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GNIRS Detector Characteristics and Read Modes

PROPERTIES OF THE DETECTOR ARRAY

The properties of the Aladdin III detector array for the GNIRS science channel are given in the table below. The array has nicely uniform response, very low dark current and low read noise in the lowest background mode.  The bias voltage may be adjusted to modestly increase the well depth for thermal IR (L and M band) observations.  The four read modes which can be used for GNIRS observations, and the read noise and exposure times for each are described in the second table.

Detector Characteristics
Array Aladdin III InSb (Hughes SBRC)
Pixel format 1024x1024 27-micron pixels
Spectral Response 0.9 to 5.5 microns
Dark Current 0.15 e-/s/pix
Gain 13 e-/ADU
Well depth (near-IR) 90,000 e-
Well depth (thermal-IR) 180,000 e-
Quantum efficiency about 90%
Flat field repeatability TBD
Residual image retention Yes

Read Modes and Associated Overheads

The detector read noise can tradeoff with the amount of time required to read out the array. The best choice depends on the brightness of the object and the background at a given wavelength (see Observing Strategies page for more guidance).

Read Modes
Read Mode
 Low Noise
Reads 		Digital
Averages 		Bias Level
(mV) 		Read Noise
(e-) 		Saturation
(e-) 		Overhead/Read
minimum exp. time* (sec) 		Recommended
min. exp time* (sec) 		Recommended
Use
High Background (Thermal) or Very Bright Objects 1
 1
 600
 145
 180,000
 0.2
 <1.0
 L & M
Obs.
Medium Background/
Bright Objects 		1
 16
 300
 38
 90,000
 0.6
 ~2.0
 Max. Exp.
~20s
Low Background/
Faint Objects 		16
 16
 300
 12
 90,000
 9.0
 18.0
 Exp.
~20 - 60 sec
Very Low Background/
Very Faint Objects 		32
 16
 300
 7
 90,000
 18.0
 60.0
 Exp.
>60 sec

* The minimum exposure times, which are not recommended, are the times required to read the array. The recommended minimum exposure times allow efficient observing (spending at least 90% of the exposure time actually exposing the array as opposed to reading it). 

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Last update Dec. 16, 2004; Bernadette Rodgers and Greg Doppmann