More Stray Light

I looked at files that were darks (detector blanked off) along with high and low flux images from  5 different filters (18a,  bp14100, N10692-9, Ocli O, BBP5030_5725).  I corrected for number of coadds and took the ITIME parameter as the integration time for each frame.  There were a couple filters where the data were taken with SUTR (4 frames).  I took the last frame except for one case where the signal was going non-linear, so I took the 2nd of the 4 frames.

Comparing the 4 frames in SUTRs, there is a clear difference between the "dark" regions when there is strong light and when there is not.  For the case where very little light is coming through, getting about 2 ADU/sec at 5 microns.  When there is a fair bit of light, the "dark" regions have more signal when the orders themselves have more signal.  Values are something like 5 ADU per second (peak is around 20 ADU per second)  This suggests there is light from echelon orders spilling into inter-order regions.  Consistent with echelle scattering 20% of the light at 5 microns.  


Looking at all frames, I also see clear correlation of "dark" region signal and peak signal.  For 18a, BP14100, N10692-2, and OCLI O, the extra light is at about the same level, ~10 ADU per second.  The amount of extra light at BBP5030 is more.   This suggests the echelle scattering is not as bad at long wavelengths.  


These results are not definitive, but they make some sense given what I expect for the grating performance (more scattered light as going to shorter wavelengths).

A better test for CD14 will be to include a dark when doing filter scans and to take the data with SUTR and shortening the exposure time as needed.