The basic properties of the Aladdin detector array for the NIRI science channel are given in the table below. The array has nicely uniform response and very low dark current. Various size centered subarrays may be read out instead of the full 1024x1024 array. The bias voltage may be adjusted to modestly increase the well depth for thermal IR (L and M band) observations.

The linearity of the array is better than 1% until the flux level reaches approximately 70% of the full well, or 11,000 ADU in a frame with 1 coadd and 1 read pair. Most observations are kept well below this level for both standard stars and science observations. Standard star flux levels are typically at the same level as the background in the science frames.

The saturation level in a single coadd and low-noise read pair is about 16,000 ADU (although well depth varies with quadrant and region). Because of the way the array is operated (reset-read-read), progressively brighter sources will approach saturation and then begin to get FAINTER as the array begins to saturate in the time between the reset and the first read. Saturated stars often show a central hole, sometimes even becoming negative in the core. Because the array reads from the corners to the center, along rows, this effect may be different at different places in the array. In particular, when the whole array is saturated, values in the center will pass the saturation value and start approaching zero again. A gradient in the background with saturation near the edges and lower levels in the middle indicates a highly saturated array!

Image persistence is small in this array, but saturated or nearly saturated images will leave a ghost in one or two subsequent frames. The persistence of a very bright source is typically 0.5 to 1% in the next frame and less than 0.1% by the third frame.

Three read modes have been defined to optimize use of the array. For high background environments (e.g., in the thermal IR), the array is read once at the beginning and once at the end of the exposure and the difference is recorded. In medium background situations (e.g., f/6 broad band JHK imaging) the same basic mode is used, but the beginning and end reads are digitally averaged 16 times. In low-background observations (e.g., f/32 observations, 1-2.5um narrow band imaging and 1-2.5um faint object spectroscopy), the array is read 16 times at the beginning and the end of the exposure, with the above digital averaging also taking place during each read. The read noise associated with these three modes is shown below.