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Determination of the gain
Code
Using it
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Determination of the gain
The determination of the EM gain of the CCD is best done by fitting the
histogram of many low-light frames. Typically, the dark+CIC noise of a
30ms frame itself is a sufficient amount of signal to determine
accurately the EM gain with about 200 512x512 frames. The following
function, emGain, takes as an input a cube of frames and fit the
histogram of all the pixels with the EM stage output probability
function. The function returns the EM gain of the frames as well as the
read-out noise and the mean signal level of the frames.
For more informations regarding my recent work involving emccds, please
visit www.nuvucameras.com.
The code
The IDL code can be downloaded here.
Using it
The code can be simply used with a script like this one:
dark = file_search('*.fits') ; Load the dark frames filenames
adu_per_electron = 0.1 ; To convert ADU in electrons
im = readfits(dark[0], /silent)
sz = size(im)
dark_frames = fltarr(n_elements(dark), sz[1], sz[2])
for i=0, n_elements(dark)-1 do dark_frames[i,*,*] = readfits(dark[i], /silent)
gain = emGain(dark_frames, bias, ro, counts)
ro /= adu_per_electron
gain /= adu_per_electron
print, 'Readout noise is ' + strtrim(ro,2) + ' electrons'
print, 'EM gain is ' + strtrim(gain,2) + ' electrons/electron'
print, 'Mean signal level is ' + strtrim(counts,2) + ' electron/pixel'
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