each of which is read out by an amplifier at the corner of the quadrant. There are four amplifiers in each camera. Unlike CCDs, infrared array pixels are read independently, implying that problems like charge transfer efficiency or bleeding are not present. The three cameras operate independently, implying that optical elements, integration times, and readout modes can be different in each.
stevens@stsci.edu Copyright © 1997, Association of Universities for Research in Astronomy. All rights reserved. Last updated: 11/13/97 16:58:34