The attributes of the scientific-grade 4k linear CID51 sensor are presented. The CID51 sensor is fabricated
using 0.18 μm technology. The 0.18 μm design rules permit proximity-coupling of the two photogates within the pixel
required for non-destructive readout of the charge. The 14 μm by 50 μm pixels are arranged on two evenly staggered
2080-pixel rows. The result is a randomly addressable 4160 pixel array with an effective pitch of 7 microns and an
effective height of 100 microns. The sensor incorporates parallel pixel processing with on-chip correlated double
sampling. The critical unique feature of the CID51 is the 32 analog row storage registers (RSR) per pixel. These RSRs
allow for the time resolved sampling of the 4160 pixel spectrum and can be randomly read out at rates as high as 8 MHz.
The signal storage of up to 32 samples per pixel is non-destructive allowing for the integration of spectroscopic events
with unprecedented microsecond time resolution. Alternatively, because pixels can be randomly accessed for readout or
reset, intensely illuminated pixels can be quantitatively sampled and rapidly cleared of photon-generated charge, while
weakly illuminated pixels are simultaneously allowed to integrate. Thus, the effective integration time can be varied
from pixel to pixel based upon the observed photon flux vastly expanding dynamic range. Full spectrum acquisition
provides all of the spectral content, including background continuum information for accurate photometry and spectrum
to spectrum calibration. The CID51 device is suited for scientific applications demanding high dynamic range and/or
time resolved capabilities.
We report on new development and testing of FORCAST, the Faint Object infraRed Camera for the SOFIA Telescope. FORCAST will offer dual channel imaging in discrete filters at 5 - 25 microns and 30 - 40 microns, with diffraction-limited imaging at wavelengths > 15 microns. FORCAST will have a plate scale of 0.75 arcsec per pixel, giving it a 3.2 arcmin x 3.2 arcmin FOV on SOFIA. In addition, a set of grisms will enable FORCAST to perform long slit and cross-dispersed spectroscopic observations at low to moderate resolution (R ~ 140 - 1200) in the bandpasses 4.9 - 8.1 microns, 8.0 - 13.3 microns, 17.1 - 28.1 microns, and 28.6 - 37.4 microns. FORCAST has seen first light at the Palomar 200 inch telescope. It will be available for astronomical observations and facility testing at SOFIA first flight.
We have developed a high speed, flexible, data acquisition system and targeted it to astronomical imaging. The system is based on Field Programmable Gate Arrays (FPGAs) and provides a gigabit/sec fiber optic link between the electronics located on the instrument and the host computer. The FPGAs are reconfigurable over the fiber optic link for maximum flexibility. The system has initially been targeted at DRS Technologies' 256x256 Si:As and Si:Sb detectors used in FORCAST1, a mid-IR camera/spectrograph built by Cornell University for SOFIA. The initial configuration provides sixteen parallel channels of six Msamples/second 14-bit analog to digital converters. The system can coadd 256x256 images at over 1000 frames per second in up to 64 different memory positions. Array clocking and sampling is generated from uploaded clocking patterns in two independent memories. This configuration allows the user to quickly
create, on the fly, any form of array clocking and sampling (destructive, non-destructive, sample up the ramp, additional reset frames, Fowler, single frames, co-added frames, multi-position chop, throw away frames, etc.) The electronics were designed in a modular fashion so that any number of analog channels from arrays or mosaics of arrays can be accommodated by using the appropriate number of FPGA boards and preamps. The preamp/analog to digital converter boards can be replaced as needed to operate any focal plane array or other sensor. The system also provides analog drive capability for controlling an X-Y chopping secondary mirror, nominal two position chopping, and can also synchronize to an externally driven chop source. Multiple array controllers can be synchronized together, allowing multi-channel systems to share a single chopping secondary, yet clock the focal planes differently from each other. Due to the flexibility of the FPGAs, it is possible to develop highly customized operating modes to maximize system performance or to enable novel observations and applications.
The Infrared Spectrograph (IRS) is one of three science instruments on the Spitzer Space Telescope. The IRS comprises four separate spectrograph modules covering the wavelength range from 5.3 to 38 μm with spectral resolutions, R~90 and 650, and it was optimized to take full advantage of the very low background in the space environment. The IRS is performing at or better than the pre-launch predictions. An autonomous target acquisition capability enables the IRS to locate the mid-infrared centroid of a source, providing the information so that the spacecraft can accurately offset that centroid to a selected slit. This feature is particularly useful when taking spectra of sources with poorly known coordinates. An automated data reduction pipeline has been developed at the Spitzer Science Center.
We report laboratory tests amd development progress for the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST). FORCAST is a two-channel camera with selectable filters for continuum and line imaging in the 5 - 40 micron wavelength region. Simultaneous imaging will be possible in the two channels: 5 - 25 microns using a Si:As 256x256 blocked impurity band (BIB) detector array, and 25-40 microns using a Si:Sb BIB. FORCAST will sample 0.75 arcseconds per pixel allowing a 3.2'x3.2' instantaneous field-of view in both channels simultaneously. Imaging will be diffracted limited for lambda> 15 microns on the SOFIA telescope. Since FORCAST operates in the wavelength range where the seeing is best from SOFIA, it will provide the highest spatial resolution possible from the airborne observatory. In addition to imaging, the FORCAST optical design provides for a simple upgrade to include spectroscopic observations using grisms mounted in the filter wheels. FORCAST will be available for facility testing and astronomical observations at SOFIA first (f)light.
This paper presents results on performance testing of mid-infrared detector arrays for the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST). FORCAST is a two-channel camera that utilizes a Si:As blocked impurity band (BIB) 256 x 256 detector array for imaging through discrete filters at 5 - 25 microns, and a Si:Sb BIB 256 x 256 detector array for imaging at 25 - 40 microns, over a 3.2' x 3.2' field of view, under high thermal background conditions. DRS Technologies has designed and fabricated several Si:As BIB and Si:Sb BIB engineering grade detector arrays which we test as candidate arrays for FORCAST. We present their initial laboratory test performance results.
The availability of both large aperture telescopes and large
format near-infrared (NIR) detectors are making wide-field NIR
imaging a reality. We describe the Wide-field Infrared Camera
(WIRC), a newly commissioned instrument that provides the Palomar
200-inch telescope with such an imaging capability. WIRC features
a field-of-view (FOV) of 4.33 arcminutes on a side with its
currently installed 1024-square Rockwell Hawaii-I NIR detector. A
2048-square Rockwell Hawaii-II NIR detector will be installed and
commissioned later this year, in collaboration with Caltech, to
give WIRC an 8.7 arcminute FOV on a side. WIRC mounts at the
telescope's f/3.3 prime focus. The instrument's seeing-limited
optical design, optimized for the JHK atmospheric bands,
includes a 4-element refractive collimator, two 7-position filter
wheels that straddle a Lyot stop, and a 5-element refractive f/3
camera. Typical seeing-limited point spread functions are slightly
oversampled with a 0.25 arcsec per pixel plate scale at the detector. The entire optical train is contained within a cryogenic dewar with a 2.5 day hold-time. Entrance hatches at the top of the dewar allow access to the detector without disruption of the optics and optical alignment. The optical, mechanical, cryogenic, and electronic design of the instrument are described, a commissioning science image and performance analyses are presented.
We report final design details and development progress for the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST). FORCAST is a two-channel camera with selectable filters for continuum and line imaging in the 5-40 micron wavelength region. Simultaneous imaging will be possible in the two-channels--5-25 microns using a Si:As 256×256 blocked impurity band (BIB) detector array, and 25-40 microns using a Si:Sb BIB. FORCAST will sample 0.75 arcseconds per pixel allowing a 3.2'×3.2' instantaneous field-of-view in both channels simultaneously. Imaging will be diffraction limited for lambda > 15 microns. Since FORCAST operates in the wavelength range where the seeing is best from SOFIA, it will provide the highest spatial resolution possible from the airborne observatory. In addition to imaging, the FORCAST optical design provides for a simple upgrade to include spectroscopic observations using grisms mounted in the filter wheels. We report improvements to the optical system and progress in construction of this SOFIA facility instrument and its subsystems. FORCAST will be available for facility testing and astronomical observations at SOFIA first (f)light.
We are constructing a facility-class, mid/far-infrared camera for the Stratospheric Observatory for Infrared Astronomy (SOFIA). The Faint Object infraRed CAmera for the Sofia Telescope (FORCAST) is a two-channel camera with selectable filters for continuum imaging in the 5 - 8, 17 - 25 micron, and/or 25 - 40 micron regions. The design supports simultaneous imaging in the two-channels. Using the latest 256 X 256 Si:As and Si:Sb blocked-impurity-band detector array technology to provide high-sensitivity wide- field imaging. FORCAST will sample images at 0.75 arcsec/pixel and have a 3.2' X 3.2' instantaneous field- of-view. Imaging is diffraction limited for lambda > 15 microns.
SCORE is a cross-dispersed echelle spectrograph, built as a prototype for the Short-High module of SIRTF's IRS instrument. It operates over the 7.5-15 micrometers N-band atmospheric window, and has ben used on Palomar's Hale telescope several times since November, 1996. Since the initial run, a number of improvements have ben undertaken or are in the process being undertaken which enhance SCORE's performance and simplify its operation. One such addition, now completed, is a second detector array which serves as a slit-viewer with 12 inch diameter field of view around the slit. This viewer allows easy acquisition and guidance for sources with dim or absent optical counterparts, and accurately registers the position of the slit on the source with the recorded spectrum. Software written in the IDL environment optimizes the extraction of spectra form SCORE's mid-IR crossed-echelle data. The echelle, while providing the advantage of increased pixel utilization, introduces several difficulties, including curved orders, order cross- talk, and differentially slanted lines. These and other instrumental artifacts must be removed to achieve the highest spectral signal-to-noise. The pixel efficiency will be further increased by the use of a grism predisperser. The grism will provide approximately even spacing between orders of the echelle, in contrast with the decreasing spacing towards shorter wavelength orders generated by the current grating. SCORE is already one of the most powerful short- slit spectrographs operating in this wavelength band, and, with the implementation of these improvements, will deliver even greater capability.
We describe Corneirs NIR camera system for the Hale 200” telescope adaptive optics system at Palomar Observatory. The instrument is under construction at this time, and we expect first light at the telescope in December 1997. Here we summarize the camera’s design as well as its expected performance.
Cryogenic telescopes in space offer dramatic reduction in thermal IR background flux. Outstanding performance in the areas of detector dark current, read noise, and radiation hardness are required to take full advantage of the sensitivity improvements possible with such facilities, especially in very low flux (2 to 100 photons/pixel/sec) applications such as the Infrared Spectrograph on SIRTF. We present our testing methods and our results on Si:As and Si:Sb block impurity band (BIB) detectors produced by Rockwell International for our SIRTF and WIRE applications. Remarkable recent results are the reduction of the multiple-sampling read noise to 30 electrons, reduction of dark current to 10 e-/s for Si:As and 40 e-/s for Si:Sb, the use of an antireflective coating to improve the detective quantum efficiency for Si:As, extension of the useful wavelength range of Si:Sb to 40 microns, and confirmation that lab data on a 50 s time scale can be extrapolated to integration times at least 10 times longer.