Linearity sequences

LINEARITY and SATURATION

Two pretty good linearity sequences were taken on 20090608, both done with NB118. The first sequence was done as recommended with light levels ~1200-1300 ADU/sec/pixel, sampling at 2s exposure time intervals all the way up to saturation and then back down again. These exposures were interleaved with exposures at constant exposure time of 7.5s (~10K ADU) to monitor the stability of the light source. The second sequence was done with 0.5s intervals and with a much lower light level (~150 ADU/sec/pixel). This was done to look for any non-linear behaviour at low flux.   Analysis of the sequences gives the following results:

-- there is a small non-linearity that affects all detectors at flux level <~1000 at about the 1-2% level.  This is totally invisible to the normal linearity analysis as it is below the minimum flux when a 'normal' linearity sequence is taken

-- the saturation level varies measurably from detector to detector. It is also quite clear that parts of each detector saturate at different levels. This is particularly noticeable in detector #5. However, once a good saturation level was established, all the detector curves are well fit by a 4th order polynomial.

-- The dome lights were much more stable this time with a maximum variation of generally < 1%

The following table summarises the derived results for saturation and percentage non-linearity at 10000 ADU

detector     saturation(ADU)    non-linearity (%)
------------      ------------------------    --------------------------
    1                 33000                      2.2
    2                 32000                      3.3
    3                 33000                      3.8
    4                 32000                      3.5
    5                 24000                      2.0
    6                 26000                      3.0
    7                 35000                      2.0
    8                 33000                      3.4
    9                 35000                      3.3
   10                35000                      4.4
   11                37000                      4.6
   12                34000                      2.6
   13                33000                     10.0
   14                35000                      2.7
   15                34000                      1.7
   16                34000                      3.3