NICMOS Instrument Handbook for Cycle 11

Chapter 7: 
NICMOS Detectors

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In this chapter . . .

Detector basics Detector Characteristics Detector Artifacts

 

In this chapter, we first briefly explain the physical principles of the NICMOS detectors. We then report on a number of properties that have significance for the scientific performance of NICMOS. Many of these properties are temperature dependent, which is important since the operating temperature for NICMOS under NCS is not yet well known. Expectations for performance in Cycle11 come from a set of monitoring programs executed at the end of Cycle 7N, during the period November 1998 - January 1999. These programs monitored darks, flat-field and focus position while NICMOS was warming up, due to cryogen exhaustion. During warm-up, the NICMOS temperature increased from ~ 62 K to environment temperature, crossing the region around 72 - 77 K, which is the target temperature range under NCS operations. We will discuss how the various aspects like e.g. quantum efficiency, read-noise, and dark current depend on temperature, and how this will affect the NICMOS sensitivity. Also, we discuss a number of detector artifacts like shading, amplifier glow, and others, all of which can be corrected, either in pipeline processing or at the analysis level.

We emphasize again that the expected operating temperature of the NICMOS detectors is still rather uncertain, somewhere between 75 and 86 K, with a current best estimate of 78.5 K. The expected NICMOS performance, however, does not drastically change over this temperature range.