Significant improvements in our understanding of various photometric effects have occurred in the more than nine years
of flight operations of the Infrared Array Camera aboard the Spitzer Space Telescope. With the accumulation of
calibration data, photometric variations that are intrinsic to the instrument can now be mapped with high fidelity. Using
all existing data on calibration stars, the array location-dependent photometric correction (the variation of flux with
position on the array) and the correction for intra-pixel sensitivity variation (pixel-phase) have been modeled
simultaneously. Examination of the warm mission data enabled the characterization of the underlying form of the pixelphase
variation in cryogenic data. In addition to the accumulation of calibration data, significant improvements in the
calibration of the truth spectra of the calibrators has taken place. Using the work of Engelke et al. (2006), the KIII
calibrators have no offset as compared to the AV calibrators, providing a second pillar of the calibration scheme. The
current cryogenic calibration is better than 3% in an absolute sense, with most of the uncertainty still in the knowledge of
the true flux densities of the primary calibrators. We present the final state of the cryogenic IRAC calibration and a
comparison of the IRAC calibration to an independent calibration methodology using the HST primary calibrators.
Electronic coupling effects such as Inter-Pixel Capacitance (IPC) affect the quantitative interpretation of image data
from CMOS, hybrid visible and infrared imagers alike. Existing methods of characterizing IPC do not provide a map of
the spatial variation of IPC over all pixels. We demonstrate a deterministic method that provides a direct quantitative
map of the crosstalk across an imager. The approach requires only the ability to reset single pixels to an arbitrary
voltage, different from the rest of the imager. No illumination source is required. Mapping IPC independently for each
pixel is also made practical by the greater S/N ratio achievable for an electrical stimulus than for an optical stimulus,
which is subject to both Poisson statistics and diffusion effects of photo-generated charge. The data we present illustrates
a more complex picture of IPC in Teledyne HgCdTe and HyViSi focal plane arrays than is presently understood,
including the presence of a newly discovered, long range IPC in the HyViSi FPA that extends tens of pixels in distance,
likely stemming from extended field effects in the fully depleted substrate. The sensitivity of the measurement approach
has been shown to be good enough to distinguish spatial structure in IPC of the order of 0.1%.
We compare a more complete characterization of the low temperature performance of a nominal 1.7um cut-off
wavelength 1kx1k InGaAs (lattice-matched to an InP substrate) photodiode array against similar, 2kx2k HgCdTe
imagers to assess the suitability of InGaAs FPA technology for scientific imaging applications. The data we present
indicate that the low temperature performance of existing InGaAs detector technology is well behaved and comparable
to those obtained for state-of-the-art HgCdTe imagers for many space astronomical applications. We also discuss key
differences observed between imagers in the two material systems.
Precision near infrared (NIR) measurements are essential for the next generation of ground and space based instruments. The SuperNova Acceleration Probe (SNAP) will measure thousands of type Ia supernovae up to a redshift of 1.7. The highest redshift supernovae provide the most leverage for determining cosmological parameters, in particular the dark energy equation of state and its possible time evolution. Accurate NIR observations are needed to utilize the full potential of the highest redshift supernovae. Technological improvements in NIR detector fabrication have lead to high quantum efficiency, low noise detectors using a HgCdTe diode with a band-gap that is tuned to cutoff at 1.7 μm. The effects of detector quantum efficiency, read noise, and dark current on lightcurve signal to noise, lightcurve parameter errors, and distance modulus fits are simulated in the SNAPsim framework. Results show that improving quantum efficiency leads to the largest gains in photometric accuracy for type Ia supernovae. High quantum efficiency in the NIR reduces statistical errors and helps control systematic uncertainties at the levels necessary to achieve the primary SNAP science goals.
We present the results of a detailed study of the noise performance of candidate NIR detectors for the proposed Super-Nova Acceleration Probe. Effects of Fowler sampling depth and frequency, temperature, exposure time, detector material, detector reverse-bias and multiplexer type are quantified. We discuss several tools for determining which sources of low frequency noise are primarily responsible for the sub-optimal noise improvement when multiple sampling, and the selection of optimum fowler sampling depth. The effectiveness of reference pixel subtraction to mitigate zero point drifts is demonstrated, and the circumstances under which reference pixel subtraction should or should not be applied are examined. Spatial and temporal noise measurements are compared, and a simple method for quantifying the effect of hot pixels and RTS noise on spatial noise is described.
We present the results of a study of the performance of InGaAs detectors conducted for the SuperNova Acceleration
Probe (SNAP) dark energy mission concept. Low temperature data from a nominal 1.7um cut-off wavelength 1kx1k
InGaAs photodiode array, hybridized to a Rockwell H1RG multiplexer suggest that InGaAs detector performance is
comparable to those of existing 1.7um cut-off HgCdTe arrays. Advances in 1.7um HgCdTe dark current and noise
initiated by the SNAP detector research and development program makes it the baseline detector technology for SNAP.
However, the results presented herein suggest that existing InGaAs technology is a suitable alternative for other future
Large format (1k × 1k and 2k × 2k) near infrared detectors manufactured by Rockwell Scientific Center and Raytheon Vision Systems are characterized as part of the near infrared R&D effort for SNAP (the Super-Nova/Acceleration Probe). These are hybridized HgCdTe focal plane arrays with a sharp high wavelength cut-off at 1.7 μm. This cut-off provides a sufficiently deep reach in redshift while it allows at the same time low dark current operation of the passively cooled detectors at 140 K. Here the baseline SNAP near infrared system is briefly described and the science driven requirements for the near infrared detectors are summarized. A few results obtained during the testing of engineering grade near infrared devices procured for the SNAP project are highlighted. In particular some recent measurements that target correlated noise between adjacent detector pixels due to capacitive coupling and the response uniformity within individual detector pixels are discussed.